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TxDOT GPS User`s Manual - e

1. Caution Readers who rely on any printed portions of the manual should check the online manual regularly for revisions GPS User s Manual 1 6 TxDOT 8 2005 Chapter 2 Background Contents Section Overview unudaadiunied nue ede ea ede eee 2 2 Section 2 Surveying With GPS tr adan 2 3 Section 3 Surveying Vertical Networks with GPS oooonocccnnococcoocccnoncnononccononcconanccnnnncnnnnos 2 5 PC CLL 4 Coordinate Systems ere wai evince cua E a a a co an ie ecaahe 2 7 GPS User s Manual 2 1 TxDOT 8 2005 Chapter 2 Background Section 1 Overview Section 1 Overview Purpose The purpose of this chapter is to provide the user with general information regarding the use of GPS for design grade surveying Outlined survey processes provide an understanding of relationships and their components GPS User s Manual 2 2 TxDOT 8 2005 Chapter 2 Background Section 2 Surveying with GPS Section 2 Surveying with GPS Survey Background Information All GPS surveying techniques are based upon interferometric observations of radio signals from a network of orbiting satellites These signals are processed to compute station positions by trilateration the positions of the satellites and computed ranges are used to determine the antenna position These positions are computed in an Earth centered Earth Fixed ECEF Cartesian coordinate x y Z system which can be converted to geodetic curvilinear coordinates l
2. State Plane Coordinates State plane coordinates are special definitions of Transverse Mercator and Lambert conformal mapping projections adopted by statute in the USA There is one set of such zones for NAD 27 and another for NAD 83 static surveying Static is a method of GPS surveying using long occupations hours in some cases to collect GPS raw data then postprocessing to achieve sub centimeter precisions GPS User s Manual B 25 TxDOT 8 2005 Appendix B Glossary static network A static network is a network that describes the geometry and order in which GPS baselines collected using static and fast static techniques are organized and processed The baseline processor first examines the project for points with the highest quality coordinates and then builds the processing network from those points The result is a set of static baselines that are derived using accurate initial coordinates status Status is every observation and set of keyed in coordinates for a point has a status field available in the Summary page of the Properties window The status can be enabled enabled as check or disabled Enabled observations and coordinates are always used by recomputation in determining the calculated position for the point Enabled as check observations and coordinates are only used if there are no Enabled ones Disabled observations and coordinates are never used stochastic model A stochastic model is a ge
3. GPS Control Point TxDOT GPS CONTROL POINT Station Name Date Adjusted Horizontal Control Dafa Monument Type Order Survey Method GPS __ TRAV__ OTHER _ City County NAD83 1993 Coordinates Convergence State Plane Grid U S Data Survey Ft Coordinates Surface Adjustment U S Survey Ft SURVEYED FROM USGS NGS MONUMENTS Latitude Longitude GEODETIC NADS3 1983 Elev Et FIELD SKETCH SIGN AND SEAL PLAT EE o E Prepared By COMPANY NAME ADDRESS PHONE Figure 6 3 Sample project specifications control point GPS User s Manual 6 8 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 3 Planning Satellite Health and Availability Only healthy satellites should be observed during the course of data collection The satellite health situation can be checked by accessing the latest GPS status message from the USCG web site at http www navcen uscg gov This status message can also determine if there were problems after the data collection period is over There are times of the day when the numbers of satellites available will vary Especially with real time kinematic RTK positioning planning a work around for these times greatly increases productivity and the quality of results Most if not all GPS software packages include a utility allowing the user to predict satellite coverage A minimum of five 5 satellites are to be logged for any GPS work In order to project satellite avai
4. This level of surveying work and points includes photogrammetric control panels boundary corners right of way ROW corners local control setup points for topographical surveys laser scan control points azimuth marks less than one half mile from the station and other points requiring similar accuracy Level 3 stations can be tied to TxDOT Level 1 network stations TxDOT Level 2 network stations or NSRS stations first order or better In some situations these points can be surveyed using any one of the GPS survey methods described herein All Level 3 points should conform to the requirements outlined in Tables 4 1 5 1 6 2 6 6 and 6 80f this manual to include the following requirements 4 e referenced to two 2 or more TxDOT Level 1 or Level 2 stations NSRS FBN or CBN published horizontal control stations located in two 2 or more quadrants relative to the survey project area post processed RTK is acceptable when done from two 2 separate base stations all new stations are established by two 2 or more independent baselines all stations must be occupied a minimum of two times baselines should have a fixed integer double difference solution any station pair used as azimuth or bearing reference for use with conventional survey measurements during the course of any other survey level should be included in a network or measured with a minimum of two independent baselines Level 3 control must be part of a geomet
5. G G Chain Link Fence G F Fence Generic G F Gate G F Noise Wail G F Picket Fence G F Post Generic G Rock Wall Fence G G Wood Fence G F Wire Fence G F Wooden Post G DRAINAGE CAN ces Figure 6 5 TxDOT Feature Codes GPS User s Manual Canal G G Catch Basin G G Concrete Channel G G Channel G G Curb Inlet G G Culvert Box G F Corrugated Metal Pipe G F Ditch Bottom Inlet G G Drop Inlet G G Ditch Pavement G G End Wall G G Flow Line G G Flume G G Flared End Section G G Stream or Tide Gauge F Gutter Inlet G G Gutter Flow Line G G Headwall Add PD G G Headwall Back G G Headwall Face G G invert Storm Sewer Goes to ZONE 3 F 6 26 Junction Box G Mitered End Section G G Culvert Pipe G F Pipe Runner Horizontal G G Pipe Runner Vertical G G Reinforced Concrete Pipe G F Rip Rap Top or Bottom G G Special Drain Features Add PD GF Storm Water Drain Line G F Safety End Treatment G G Special End Wall G G Spillway G G Storm Drain Pipe G F Structure G G Wing Wall G G Yard Drain G F TOPOGRAPHY BOT CST WEB Ditch Back G G Bank Top Bottom G G Center of Stream G G Ditch Bottom G G Ditch Top G G Earthen Dam G G Edge o
6. continued TxDOT 8 2005 Chapter 5 Network Design Section 2 Design Features Accuracy Standards for Network Baseline continued As mentioned in the Chapter 3 of this manual FBN and CBN stations are statewide GPS survey networks that form the highest order of monumented control for the NSRS These are A and B order points NGS maintained FBN stations at 100 km station spacing and volunteer densified CBN points at 25 50 km spacing are included in the Table 5 1 and serve as control for regional and local surveys Ideally the time offset between observations should be 24 hours plus 3 9 hours before the second observation in order to see a completely different satellite constellation A more practical approach for scheduling observations with a minimum of overlap is to remember that the satellite positions repeat about every 12 hours actually they advance in position about four minutes a day Scheduling with this in mind could result in substantial savings in time and cost Also it should be noted that whenever possible a different receiver should be used at that station for the repeat observation Example of a Network Design Procedure Network Design Example 1 Roughly locate both new points and existing control on a map showing roads to use in moving the observers around the project 2 From reconnaissance and mission planning software determine the best times to observe 3 For each session draw the indepen
7. zenith The zenith is the point at which a line opposite in direction from that of the plumb line at a given point on the Earth s surface meets the celestial sphere zenith angle A zenith angle is the angle measured positively from the observer s zenith to the object observed zenith delay A zenith is the delay caused by the troposphere of a GPS signal observed from a satellite directly overhead As a satellite approaches the horizon the signal path through the troposphere becomes longer and the delay increases GPS User s Manual B 30 TxDOT 8 2005 Index A A or B order stations 3 6 AASHTO Ware 7 3 accuracy of a GPS survey 1 8 2 3 algorithms 7 3 B base Error 3 7 baseline vectors 6 29 6 31 6 44 C Chi square test 6 54 classical triangulation network surveys 3 2 classification range and confidence levels 3 8 completed survey 1 8 CORPSCON 7 3 CORS Network stations 1 6 Costello Geomagnetic Index charts 6 8 D data sheet 1 4 4 7 6 4 6 35 7 3 8 2 8 3 8 5 dependent baselines 5 4 detecting blunders in a network 6 49 double difference solution 6 30 6 31 6 32 E elevation calculation 2 5 ellipsoid heights 1 6 6 56 8 4 epoch 5 3 6 37 6 47 8 4 F faststatic 6 27 6 29 6 46 feature code 6 43 8 4 field data collection 6 3 6 34 free adjustment 6 46 6 52 6 53 G geoid surface 2 5 2 6 GPS observation 1 8 2 5 3 6 6 8 6 53 GPS session 1
8. Positioning The method of faststatic rapid static positioning requires shorter occupation times than static positioning i e 15 to 20 minutes and may use a radial baseline technique network technique or a combination of the two Baseline lengths may not exceed ten 10 kilometers for L1 only receivers and twenty 20 kilometers for L1 L2 receivers Accuracy degrades at a predictable rate with this type of survey therefore longer baselines may be used when design survey quality is not needed Please refer to the manufacturer s specifications for minimum occupation times number of satellites observed and minimum amount of cycle slip free data collected for this type of data collection method FastStatic requires a least squares adjustment or other multiple baseline statistical analysis capable of producing a weighted mean average of the observations More than one base station will be used to provide redundancy for each vector FastStatic or rapid static techniques could be used for observing Levels 3 amp 4 listed in Chapter 3 Table 3 4 of this manual It provides baselines that do not exceed the maximum distances stated above in the first paragraph of this subsection GPS User s Manual 6 12 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 5 Survey Methods Post Processed Kinematic PPK Positioning Post processed kinematic survey methods provide the surveyor with a technique for high production measurements and c
9. The first is the comparison between two 2 or more measured baselines between the same two 2 stations The second is the comparison between the published baseline and the measured values Table 6 8 describes the way redundant baselines to test for validity Loop Closure Reports Running loop closures on a network of baselines is another validation check for blunders and ill fitting baselines Again Table 6 8 Pre adjustment Baseline Analysis Requirement describes several tests to run when creating and evaluating loop closures When running loop closures for any level of survey each closure must contain at least one baseline each from two 2 separate observing sessions Loop closures run around baselines from the same session containing at least one 1 dependent baseline that is an unacceptable closure for any survey performed continued GPS User s Manual 6 35 TxDOT 8 2005 Chapter 6 GPS Survey Specification Loop Closure Reports continued The table below provides tests for loop closures Table 6 8 Pre adjustment Baseline Analysis Requirements Section 7 Data Processing Level of Survey Accuracy Level 1 Level 2 Level 3 Level 4 Baseline Processing Processing Requirements M Maximum Standard Residuals in the BL Solution RMSE Redundant BL s Deviation of the Range 2cm 2cm 4cm 6cm Differences Between Repeat Unadjusted Compared Baselines Computed
10. The table below outlines requirements for network design Table 5 1 Minimum TxDOT Network Design Specifications Level of Accuracy Level 0 Level 1 Level 2 Level 3 Minimum Number of 2 2 1 0 Closest Direct CORS Ties Minimum Number of 4 4 3 25X Total FBN CBN CORS Station Ties Minimum Number of 4 4 3 2 Horizontal Station Ties Level 0 ties Level 1 or 0 Level 0 1 or 2 Minimum Number of 6 5 4 2 Vertical Ties 2 order or better Minimum Number of 2 2 2 2 Occupations Per Station Minimum Number of 50 40 30 20 Repeat BL s of all BL s Time Offset Between 4 hrs 3 hrs 2 hrs 1 hr Observations Occupations Minimum Satellite 15 Degrees 15 Degrees 13 Degrees 13 Degrees Elevation Mask Minimum Number of 4 4 3 2 Quadrants for H Station Ties Minimum Number of 4 4 4 2 Quadrants for V Station Ties Type of Ephemeris precise precise rapid or precise broadcast Required or better Level 4 5 6 and 7 surveys are generally not network surveys network requirements do not apply These should be at least be indirect ties to CORS FBN or CBN stations they may be surveyed from Level 2 stations which have been directly tied to CORS FBN or CBN stations To qualify for a new occupation the observer must remove the GPS receiver at the station and a completely new setup over that station must take place GPS User s Manual 5 5
11. coordinate system their data can be more readily compared and exchanged For this reason federal and state mapping products are referenced to two standard coordinate systems the North American Datum of 1983 NAD 83 for horizontal positions and ellipsoid heights and the North American Vertical Datum of 1988 NAVD 88 for orthometric heights Surveys are referenced to these datums through measurements to control points of the National Spatial Reference System NSRS National Spatial Reference System NSRS and Continuously Operating Reference Stations CORS The NSRS is a set of geographic point attributes that provides a consistent framework to coordinate all spatial activities The NSRS includes a nationwide network of Continuously Operating Reference Stations National CORS statewide Federal amp Cooperative Base Networks FBN CBN regional User Densification Networks UDN and other historic vertical and horizontal control Figure 2 2 illustrates the CORS Network stations in Texas and some nearby stations in adjoining states In Texas TxDOT operates the majority of CORS stations Cooperative CORS Stations Also noteworthy is the rapidly growing system of Cooperative CORS stations Links to the data from these stations are available on the NGS Web site Because of the reduced quality control QC limited hours of operation and less permanent nature of these stations it is important that the surveyor be thoroughly familiar with thos
12. particular point in the field A number of observations are done simultaneously in a session to create baselines by processing the data GPS raw data GPS raw data is the data collected by a GPS receiver for the purpose of processing at a later time GPS User s Manual B 10 TxDOT 8 2005 Appendix B Glossary GPS time GPS time is a measure of time used by the NAVSTAR GPS system GPS time is based on Universal Time Coordinated UTC but does not add periodic leap seconds to correct for changes in the earth s period of rotation GPS week A GPS week is an incremental number of weeks starting at 0 hour UTC on the date January 6 1980 April 6 1007 is the first day of GPS week 900 gravity void A gravity void is a block or area of blocks within the gravity measurement database without observations A geoid model relying upon this database would be weak and possibly in error at these blocks grid A grid is a two dimensional horizontal rectangular coordinate system such as a map projection grid azimuth A grid azimuth is measured from grid north grid conversion A grid conversion is the conversion between geographic and map projection coordinates grid coordinates Grid coordinates are the numbers of a coordinate system that designates a point on a grid grid declination The angular difference in direction between grid north and true north at any given place grid position Grid position are the gri
13. s gravity field point positions See autonomous positioning positions Positions are the place occupied by a point on the surface of the earth Positions are data that defines the location of a point with respect to a reference system postprocess Postprocess is to process satellite data on a computer after it has been collected PPM Parts per million PPM is a standardized representation of a scale error in distance measurements A 1 PPM error would result in 1 millimeter of measurement error for every 1000 meters of distance traveled precise ephemeris See ephemeris precision Precision is a measure of how closely random variables tend to cluster around a computed value High precision implies small residuals It is usually expressed as one part in or alternatively as parts per million prime meridian A prime meridian is the initial or zero median from which longitudes are reckoned At an international conference in 1884 the Greenwich Meridian was adopted by most countries as the prime meridian for the earth prime vertical A prime vertical is a vertical circle perpendicular to the plane of the celestial meridian The plane of the prime vertical cuts the horizon in the east and west points GPS User s Manual B 20 TxDOT 8 2005 Appendix B Glossary PRN Pseudorandom number 1 A sequence of digital 1 s and 0 s that appear to be randomly distributed like noise but that can be exactly rep
14. this level overseen by NGS Level 1 Statewide district wide Control Densification RRP Network Stations until recognized as NGS CORS Cooperative CORS sites Level 2 Primary Project Control Control for Airborne GPS for Photogrammetry or LiDAR Data Gathering Level 3 Photogrammetric Control Panels Boundary Corners ROW and Local Control Level 4 Wing Panels for Horizontal Positions Topography Stakeout Level 5 Sub meter Mapping for GIS includes inventory and locative surveys Level 6 1 5 Meter Mapping for GIS includes inventory and locative surveys Level 7 gt 5 Meter Mapping for GIS includes inventory and locative surveys Vertical positions for wing panels fall in Level 3 However if panel elevations have been determined by differential leveling horizontal positions if needed can be determined with Level 4 GPS observation In the interest of keeping its position information integrated properly with the NSRS TxDOT will require all new Level 1 B order densification control which is established to be referenced to a minimum of four 4 of the closest A or B order stations surrounding the station Two of these may be publicly accessible FBN or CBN stations but at least two must be CORS stations CORS stations with their downloadable data are economical to use and are the most accurate stations available The ties to the CORS FBN and CBN stations will serve as the method to determine the network accuracy co
15. F Section Corner F Cotton Spindle F Survey Station F State Border F F Traverse Turn Point F F NGS Marker Vertical Only F Vertical Panel Point Flight Point F Wing Panel Point Vertical Control F Witness Comer F Air Conditioner F F Antenna F Bench bus Stop F F Bikeway G G Billboard G F Brace Pole G Cemetery G F Cattle Guard G G Column G Faucet F Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Flag Pole F Camp Stove Grill F Handicap Ramp G F Handrail F F Incinerator F F Marsh G G Mailbox F Piling Pier G F Pit Fill G G Playground G G Parking Meter F Swimming Pool G G Pole Generic G Quarry G G Ruins F F Rock Wall G G Wail Retaining G G Satellite Dish F Septic Tank Cover F Sprinkler Head F Steps G G Wall Seawall G G Telephone Booth F Trash Disposal Dumpster F Toilet Portable F Trail G G Water Well Pump F Windmill F BUILDINGS BLD BRN G H PHSE POR ROOF SHED SIL STC Buildings Foundation Walt Etc G G Barn G G Garage G G House G G Pump House G G Porch G G Roof Tops Goes to ZONE 6 F F Shed G G Silo G G Storm Cellar F F FENCES BFN CBFN Brick Fence G G Cinder Block Fence
16. Level 1 points are to be in accordance with the following NGS publications Concrete Marks from NGS Operations Handbook and Manual of Geodetic Triangulation S P 247 Setting a Survey Disk in Bedrock or a Structure from NOAA Manual NOS NGS 1 Geodetic Bench Marks Setting a NGS 3 D Monument Based on Revised NGS 3 Dimensional 3 D Rod Mark Draft Version by Curtis L Smith National Geodetic Survey July 1996 It is recommended that new Level 2 points also follow these construction specifications but the TxDOT surveyor in charge may call for less stringent requirements Naming Convention for Level 1 and Level 2 Monuments The recommended naming convention for Level 1 and Level 2 monuments is as follows Example 1580032 Table 6 1 Naming Convention Digits Indication 158 The first three 3 digits indicate the county in which the monument was set e This is the standard county code used by TxDOT see Figure 6 5 6 6 0032 The next four digits indicate the point number of this particular monument e Itis specific for this county and there can be no duplicates in the county Some districts use variations of this by including a prefix or suffix Figure 6 2 and Figure 6 3 are sample data sheets for documenting the monuments likely to be used in the future There must be a data sheet for all Level 1 and Level 2 monuments Districts may use their own data sheet form but it must contain all the horizontal and ver
17. NMEA National Marine Electronics Association The NMEA 0183 Standard defines the interface for marine electronic navigational devices This standard defines a number of strings referred to as NMEA strings that contain navigational details such as positions NSRS National Spatial Reference System normal A normal in geodesy is the straight line perpendicular to the surface of the ellipsoid normal distribution curve A normal distribution curve is a graphical illustration of the theoretical distribution of random variables around an expected value according to probability theory It is used with histograms northing A northing is a northward reading of a grid value GPS User s Manual B 17 TxDOT 8 2005 Appendix B Glossary O observation residual An observation residual is the correction applied to an observation as determined by the adjustment observation An observation is an uninterrupted collection of GPS data at a particular point in the field A number of observations are done simultaneously in a session to create baselines by processing the data occupation time An occupation time is the amount of time required on a station or point to achieve successful processing of a GPS baseline The amount of time will vary depending on the surveying technique the type of GPS receiver used and the precision required for the final results Occupation times can vary from a couple of seconds kinematic surveys
18. Pole G Telephone Pedestal F Transformer F Tower Single Column F Power Line Underground G F Telephone Line Underground G F UTILITIES WATER WASTEWATER amp Above Ground Tank F F Easement Lines G F Filler Cap G Fire Hydrant F Gas Line G F Gas Meter F Clean Out F Gas Pump island G G Gas Pump F Gas Valve F Invert Waste Water FL ZONE 3 F Manhole Generic G Manhole Storm Drain G Manhole Wastewater G Pipe Line G F Storm Water Drain Line G F Sewage Dump Station G F Tank Cover Gas F Underground Tank Gas G F Vent Air F Valve Cover Generic F Figure 6 6 TxDOT Feature Codes continued 6 27 Valve Cover Gas F Valve Cover Water F Vent Generic F Vent Gas F Valve Generic F Vent Septic F Vent Wastewater F Water Line G F Water Meter F Water Valve F Wastewater Line G F UTILITIES SUE All Features Go To Zone 3 suc SUE Buried Cable TV F F SUCO SUE Clean Out F SUCPED SUE Cable Pedestal F SUCV SUE Casing Vent F SUE SUE Buried Electric F F SUFH SUE Fire Hydrant F SUE Buried Force Main F F SUE Buried Gas Oil F F SUE Buried Steam Petroleum F F SUE Buried Steam Petroleum F F SUE Buried Steam Petroleum EF SUE Gas Meter F SUE Gas Valve F SUE Telephone Hand hole F SUE Electric Manhole F SUE Telephone Manhole F S
19. Processing Requirements Level of Survey Accuracy Level 0 Level 1 Level 2 Level 3 Level 4 Minimum Elevation Mask in Degrees Processing 18 15 15 15 13 Use Broadcast B UltraRapid U Rapid R Precise P Ephemerides PorR P RorU P R UorB P R UorB Accuracy of WGS84 Position Held Fixed in Each BL Solution see Overview Ch 6 Sec 7 2 5m 10m 10m 10m 10m Processing Must Account for Phase Center Offsets Maximum Number of Rejected Simultaneous Phase Observations 5 10 10 10 10 This table does not apply to levels 5 7 mapping grade surveys Under certain conditions when an acceptable solution cannot be determined with the minimum elevation mask the data may include space vehicles satellites less than the minimum elevation cutoff Atmospheric Error Reduction A standard model for ionospheric group delay and tropospheric zenith delay using broadcast coefficients may be used for all baseline processing Ionospheric modeling for Ll carrier phase measurements has shown reduction in the group delay of 50 to 60 percent The remaining unmodeled error due to group delay is expected to be 1 to 2 ppm Ionospheric free processing using a linear combination of Ll and L2 carrier should be considered for baselines over 5 25km depending on the manufacturer hardware and software Follow manufacturer recommendatio
20. actual true value of the quantity being measured adjusted values Adjusted values are the values derived from observed data measurement by applying a process of eliminating errors in that data in a network adjustment adjustment Adjustment is the process of determining and applying corrections to observations for the purpose of reducing errors in a network adjustment adjustment convergence Adjustment convergence occurs when the network adjustment has met the defined residual tolerance or last ditch residual tolerance within a defined number of iterations algebraic sign An algebraic sign is a sign or associated with a value which designates it as a positive or negative number algorithm An algorithm is a set of rules for solving a problem in a finite number of steps almanac An almanac is data transmitted by a GPS satellite that includes orbit information on all the satellites clock correction and atmospheric delay parameters The almanac facilitates rapid SV acquisition The orbit information is a subset of the ephemeris data with reduced precision GPS User s Manual B TxDOT 8 2005 Appendix B Glossary ambiguity Ambiguity is the unknown integer number of cycles of the reconstructed carrier phase contained in an unbroken set of measurements The receiver counts the radio waves from the satellite as they pass the antenna to a high degree of accuracy However it has no information on the number
21. and Differences Between Known and Observed Compared Baselines Computed and y Y y y Loop Closures Baselines from Independent Observing Sessions Not Less than Loop Length Not to Exceed km 600 200 n a Required Per Project Number of Loop Closures 2 24 24 Maximum Number of Legs in any Loop 10 10 10 Maximum Misclosure for 5 Any Single Loop ppm 254 754 Maximum Average ppm Exceed cm Project Loop Misclosure 4f Maximum Misclosure in 10 Any Component Not to 16 10 507 n a This table does not apply to mapping grade Levels 5 6 and 7 GPS User s Manual 6 36 continued TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Loop Closure Reports continued Notes for Table 6 8 Data Baseline Analysis Requirements M The processing software user should follow the specifications published from the manufacturer in processing the observational data The percentage of unacceptable baselines processed within each session of data should not exceed 33 of the total number of independent baselines possible for each session If this percentage is exceeded the session should be repeated or ignored providing there is a sufficient amount of redundancy remaining in the network a Repeat baseline closures should be computed for each repeat baseli
22. and Level 2 control points It should contain information noted below Table 8 1 Control Point Data Sheets Established by contractor company Date established date monumented TxDOT Level of Survey e g Level 2 Horizontal Datum e g NAD83 Horizontal Adjustment e g 93 HARN State Plane Projection Zone e g Tx South Central 4204 Vertical datum e g NAVD88 Geoid model used e g GEOIDO3 or GEOID99 Units US Survey foot County name e g Bexar Station name e g 0150102 Latitude Latitude to 5 decimal places Longitude Longitude to 5 decimal places Northing two decimal places Easting two decimal places Ellipsoid height two decimal places Elevation two decimal places Convergence angle nearest second Elevation factor ten decimal places Combined Adjustment Factor ten decimal places Survey method for vertical GPS or leveling General location e g S Loop 1604 W 8 FM2790 To Reach description how to get to station from a well known intersection Type of Mark iron rod brass disc etc Stamping what is actually stamped on the disk Stations directly tied list up to three closest stations directly tied Sample data sheets are included in Chapter 6 Figure 6 2 and Figure 6 3 The district surveyor may have a particular preferred form to be used GPS User s Manual TxDOT 8 2005 Chapter 8
23. at a given point Also know as convergence mapping projection Mapping projection is a rigorous mathematical expression of the curved surface of the ellipsoid on a rectangular coordinate grid mask angle Cut off angle A mask angle cut off angle is the point above the observer s horizon below which satellite signals are no longer tracked and or processed Ten to twenty degrees is typical MCA minimally constrained adjustment mean sea level A mean sea level is the mean height of the surface of the ocean for all stages of the tide Used as a reference for elevations meridian A meridian is a north south line from which longitudes or departures and azimuths are reckoned minimally constrained A minimally constrained network is a network adjustment in which only enough constraints to define the coordinate system are employed It is used to measure internal consistency in observations minor axis See ellipsoid modeling Modeling is the expressing of an observation and its related errors mathematically and geometrically on some defined coordinate system such as an ellipsoid monument A monument is any object or collection of objects physical natural artificial that indicates the position on the ground of a survey station multipath A multipath is an interference that occurs when GPS signals arrive at an antenna after traveling different paths The signal traveling the longer path yields a la
24. authorized primarily military users AS is used with selective availability to deny the full precision of GPS to civilian users autonomous positioning Autonomous positioning is a mode of operation in which a GPS receiver computes position fixes in real time from satellite data alone without reference to data supplied by a base station Autonomous positioning is the least precise positioning procedure a GPS receiver can perform yielding position fixes that are precise to 100 meters horizontal RMS when selective availability is in effect and to 10 20 meters when it is not This is also known as absolute positioning and point positioning azimuth The azimuth is a surveying observation used to measure the angle formed by a horizontal baseline and geodetic north When applied to GPS observations it refers to a normal section azimuth base station A base station is an antenna and receiver set up on a known location It is used for real time kinematic RTK or differential surveys Data can be recorded at the base station for later Postprocessing In GPS surveying practice the user may observe and compute baselines that is the position of one receiver relative to another The base station acts as the position from which all other unknown positions are derived GPS User s Manual B 2 TxDOT 8 2005 Appendix B Glossary baseline A baseline is the position of a point relative to another point In GPS surveying this is the posit
25. be adjusted by least squares independently of the other survey ties continued GPS User s Manual 6 15 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Level 2 Surveys continued Primary project control network is designed to meet the following purposes provides a framework to reference the survey to a datum a mapping projection and the NSRS serves as the basis for all lower survey levels allows for the use of conventional survey equipment by always providing an azimuth or intervisible point provides control points to serve as geodetic control in a TxDOT project A well designed primary project control network will offer the surveyor more flexibility for using kinematic and RTK survey methods for the other aspects of the survey It provides an adequate amount of reference base station locations ties subsequent points together allows for expanding area of the survey and provides accurate checks throughout the survey project It may be as simple as two well placed intervisible points for use with conventional equipment All primary project control networks should be referenced tied to at least three 3 horizontal stations two of which should be the close CORS FBN CBN points Any available statewide district wide densification points qualify as holding points for the primary project control points All Level 2 networks should conform to the requiremen
26. both the base and rover points See also antenna phase correction GPS User s Manual B 19 TxDOT 8 2005 Appendix B Glossary phase difference processing Relative positioning Phrase difference processing is a computation of the relative difference in position between two points by the process of differencing simultaneous reconstructed carrier phase measurements at both sites The technique allows cancellation of all errors which are common to both observers such as clock errors orbit errors and propagation delays This cancellation effect provides for determination of the relative position with much greater precision than that to which a single position pseudorange solution can be determined picture point A picture point in surveying is a terrain feature that is easily defined on an aerial photograph Its horizontal or vertical positions have been determined by survey measurements Picture points are marked on the aerial photographs by the surveyor and are used by the photomapper plane coordinates See grid coordinates plane survey A plane survey is a survey in which the effect of the curvature of the earth is almost entirely neglected and computations of the relative positions of the stations are made using the principles of plane geometry and plane trigonometry plumbing Plumbing is the act of aligning the antenna or instrument along a vertical line plumb line perpendicular to the equipotential surface of earth
27. control points can be used to check the consistency of the adjustment and defined transformation parameters Adding additional control points builds more confidence in the calculated parameters Levels 1 and 2 do require these three 3 horizontal coordinates and four 4 elevations at a minimum In the fully constrained adjustment begin fixing the control values to determine how well the rigid network of observations fit the control Essentially the adjustment determines if the network of observations fit the network of fixed control points given some error estimate These error estimates consist of the error estimates along with the applied scalar and set up errors The transformation parameters should then be calculated to allow the observations to fit to the control continued GPS User s Manual 6 4 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Fully Constrained Adjustment continued The following fully constrained adjustments FCA for Level 1 and Level 2 should be delivered along with the listed spreadsheets or reports An FCA to determine local accuracy for horizontal positions only Submit a fully constrained adjustment fixing a minimum of three 3 horizontal stations as noted above Submit a spreadsheet or select a report showing the comparison between the MCA above and the FCA for horizontal position An FCA to determine local accuracy for orthometric heights elevations If
28. obtained using a total station or theodolite coordinates Coordinates are linear or angular quantities or both which designate the position on a point in relation to a given reference frame correlated When observations are correlated there are two or more observations or derived quantities which have at least one common source of error CORS Continuously Operating Reference Station CORS is a network of the highest quality horizontal stations forming the National Spatial Reference System and providing the public with continuous raw GPS data covariance Covariance is a measure of the correlation of errors between two observations or derived quantities Covariance also refers to an off diagonal term that is not a variance in a variance covariance matrix GPS User s Manual B 4 TxDOT 8 2005 Appendix B Glossary covariance matrix A matrix that defines the variance and covariance of an observation The elements of the diagonal are the variance and all elements on either side of the diagonal are the covariance covariant values This is the publication of the propagated computed a posteriori errors in azimuth distance and height between pairs of control points resulting from a network adjustment The term covariant indicates that this computation involves the use of covariant terms in the variance covariance matrix of adjusted control points cycle slip A cycle slip is an interruption in a receiver
29. of the type and scope of the survey and to aid in developing specifications Level 1 Surveys Level 1 is the highest order of TxDOT GPS survey It is reserved for multi project points and other statewide or district wide densification of the FBN and CBN points Since it is tied to the NSRS these marks will augment the CORS stations and will aid in control of all subsequent TxDOT survey levels The department will not usually set these on the speculation that they might be needed but usually as an adjunct to a major project Level 1 points should be established by static survey methods These points may be established at the same time as other survey levels are being performed However the points and resulting baseline vectors used in the network should be processed to derive the baseline solutions and be adjusted by least squares independently of the other survey ties The horizontal quality of these points would be comparable to first order or better conventional points and up to B order GPS quality The Level 1 points will place accurate control closer to the project shortening subsequent observation times and improving accuracy It will offer the surveyor more flexibility for using rapid static faststatic kinematic and RTK survey methods for the other aspects of the survey It provides an adequate amount of reference base station locations ties subsequent points together allows for expanding the area of the survey and provides accurat
30. of waves to the satellite at the time it started counting This unknown number of wavelengths between the satellite and the antenna is the ambiguity Ambiguity is also known as integer ambiguity or integer bias antenna height Antenna height is the height of a GPS antenna phase center above the point being observed The uncorrected antenna height is measured from the observed point to a designated point on the antenna and then corrected to the true vertical manually or automatically in the software antenna phase correction The antenna phase correction is the phase center for a GPS antenna is neither a physical nor a stable point The phase center for a GPS antenna changes with respect to the changing direction of the signal from a satellite Most of the phase center variation depends on satellite elevation Modeling this variation in antenna phase center location allows a variety of antenna types to be used in a single survey Antenna phase center corrections are not as critical when two of the same antennas are used since common errors cancel out antenna phase center Antenna phase center is the electronic center of the antenna It often does not correspond to the physical center of the antenna The radio signal is measured at the Antenna Phase Center anti spoofing AS Anti spoofing is a feature that allows the U S Department of Defense to transmit an encrypted Y code in place of P code Y code is intended to be useful only to
31. prepared to make wise on the spot decisions regarding mark identification and stability equipment use and troubleshooting and antenna setup Office personnel should be familiar with geodetic concepts and least squares adjustments Personnel should participate in any available certification and training activities All boundary control survey projects performed for TxDOT will be performed under charge of a Texas Registered Professional Land Surveyor RPLS Personnel requirements for various types of surveys may vary from one TxDOT district to another The use of certified survey technicians CST s is encouraged not to fulfill any requirements but to aid in the efficiency of operations with the use of goal oriented employees GPS User s Manual 4 5 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 3 Internet Resources Section 3 Internet Resources The CORS Site Using the CORS reference stations insures that all project control points are on a recognized network It may not seem important at the time but it also puts the TxDOT project on the NSRS at no extra cost In fact it saves sending extra people to the field and buying or renting extra GPS receivers For the extra few minutes it takes to download data the office technician may as well include several additional CORS stations beyond the one or two required by the specifications Refer to Figure 2 2 for a map of CORS stations as of this writing or visit the NGS We
32. ratio is used during initialization The receiver determines the integer number of wavelengths for each satellite For a particular set of integers it works out the probability that it is the correct set Ratio is the ratio of the probability of correctness of the currently best set of integers to the probability of correctness of the next best set Thus a high ratio indicates that the best set of integers is much better than any other set This gives us confidence that it is correct The ratio must be above 5 for new point and OTF initializations RDOP Relative Dilution of Precision real time kinematic RTK Real time kinematic is a method of GPS surveying in real time using short stop and go occupation while maintaining lock on at least 4 satellites The real time kinematic method requires a wireless data link between the base and rover receivers rectangular A rectangular are coordinates in any system in which the axes of reference intersect coordinates at right angles K reduced column K reduced column is an abbreviated version of the normal equations in which the profile equations are reordered to minimize the computer memory required to store all nonzero elements redundancy Redundancy is the amount by which a control network is over determined or has more observations than are needed to strictly compute its parts redundancy number Redundancy number is a measure of the degrees of freedom in a port
33. there are unexpected differences in the MCA and published values for vertical submit a fully constrained adjustment fixing a minimum of 4 benchmarks In many cases a fully constrained adjustment will not be required for the final elevations of a control survey If the differences between the published and measured values of the MCA holding one benchmark fixed fall within the acceptable error limits of a particular level of survey the MCA elevations will be acceptable as the final results of the survey The following subsection explains the subject in further detail Orthometric Height Determination For all levels of survey in TxDOT projects orthometric height determination must include the latest available geoid model GEOIDO3 currently Geoid models are used to compute the separations between the ellipsoid and geoid Using the latest geoid model will insure the best possible orthometric height differences between stations established by GPS methods When performing the fully constrained adjustments if multiple orthometric heights are going to be fixed then the horizontal and vertical adjustments must be done separately During the horizontal adjustment only three 3 verticals should be fixed During the vertical adjustment only two 2 horizontals should be fixed The network design process and preplanning phase is critical to avoiding the pitfalls in geoid modeling Inconsistencies in the local vertical control network due to s
34. 8 ground planes 4 3 HHARN adjustment 5 3 6 30 GPS 1 1 1 2 2006 Index horizontal and vertical constraints 5 3 I interferometric observations 2 3 L least squares adjustment 4 5 5 4 6 27 6 46 6 48 6 58 level of survey accuracy 3 5 3 7 local accuracy 3 3 5 3 6 55 M maximum relative positional error 3 7 metadata 1 4 7 2 7 3 minimum observation times 6 37 N network accuracy 1 4 3 3 3 6 3 7 6 33 network design specifications 5 4 O Office Procedures Guidelines for adjustment analysis 6 58 operational procedures 2 4 OTF initialization 6 39 P Pre adjustment Baseline Analysis 6 50 purpose of a least squares adjustment 6 52 R real time kinematic 6 7 6 8 recommended survey marker 6 18 reconnaissance survey 6 3 reporting methods of horizontal and vertical values 3 2 retrieving CORS data from NGS 4 6 RINEX 4 6 4 7 4 8 8 4 S signal to noise ratio 6 8 6 47 standards and specifications 1 2 8 3 standards of accuracy 3 2 3 5 3 8 5 4 GPS 1 2 1 2 2006 Index T two standard coordinate systems 1 6 U U S Survey Feet 7 2 GPS I 3 1 2 2006
35. Chapter 6 GPS Survey Specification Section 7 Data Processing Minimally Constrained Adjustment continued The following minimally constrained adjustments should be done for Level 1 and Level 2 surveys The required reports and or spreadsheets are listed An MCA to determine network reference accuracy Submit a minimally constrained adjustment holding the closest CORS fixed use the NAD83 CORS coordinate in latitude longitude and ellipsoid height Create a spreadsheet or select a report to compare the published CORS coordinates to the coordinates determined in the MCA An MCA to determine local HARN relationship if applicable Submit a minimally constrained adjustment holding the highest order 1 priority and most central to the project OF priority HARN station Create a spreadsheet or select a report that shows the comparison between the measured values and the published values of other HARN stations included in the survey An MCA to show the relationship of benchmarks used in the survey Submit a minimally constrained adjustment holding the highest order 1 priority highest stability monument 2 priority and most central 3 priority to the project vertical control stations Create a spreadsheet or select a report showing differences between published orthometric heights elevations and measured values The minimally constrained adjustment is an iterative process Perform the minimally constra
36. DOP of less than 6 0 GPS User s Manual TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures RTK Field Procedures Real time kinematic RTK allows close in surveying without the requirement of line of sight to the control point This is very cost effective for Level 4 surveys and with more stringent requirements RTK can be used for Level 3 surveys Set up the base station on a control point with known x y z coordinates all control points must have GPS static quality horizontal values and differential leveled vertical values The selection of the base station sites during the project planning phase will greatly affect the success of the RTK observations If a poor base station site is selected there will likely be problems throughout the entire survey The following information identifies parameters of base station sites Select a site with good sky visibility down to ten 10 degrees from the horizon Be aware of high power transmitters such as microwave TV stations military installations high voltage transmission power lines etc Be aware of multipath caused by radio wave reflective objects such as trees buildings large signboards and chain link fences etc If there are no useable control points in the immediate area or much is to be gained by setting a new control point for the base station a position can be obtained for the base station setup by means of a
37. Manual 6 9 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 3 Planning Satellite Geometry continued One way to ensure that quality data are collected for the vertical is to collect satellite data that includes at least one satellite that is tracked greater than seventy 70 degrees above the horizon However a VDOP of less than 4 0 is all that is required A PDOP of over 6 0 should probably be considered to be too great for usable data making a PDOP of over 7 0 is unacceptable Static data during periods of high DOP values should be deleted Performance of RTK is more demanding and should not be done at PDOP values of 4 or greater Space Weather Considerations A highly active ionosphere can have more severe implications for GPS observations Magnetic storms and solar radiation storms will affect the signal to noise ratio SNR and may cause initialization problems with real time kinematic RTK positioning and noisy data in static observations One measure of space weather activity is the scale developed by NOAA Their Web site address www sec noaa gov NOAAscales will predict activity on a scale of 1 to 5 with anything above one becoming a hindrance to quality data collection The Costello Geomagnetic Index charts are found at http www sec noaa gov rpc costello Kp index of five 5 or more may cause problems and GPS surveying should not be done at six 6 or above RTK should not be done at a Kp index of five 5 o
38. Project Documentation and Deliverables to TxDOT Section 3 Project Deliverables Section 3 Project Deliverables Validation Surveys On rare occasions TxDOT may require users to perform a validation survey The validation survey provides evidence that the equipment and software are able to meet the minimum standards for a given level of survey TxDOT may require this survey if the GPS equipment that is being used has not been approved tested by FGCS TxDOT may also require this survey to be performed by new users to acquaint both parties with their aptitudes for working together The validation survey should include calibration checks for mechanical and optical equipment such as fixed height tripods and tribrachs There most likely will be two 2 tests run similar to the following 1 2 Short Baseline Test Using a total station accurately measure distances along a baseline in five 5 foot increments for as many receivers as will be used on the project Set temporary points along the baseline e All of these points should be set at precisely the same elevation Use differential leveling techniques to be sure the elevations are the same e Setup all receivers at the same time and measure points using the same technique as would be used for the level of survey to be surveyed to e Occupy all of these points a second time using a different receiver setup at each point Separate the first occupation time with the second occup
39. S receiver s default file name on the line 8 digit filename A form can be tailored to the needs of the survey crew depending on their experience and proficiency The collection of weather and meteorological data may be necessary if the project worked on is to be included in the NSRS bluebooked One data sheet per observation must be turned in to the processing person This is especially true now that most receivers no longer allow for the entering of antenna heights without the use of a data collector GPS User s Manual 6 20 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Texas Department of Transportation GPS Log Sheet Operator Name Observation Date Station Name 8 digit File Name if known Antenna Height 1 measurement Meters 2 measurement Survey Ft 3 measurement Average Measured to Bottom ofnotch____ Topofnotch____ Antenna ref point Antenna Type Actual start time Actual stop time 4 digit receiver number Notes Figure 6 4 Sample GPS Log Sheet GPS User s Manual 6 2 TxDOT 8 2005 Chapter 6 GPS Survey Specification Data Collection Forms continued Section 6 Field Survey Operations and Procedures If adjustable height tripods are used the height of the antenna above the mark should be measured This measurement should take place at a minimum of three 3 locations around the ground plane in two 2 separate unit
40. TxDOT GPS User s Manual Texas Department of Transportation Revised August 2005 2005 by Texas Department of Transportation All rights reserved TxDOT GPS User s Manual August 2005 Manual Notices Manual Notice 2005 1 To Users of TxDOT Information Resources From Judy Skeen P E Director Information Systems Division Manual TxDOT GPS User s Manual Effective Date August 1 2005 Purpose To provide the Global Positioning Systems GPS information governing the operation standards used by Texas Department of Transportation TxDOT These standards are the policies and guidelines set forth by TxDOT regarding Global Positioning Systems processes and procedures The intent of this manual is for use by TxDOT employees and TxDOT consultants Development of this manual provides TxDOT employees and contractors with the concepts policies standards procedures and practices that govern Global Positioning System functions Contents This manual provides information on the use of Global Positioning System GPS technology to perform densification surveys at the State and District level down to small scale mapping projects The manual provides an index for quickly locating specific information in the field Additionally Appendix B provides a glossary for definitions of terms Supersedes The online TxDOT GPS User s Manual supersedes the TxDOT GPS Manual of Practice dated June 2004 Instructions
41. UE Meter Pole F SUE Overhead Electric F F SUE Power Pole F SUE Power Pole w Riser F SUE Sanitary Manhole F SUE Buried Storm Water F F SUE Storm Sewer Infet F SUE Storm Sewer Manhole F SUE Buried Telephone Line F F SUE Buried Telephone Line F F SUE Buried Telephone Line F F SUE Buried Fiber Optics F F SUE Telephone Pedestal F SUE Buried Water F F SUE Buried Water F F SUE Buried Water F F SUE Buried Water F F SUE Buried Water F F SUE Buried Water F F SUE Buried Water F F SUE Buried Water F F SUE Water Meter F SUE Water Manhole F SUE Water Stubout F SUE Water Valve F SUE Water Valve Box F SUE Buried Waste Water F F Indicates a LINEAR pattern Indicates a LINEAR pattern TxDOT 2K Feature Code List TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures RTK for Wing Panels Before starting to survey the panels use the rover to check into at least one other control point with known x y z coordinates all control points must have GPS static quality horizontal values and preferably differential leveled vertical values These checks should be logged in the field book and in the data collector device Also make and log checks during the course of the day If any check shots are greater than 0 10 feet horizontally or 0 12 feet vertically the problem should be r
42. Users are encouraged to print this manual double sided To ensure manual currency check the publishing date of printed manuals against the manual found on the General Services Division Online Manuals website Contact Please address your comments concerns or questions regarding this manual s information policies guidelines procedures and practices to the TxDOT Standing Committee on Surveying SCOS Copyright Notice This manual and this revision Copyright 2005 by Texas Department of Transportation Published by the Information Systems Division ISD Chapter 1 Introduction Contents Section 1 OVErVidW ccccessssssvcsccccccccsssssssscccsceecessssescsesceecaeees Section 2 Chapter Descriptions ooooconnconocnnonncoonnconnnonanonnnconnncnnos GPS User s Manual 1 TxDOT 8 2005 Chapter 1 Introduction Section 1 Overview Section 1 Overview Summary The TxDOT GPS User s Manual is referred to as the GPS User s Manual through all chapters of this manual The GPS User s Manual contains information that governs the operational standards used by Texas Department of Transportation TxDOT These standards are the policies and guidelines set forth by TxDOT regarding Global Positioning Systems GPS processes and procedures Section 2 of this chapter presents all chapter descriptions The GPS User s Manual is primarily intended to be accessed online The online version takes precedence ove
43. a curved plumb line normal to the geoid surface while the ellipsoidal and geoid heights are measured along straight lines normal to the ellipsoid surface For land surveying applications the height error associated with this approximation will always be less than one centimeter Height Component The height component of a GPS survey measurement is also affected by relatively poor geometric strength for trilateration as the earth blocks all satellite signals from the hemisphere below the horizon This imbalance makes ranging much more critical for determining vertical Slight ranging errors from multipath or atmospheric conditions are more problematic with this poor geometry Accordingly GPS height accuracies for a survey are typically 11 2 3 times worse than GPS horizontal accuracies depending on data quality and baseline length Increased redundancy of observations under independent conditions is useful for identifying errors Because of the need for four or more vertical control points and in some cases all four quadrants to establish good GPS elevations many times it will be more economical to run conventional level loops GPS User s Manual 2 6 TxDOT 8 2005 Chapter 2 Background Section 4 Coordinate Systems Section 4 Coordinate Systems Overview Many spatial activities such as navigation mapping and surveying use geographic coordinates to describe the position of objects Whenever two activities share a common
44. a form of error checking used in binary digital data storage and transfer Options for parity checking include even odd or none PDOP Position Dilution of Precision A PDOP is a unitless figure of merit expressing the relationship between the error in user position and the error in satellite position Geometrically PDOP is proportional to 1 divided by the volume of the pyramid formed by lines running from the receiver to four satellites that are observed Values considered good for positioning are small for example 3 Values greater than 7 are considered poor Thus small PDOP is associated with widely separated satellites PDOP is related to horizontal and vertical DOP by e PDOP HDOP VDOP PDOP cutoff A receiver parameter specifying a maximum PDOP value for positioning When the geometric orientation of the satellites yields a PDOP greater than the mask value the receiver stops computing position fixes PDOP mask A PDOP mask is the highest PDOP value at which a receiver will compute positions phase center See antenna phase correction phase center models Phase center models are models used to apply a correction to a GPS signal based on a specific antenna type The correction is based on the elevation of the satellite above the horizon and models electrical variations in the antenna phase center location These models are useful for eliminating errors introduced when identical antennas are not used at
45. ailable the baseline processor can calculate an inverse between the two points and derive an initialization vector This initialization vector with known baseline components is used to help solve for the integer ambiguity If the processor is able to successfully resolve this ambiguity a fixed integer solution is possible yielding the best solutions for kinematic surveys L1 L1 is the primary L band carrier used by GPS satellites to transmit satellite data Its frequency is 1575 42 MHz It is modulated by C A code P code and a Navigation Message L2 L2 is the secondary L band carrier used by GPS satellites to transmit satellite data Its frequency is 1227 6 MHz It is modulated by P code and a Navigation Message latitude 1 latitude the angular distance north or south of the equator 2 latitude in plane surveying is the amount that one end of a line is north or south of the other end As the plane coordinates of a point are known as the easting and northing of the point the latitude is the difference between the northings of the two ends of the line which may be either plus or minus least squares A mathematical method for the adjustment of observations based on the theory of probability In this adjustment method the sum of the squares of all the weighted residuals is minimized level of confidence A level of confidence is a measure of the confidence in our results expressed in a percentage or sigma level
46. ains the position information for the antenna reference point ARP and the bottom section the information for the L1 phase center of the GPS antenna It is important to use the ARP coordinates for the held position in processing The antenna type at the CORS station needed during processing is included in the header of the downloaded file In addition each section of the coordinate listing contains the ITRF position and the NAD83 position Be sure to use the NAD83 position information If the PID of a station is known the coordinates can also be found in the NGS database for the National Spatial Reference System By starting from the NGS home page click on datasheets in the five selections at the top Click on the DATASHEETS retrieval link and click on the PIDs To retrieve the appropriate data sheet key in the PID Remember there may be as many as three 3 separate data sheets associated with a station adata sheet for the monument on the ground if one exists adata sheet for the L1 phase center of the antenna the point at which data is actually collected and finally the ARP the mounting surface of the antenna Each of these points has its own PID OPUS The Online Positioning User Service OPUS is the newest addition to NGS Geodetic Tool Kit OPUS allows users to submit their GPS data files in RINEX format to NGS where the data will be processed to determine a position using NGS computers and software Eac
47. allows users to submit their GPS data files in RINEX format to NGS where the data 1s processed to determine a position using NGS computers and software Each RINEX file submitted is processed with respect to three 3 CORS sites The sites selected may not be the nearest to the users site but are selected by distance number of observations site stability etc Users have the option to select their own CORS sites The position for data will be reported back to the user via e mail in both ITRF and NAD83 coordinates as well as UTM and SPC Northing and Easting coordinates NGS OPUS Requirements OPUS is completely automatic Users are required to enter only a minimal amount of information OPUS requires the following 4 e mail address to receive results RINEX file that the user wants to process which may be selected using the browse feature antenna type used to collect this RINEX file selected from a list of calibrated GPS antennas height of the Antenna Reference Point ARP above the monument or mark that user is positioning as an option users may also enter the state plane coordinate code if they want SPC Northing and Easting Once the information is completed click the upload button to send the data to NGS User s results will be e mailed in a few minutes Upload one RINEX file at a time continued GPS User s Manual 4 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 3 Internet Resourc
48. an rotational axis of the earth and the x axis passes through 0 x N and 0 x E The y axis is perpendicular to the plane of the x and z axes fixed coordinates Fixed coordinates are point coordinates that do not move when performing a network adjustment fixed elevation A fixed elevation is an elevation obtained either as a result of tide observations or previous adjustment of leveling which is held at its accepted value in any subsequent adjustment fixed position A fixed position is an adjusted value of the position of a point on the earth The positions obtained by the adjustment are called adjusted positions and when used a control for other survey work they are called fixed positions GPS User s Manual B 8 TxDOT 8 2005 Appendix B Glossary fixed solution A fixed solution is a solution obtained when the baseline processor is able to resolve the integer ambiguity search with enough confidence to select one set of integers over another It is called a fixed solution because the ambiguities are all fixed from their estimated float values to their proper integer values flattening A flattening is a mathematical expression of the relative lengths of the major and minor axes of an ellipsoid flattening inverse A flattening inverse is an expression of the flattening that is easier to read and edit float solution A float solution is a solution obtained when the baseline processor is unable to resolve the intege
49. an be done from the Internet using the following TxDOT Web address http www dot state tx us isd gps gps htm TxDOT posts files in both RINEX and Trimble formats RINEX file naming convention is standard but a TxDOT data file in Trimble format will have a different naming convention TxDOT is in the transition of updating the GPS data distribution web page The FileFormat txt file included on the Web site will contain the latest information for naming convention and the Position_update doc contains the original TxDOT coordinates as well as antenna heights for use of the actual monument rather than the ARP Always refer to these documents when processing data from the TxDOT Web site Files in Trimble format are available in six 6 hour increments or four 4 files per day and files in RINEX format are available hourly Note that Julian dates are based on Universal Time Coordinate UTC The is no provision for combining files before download Data is kept for six 6 months and data older than six 6 months must be retrieved from NGS If all the CORS reference stations in the network the user is building are original TxDOT RRP S and if users have need for maintaining the TxDOT position used in the mid 1990s TxDOT still adjusts some of the newer RRP s to the original unchanged coordinates of that time and makes them available on the Position_update doc file above Some RRP location at the outer edges of the state may differ
50. an be used in areas with minimal obstructions of the satellites PPK uses significantly reduced observation times i e 0 5 to 3 minutes usually 10 30 seconds per point compared to static or faststatic rapid static observations This method requires a least squares adjustment or other multiple baseline statistical analysis capable of producing a weighted mean average of the observations Post processed kinematic positioning may be used for Level 4 listed in Chapter 3 Table 3 4 of this manual Real time Kinematic RTK Positioning Real time kinematic positioning is similar to a PPK or a total station radial survey RTK does not require post processing of the data to obtain a position solution This allows for real time surveying in the field and allows the surveyor to check the quality of measurements without having to process the data Real time kinematic RTK positioning may be used for Levels 3 and 4 listed in Chapter 3 Table 3 4 TxDOT Level of Survey Accuracy of this manual Level 3 surveys require that a second observation be made after losing and regaining initialization Additionally Level 3 surveys require that a second base station be set up for the purpose of creating a second baseline Most GPS units will allow the averaging or adjustment of the two or more baselines while remaining at the point Level 4 surveys however will accept the single radial baseline solution see Chapter 4 Table 4 1 Instrumentation Requirements The
51. ation time by three 3 hours After the data collection is complete process all of the baselines Compare the processed results with the designed location of the points e All stations should compare horizontally and vertically within the specifications outlined by the manufacturer and with the local positional accuracy requirements for the level of survey being worked on Long Baseline Test Take each receiver to be utilized for a given survey to a known A or B order control station with a 1 Order Class II or higher NAVD88 Adjusted Elevation and with an A or B category monument stability e Occupy this station for a minimum of two 2 hours two times with a minimum of three 3 hours separating the independent observations Repeat that process for all receivers working on a given project continued GPS User s Manual 8 6 TxDOT 8 2005 Chapter 8 Project Documentation and Deliverables to TxDOT Section 3 Project Deliverables Validation Surveys continued On completion of the data collection download the corresponding two 2 closest CORS sites to the monument s occupied e Use software to process the baselines from the CORS sites to the known monument s e Perform a minimally constrained adjustment and compare the measured location of the station s with the published values e If there are discrepancies it might be of interest to obtain an OPUS position also All stations should compare horizontally
52. atitude longitude and ellipsoidal height With the addition of a geoid height model orthometric heights can be computed Accuracy of a GPS Survey The accuracy of a GPS survey is dependent upon many complex interactive factors including observation technique used e g static vs kinematic code vs phase etc amount and quality of data acquired GPS signal strength and continuity ionospheric and tropospheric conditions station site stability obstructions and multipath satellite geometry described by the dilution of precision DOP satellite orbit used e g predicted vs precise orbits network design e g baseline length and orientation processing methods used e g double vs triple differencing etc Error Sources in a GPS Survey Error sources in a GPS survey include the following reference position errors coordinate monument stability crustal motion antenna position errors equipment setup phase center variation and offsets satellite position errors orbit ephemeris errors timing errors satellite or receiver clock errors signal path errors atmospheric delay and refraction multipath signal recording errors receiver noise cycle slips GPS User s Manual 2 3 TxDOT 8 2005 Chapter 2 Background Section 2 Surveying with GPS human errors field or office blunders computing errors processing and statistical modeling errors Operat
53. b site www ngs noaa gov under the CORS OPUS heading for an all inclusive and current map Retrieving Data from the CORS Site Retrieve CORS data from NGS from the NGS Web site at www ngs noaa gov CORS The User Friendly CORS site UFCORS allows the user to download all the data desired in just one file containing the number of hours needed from a start time entered on the online form and at the user s request can include the coordinates and ephemeris in one simple zipped download It is not necessary to convert to Universal Time Coordinate UTC time or sort through the coded file names All files available from NGS are in RINEX format Should users need to use individual hourly files a typical NGS RINEX data file from a CORS station appears with this naming convention SSSS DDD H YY T Where SSSS is the four 4 character site identifier DDD is the day of year H is a letter that corresponds to an hour long UTC time block YY is the year T is the file type Example txan3350 010 For daily files the format would be SSSS DDD H 0 YY T GPS User s Manual 4 6 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 3 Internet Resources Obtaining Coordinates from the CORS Site Coordinates for the station needed can also be found on the Web site by clicking the appropriate site on the map then choosing coordinates from the left hand menu The coordinate data sheet has two sections The top section cont
54. calibration from other control points The survey may be started on just the autonomous position after setting up the base station on the newly placed mark With a successful initialization at each of at least three 3 control points perform a forced coordinate position or calibration by keying in the proper coordinates for each point This will propagate the correct coordinates to the base station The calibration control points must be within about three 3 miles of the base and in at least two 2 separate quadrants The calibrated base station coordinates will only be as good as the quality of the chosen calibration points and are a poor substitute for the assurance of a pre surveyed control point The surveyor logs the following base station setup into the field notes station name and or number receiver and antenna type antenna measurement method i e bottom of notch bottom of antenna etc 4 record antenna H I measurements at the beginning and end of each setup e if using a fixed height tripod make and record a measurement to verify that the fixed height has been checked continued GPS User s Manual 6 23 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures RTK Field Procedures continued record the local time that the base station is started and stopped record any problems encountered during the course of the survey with the base station TxDOT VHF rad
55. cation Section 7 Data Processing Orthometric Height Determination continued When processing the data there are five 5 steps to follow for estimating GPS derived orthometric heights Table 6 10 Steps in Processing the Data Step Action 1 Perform a 3 D minimally constrained least squares adjustment of the GPS survey project i e constrain one latitude one longitude and one orthometric height value 2 Using the results from the adjustment in procedure 1 above detect and remove all data outliers The user should repeat procedures 1 and 2 until all data outliers are removed 3 Compute differences between the set of GPS derived orthometric heights from the minimally constrained adjustment using the latest National geoid model e g GEOID03 from procedure 2 above and the published NAVD 88 benchmarks 4 Using the results from step 3 of this table determine which bench marks have valid NAVD 88 height values This is the most important step of the procedure Determining which bench marks have valid heights is critical to computing accurate GPS derived orthometric heights The user should include a few extra NAVD 88 bench marks in case some are inconsistent i e are not valid NAVD 88 height values 5 Using the results from step 4 of this table perform a fully constrained adjustment holding all valid known values fixed to arrive at the resulting elevations The following table provides adjustment a
56. ch Historically this search was done using measurements collected while two or more receivers were stationary on their respective points Modern receivers and software can use the measurements collected while the roving receiver is moving Because the receiver is moving the data is described as collected On the fly OTF and the integer search using this data is an OTF search outlier An outlier is an observation which is identified by statistical analysis as having a residual too large for its estimated error The term derives from the graphical position of an observation in a histogram GPS User s Manual B 18 TxDOT 8 2005 Appendix B Glossary over determined An over determined network is a network for which more measurements have been made than are necessary to compute the coordinates of the network It is related to redundancy P code A P code is the precise code transmitted by the GPS satellites Each satellite has a unique code that is modulated onto both the L1 and L2 carrier waves The P code is replaced by a Y code when Anti Spoofing is active parallax A parallax is a change in positions of the image of an object with respect to the telescope cross hairs when the observer s eye is moved This can be practically eliminated by careful focusing parameter A parameter is an independent variable in terms of which the coordinates of points on a line or surface are given See unknowns parity Parity is
57. cified accuracy standard achievement GPS User s Manual 6 2 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 2 Specifications Section 2 Specifications Overview The specifications within this chapter ensure that a survey performed with GPS technology is repeatable meets accuracy requirements and referenced to the National Spatial Reference System NSRS by providing the following elimination or reduction of known and potential systematic error sources occupational station and observational baseline redundancy to clearly demonstrate the stated accuracy baseline processing data adjustment and data analysis to clearly demonstrate the stated accuracy documentation demonstrating verification of the results GPS survey specifications continually evolve with the advancements in equipment and techniques Changes to these specifications are expected as these advancements occur The size scope and site conditions of a project may also require variations from these specifications Remember any variations from these specifications should be designed to meet the above criteria and to achieve the accuracy standard of the survey as required by this manual All variations must be pre approved by TxDOT and documented in the project report GPS User s Manual 6 3 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 3 Planning Section 3 Planning Overview Planning is probably the most impo
58. ck Jackson Jasper Jeff Davis Jefferson Jim Hogg Jim Wells Johnson Jones Co No 130 131 66 132 133 134 135 136 137 138 139 140 141 142 145 144 145 146 147 148 149 151 152 153 154 E 5 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 County Name Karnes Kaufman Kendall Kenedy Kent Kerr Kimble King Kinney Kleberg Knox Lamar Lamb Lampasas LaSalle Lavaca Lee Leon Liberty Limestone Lipscomb Live Oak Llano Loving Lubbock Lynn Madison Marion Martin Mason Matagorda Maverick McCulloch McLennan McMullen Medina Menard Midland Milar Mills Mitchell Montague Montgomery Moore Morris Motley Nacogdoches Navarro Newton Nolan Nueces Ochiltree Oldham Orange Palo Pinto Panola Parker Parmer Pecos Polk Potter Presidio Rains Randall Co No 192 195 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 210 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 Section 3 Planning County Name Reagan Real Red River Reeves Refugio Roberts Robertson Rockwall Runnels Rusk Sabine San Augustine San Jacinto San Patricio San Saba Schle
59. code modulated onto an Ll signal C A code C A code helps the receiver compute the distance from the satellite code Code is the GPS code and is a pseudorandom noise PRN code that is modulated onto the GPS carrier signals The C A code is unclassified and is available for use by civilian applications The P code is also known and unclassified but may be encrypted for national defense purposes Code measurements are the basis of GPS navigation and positioning Code also is used in conjunction with carrier phase measurements to obtain more accurate survey quality baseline solutions CBN Cooperative Base Network CBN consists of B order stations set in cooperation with various governmental agencies for the purpose of densifying the National Spatial Reference System component A component is one of the three surveying observations used to define a three dimensional baseline between two control points The same baseline can be defined by azimuth delta height and distance in ellipsoid coordinates by delta X delta Y and delta Z in Earth Centered Cartesian coordinates and by delta north delta east and delta up in local plane coordinates GPS User s Manual B 3 TxDOT 8 2005 Appendix B Glossary constellation A constellation is a specific set of satellites used in calculating positions three satellites for 2D fixes four satellites for 3D fixes It is all of the satellites visible to a GPS receiver at one time T
60. d coordinates of a point ground control Ground control in photomapping is the control obtained from surveys as distinguished from control obtained by photogrammetric methods grid distance The grid distance is the distance between two points that is expressed in mapping projection coordinates ground distance Ground distance is the distance horizontal distance with curvature applied between two ground points ground plane A ground plane is a large flat metal surface or electrically charged field surrounding a GPS antenna used to deflect errant signals multipath reflected from the ground and other near by objects GRS 80 guard stake A GRS 80 guard stake is a stake driven near a point usually sloped with the top of the guard stake over the point The guard stake protects and its markings identify the point HDOP Horizontal Dilution of Precision height measurement A height measurement is a measuring tool supplied with an external GPS antenna and used rod for measuring the height of the antenna above a point GPS User s Manual B 11 TxDOT 8 2005 Appendix B Glossary H I Height of instrument H I is synonymous with antenna heights for GPS histogram A histogram is a graphical display of the size and distribution of residuals in a network adjustment horizontal datum In plane surveying the grid system of reference used for the horizontal control of an area defined by the easting and nor
61. datum A level datum is a level surface to which elevations are referred The generally adopted level datum for leveling in the United States is mean sea level For local surveys an arbitrary level datum is often adopted and defined in terms of an assumed elevation for some physical mark bench mark level net Level net are lines of spirit leveling connected together to form a system of loops or circuits extending over an area Level net is also called a vertical control net GPS User s Manual B 14 TxDOT 8 2005 Appendix B Glossary level of significance A level of significance is an expression of probability A one sigma standard error is said to have a level of significance of 68 percent For one dimensional errors a 95 percent level of significance is expressed by a 1 96 sigma and a percent level of significance is expressed by a 2 576 sigma local ellipsoid A local ellipsoid is the ellipsoid specified by a coordinate system The WGS 84 coordinates are first transformed onto this ellipsoid then converted to grid coordinates local geodetic coordinates A local geodetic coordinate is the latitude longitude and height of a point The coordinates are coordinates expressed in terms of the local ellipsoid local geodetic A local geodetic is at any point a plane at the ellipsoid height of a given point which is horizon parallel to the tangent plane to the ellipsoid at that point Coordinate values for the local ge
62. dent baselines chosen to be observed on map Move through the project until all points have been observed 4 Observing the rules for time differences plan the repeated occupations and observations Consider redundancy requirements 5 Measure and record antenna height in two different units at the beginning and before the end of each session 6 Fill out observation sheet each session 7 Every one moves every session where practical GPS User s Manual 5 6 TxDOT 8 2005 Chapter 6 GPS Survey Specification Contents Section 1 Ovev Wasted 6 2 Section 2 PEC CAOS eo 6 3 Section Plannin yy Oe ea cle CON Lhe iG rs eo 6 4 SCG A aan een ae adeno ate eae 6 11 Section 5 Survey Methods cds iris 6 12 Section 6 Field Survey Operations and Procedures oooooocccnoncccnocccononccnnnnccnnnnccnnnnccnnnnoss 6 14 Section Da PTO CS SSL IN acti ic os I Sel cle Ge glide acca we Ride vas a esc dupe saan 6 29 GPS User s Manual 6 1 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 1 Overview Section 1 Overview Scope The specifications outlined in this chapter cover the planning of the project field data acquisition methods field survey operations and procedures monumentation survey methods data processing analysis of the data and documentation The uses of these specifications along with the manufacturer s specifications provide a means for the surveyor to evaluate the survey and to verify the spe
63. e checks throughout the survey project All Level 1 points should be referenced tied to at least four 4 FBN CBN CORS stations two 2 of which should be CORS stations continued GPS User s Manual 6 14 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Level 1 Surveys continued The current national reference datum is the North American datum of 1983 TxDOT places all new projects on this datum and it is recommended that the HARN adjustment noted by NAD83 2003 be used Be sure the adjustment specified by the district survey coordinator is used some situations dictate previously used datum adjustments All Level 1 points should conform to the requirements outlined in Tables 4 1 5 1 6 2 6 6 and 6 8 of this manual to include the following requirements referenced to at least the two 2 closest CORS control stations located in two quadrants relative to the survey project area and additional FBN or CBN published horizontal control stations for a total of at least 4 stations one or more in each of at least three 3 of the quadrants of the project area referenced to five 5 or more published vertical control stations of second order or better located in all four 4 quadrants relative to the survey project area if vertical is required for the survey all new stations are established by two 2 or more independent baselines all stations must be occu
64. e chi square test of network error estimates degrees of freedom and level of confidence will pass At this point there is confidence that the network observations are working together and that there are no large errors remaining in the network Once the minimally constrained adjustment has been completed move on to the fully constrained adjustment to fit the observations to the local control datum Fully Constrained Adjustment The fully constrained adjustment FCA transforms the network of observations to the control points in the network Once the network is fixed to those control points adjusted coordinates based on the project datum using the appropriate datum adjustment as recommended by TxDOT for all other points in the network can then be determined Use this step to check that the existing control fits together well The minimally constrained adjustment MCA showed that the observations fit together and a fairly rigid network is defined It is assumed that if any large errors are present in the fully constrained adjustment the source is non homogeneous control points values Any ill fitting control points should not be fixed constrained When designing the network it is good practice to use a minimum of three 3 horizontal control points and four 4 vertical control points because two 2 horizontal and three 3 vertical control points are required to define transformation parameters The additional horizontal and vertical
65. e stations in their own area before depending on them Also note that Cooperative CORS coordinates are less accurate than CORS coordinates GPS User s Manual 2 7 TxDOT 8 2005 Chapter 2 Background Section 4 Coordinate Systems CORS 2005 GDAC n HLK a velo n N OKCL TXAM a e PRCO o Sum n OKAD n OKLW ox TAS pa KAN Dea WY n A et Ln FPR gente TXLU d qe Ss NMRO a n TXDE Txco JTNT oe s KaD Ana TM WSMN e DES e SHRV n e par a enna TxD PATT 1NSU Spa s von TWA n N S es e JXLF N e ESV y n o Mey MOO1 pu pes BY L Pra e X XSN MFR THC g TXCN ci ore e Pes aT ar xu a a q TXHU my TXPE rr be x P3 Says Legend 1 CORS TxDOT 0 125 250 500 Miles a p a CORS not TxDOT L f fi f L f heat i A Figure 2 2 CORS Stations FBN and CBN Federal Base Network stations FBN 75 to 125 km spacing or Cooperative Base Network CBN stations 25 to 30 km spacings are B order accuracy and make up the HARN network These HARN stations have been observed using GPS and have been either used previously as reference stations in the adjustment of the old conventionally surveyed federal monuments or they are newly placed monuments There are about four hundred of these listed by NGS in Texas continued GPS User s Manual 2 8 TxDOT 8 2005 Chapter 2 Background Section 4 Coordinate Systems FBN and CBN con
66. ecifications on technical reports digital data control point data sheets and validation surveys are presented Appendix A References Appendix A contains a comprehensive list of references used in the preparation of this manual Appendix B Glossary Appendix B contains extensive GPS survey related terms and definitions Hyperlinks Hyperlinks in this manual may appear as red underlined text or as Web addresses These hyperlinks take the reader to related information found within this manual another manual or outside the TxDOT Manual System GPS User s Manual 1 5 TxDOT 8 2005 Chapter 1 Introduction Section 2 Chapter Descriptions How to Get Help The district survey coordinators are available to answer questions and discuss procedures and specifications outlined in this manual Additionally the Information Systems Division provides a helpdesk number which offers survey help from the Automated Survey Support Unit Users may access the helpdesk by calling 512 302 2350 press 3 for engineering support and then 4 for surveying support As GPS technology advances changes in the manual will be necessary If there is a need for updates or corrections please notify the district survey coordinator TxDOT employees will also be able to find contact information for an area SCOS representative on the intranet Web site crossroads under the miscellaneous link TxDOT Surveying and Mapping Printing Please print double sided
67. ects the code signal ionospheric modeling lonospheric modeling is the time delay caused by the ionosphere varies with respect to the frequency of the GPS signals and affects both the L1 and L2 signals differently When dual frequency receivers are used the carrier phase observations for both frequencies can be used to model and eliminate most of the ionospheric effects When dual frequency measurements are not available an ionospheric model broadcast by the GPS satellites can be used to reduce ionospheric affects The use of the broadcast model however is not as effective as the use of dual frequency measurements iteration An iteration is a complete set of adjustment computations that includes the formation of the observation equations normal equations coordinate adjustments and computation of residuals GPS User s Manual B 13 TxDOT 8 2005 Appendix B Glossary K K reduced column K reduced column is an abbreviated version of the normal equations in which the profile equations are reordered to minimize the computer memory required to store all nonzero elements kinematic surveying Kinematic surveying is a method of GPS surveying using short Stop and Go occupations while maintaining lock on at least 4 satellites It can be done in real time or postprocessed to centimeter precisions known point initialization A known point initialization is used in conjunction with kinematic initialization If two known points are av
68. ed and accessed electronically The manual is divided into an introductory chapter and chapters that address specific GPS topics Table 1 1 TxDOT GPS User s Manual Organization Element Purpose Chapter 1 Identifies and provides manual information and organization Additionally it identifies the authorities laws and standards that govern the manual Chapters 2 8 Provide TxDOT GPS policies and procedures Appendix A References Appendix B Glossary GPS User s Manual 1 3 TxDOT 8 2005 Chapter 1 Introduction Section 2 Chapter Descriptions Section 2 Chapter Descriptions About this Section The following subsections describe the contents of Chapters 2 8 of the GPS User s Manual The hyperlinks found in this section will lead the reader to the Overview section of a chapter Chapter 2 Background Chapter 2 provides background on surveying with GPS including accuracy error sources and the process for handling errors It presents information on surveying vertical networks with GPS and the basic differences of conventional and GPS methods Chapter 3 Accuracy Standards Chapter 3 discusses local and network accuracy and provides information on the concepts guidelines standards and specifications as well as methodologies associated with GPS survey accuracy standards Additionally it provides tables to illustrate coordinate tolerances and historical accuracy Chapter 4 Equipment and Re
69. edures and practices that govern Global Positioning System GPS functions It is not the intention of this manual to document all technical procedures used within the department Scope This manual provides guidance to the surveyor in the use of GPS technology to perform densification surveys at the state and district level down to small scale mapping projects It sets out the criteria and specifications for TxDOT and consultant surveyors to follow Organization of Chapters Chapters 2 8 are similar in organization and address a general aspect of GPS surveying and related information Each chapter has a chapter overview numbered sections for major topics unnumbered subsections describing concepts and policies relevant to the section topic Some chapters also contain procedures with step by step directions for successfully completing tasks related to the section topic Subsequent sections are numbered sequentially within each chapter and contain related information associated with the chapter topic Each chapter is titled to describe its content Subsections contain detailed information that describes concepts policies standards and procedures related to the section topic Concepts and policies a user needs to know to successfully complete a procedure are presented before the procedure and procedures are presented in tables with step by step step action directions for completing a task This manual is designed to be publish
70. ensky datum grid multiple regression Datum grid multiple regression are datum transformations usually convert data collected in the WGS 84 datum by GPS methods onto datums used for surveying and mapping purposes in individual regions and countries de correlate To de correlate is to remove the covariances between observations This may be done through elaborate orthogonal transformations or by computing separate horizontal and vertical adjustments GPS User s Manual B 5 TxDOT 8 2005 Appendix B Glossary deflection of the vertical A deflection of the vertical is the angular difference between the upward direction of the plumb vertical line vertical and the perpendicular normal to the ellipsoid degrees of freedom Degrees of freedom is a measure of the redundancy in a network delta elevation Data elevation is the difference in elevation between two points delta N delta E Delta N and delta E are coordinate differences expressed in a Local Geodetic Horizon delta U coordinate system delta X delta Y delta Z Delta X Y and Z are coordinate differences expressed in a Cartesian coordinate system differential positioning Differential positioning is the precise measurement of the relative position of two receivers that are tracking the same satellites simultaneously discrepancy 1 Discrepancy is the difference between duplicate or comparable measures of a quantity 2 Discrepancy is the d
71. ents on survey tripods tribrach centering errors Tribrach centering errors are errors associated with centering plumbing the tribrach over errors the observed point These errors are estimated The estimate is based on surveying the quality of surveying methods and should be conservative turning points Turning points are temporary points of known elevation tropo correction Tropospheric correction Tropo correction tropospheric correction is the correction applied to a satellite measurement to correct for tropospheric delay tropo model Tropospheric model A tropo model occurs when GPS signals are delayed by the troposphere The amount of the delay will vary with the temperature humidity pressure height of the station above sea level and the elevation of the GPS satellites above the horizon Corrections to the code and phase measurements can be made using a tropo model to account for these delays GPS User s Manual B 27 TxDOT 8 2005 Appendix B Glossary U UDN User Densification Network A UDN is a station set by the public that have been bluebooked by the NGS for the purpose of providing additional control stations adjusted to the National Spatial Reference System univariate Univariate is a mathematical function describing the behavior of one dimensional random errors in angle distance difference in height elevation e gt gt o ellipsoid height universal time Universal ti
72. es NGS OPUS Requirements continued Read through each of the OPUS Help Links It is important that users understand how to correctly submit their data and how to interpret the results For inquires or comments use the OPUS e mail button OPUS is intended for use in the conterminous U S Alaska and Hawaii It is NGS policy not to publish geodetic coordinates outside the U S without the agreement of the affected countries Useful Web Sites Below is a list of Web site addresses which may be accessed for further information regarding GPS related activities Click the hyperlink to access the Web site for the following GPS Antenna Information GPS Orbital Data GPS Overview National Geodetic Survey NGS Data Sheets NGS CORS Data NGS PC Software OPUS Space Weather TxDOT RRP Data USCG GPS User s Manual http www ngs noaa gov ANTCAL index shtml http www ngs noaa gov GPS GPS html http www colorado edu geography gcraft notes gps gps_f html http www ngs noaa gov http www ngs noaa gov cgi bin datasheet prl http www ngs noaa gov CORS http www ngs noaa gov PC_PROD pc_prod shtml http www ngs noaa gov OPUS http www sec noaa gov today html http www dot state tx us isd gps gps htm http www navcen uscg gov 4 9 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 3 Internet Resources Retrieving Data from TxDOT Retrieving CORS data from the original TxDOT maintained stations RPS s c
73. esolved Wing panel surveys are in the Level 3 category and must therefore adhere to those requirements including positioning from a second base station However on occasion the elevations are derived from spirit leveling from the control but horizontal is still asked for In this case a Level 4 RTK survey is acceptable RTK for Topographical Surveys Connectivity of survey chains is required for topographical surveys and the use of TxDOT feature codes is mandatory This TxDOT list is available in Trimble format as txdot2k fcl see Chapter 8 Digital Data and in CAiCE format as txdot2k ftb A printed list of the TxDOT feature codes is available and is shown in Figure 6 5 and Figure 6 6 At no time should the rover exceed a distance of three 3 miles from the base in a topographical survey using radial baselines With RTK topographical surveys any time initialization is lost and reestablished a previously occupied point should be redone as a check At least one in every ten 10 points of the survey should be redone with a new initialization at a later time This would result in a total of at least 10 of the stations receiving a second occupation GPS User s Manual 6 28 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Section 7 Data Processing Overview In the scope of these specifications GPS data processing includes the review and cataloging of collected data files processing phase measureme
74. etween the time of signal reception measured in the receiver time frame and the time of emission measured in the satellite time frame Pseudorange is obtained by multiplying the apparent signal propagation time by the speed of light Pseudorange differs from the actual range by the amount that the satellite and receiver clocks are offset by propagation delays and other errors including those introduced by selective availability pseudostatic GPS Pseudostatic GPS also known a pseudo kinematic and repeat occupation is a relative positioning technique which relies upon two or more simultaneous observations at a point pair separated by some time interval typically 60 minutes or more in order to solve the integer bias terms from the change in satellite geometry occurring between the repeat observations GPS User s Manual B 21 TxDOT 8 2005 Appendix B Glossary Q quality acceptance test A quality acceptance test is one or more software evaluation tests performed on raw GPS measurement data to determine if the data passes or fails a set of tolerance values that the user defines These tests either remove data from further processing or mark data requiring quality improvements QC records Quality Control records QC records are used with precise positioning applications This receiver option allows a user to process RTCM 104 corrections and satellite data in real time to provide position precision statistics ratio A
75. f Land Management New Mexico State Office Accuracy Standards for Cadastral Surveys New Mexico State Office U S Bureau of Land Management Vorhauer Maralyn L 1998 Adjusting NGS Data March Page 26 31 Point Of Beginning Business News Publishing Company Wisconsin Department of Transportation 1996 Guidelines on Standards and Specifications For Global Positioning System Surveys in Support of Transportation Improvement Projects January Draft Technical Services Geodetic Surveys Unit Madison WI West Virginia Department of Transportation 2000 Technical Guidelines for GPS Control Surveys Zilkoski David B 2000 The GPS Observer November Page 24 Point Of Beginning Business News Publishing Company GPS User s GuideManual A 4 TxDOT 8 2005 Appendix B Glossary Introduction This appendix contains the definitions of most but not all GPS related terms The terms and their descriptions below are explained as used intended in the context of this manual Other or more elaborate descriptions may exist for the terms listed 1 sigma 1 sigma is one standard error from the mean a posteriori errors A posteriori errors are the a priori errors multiplied by the standard error of unit weight reference factor resulting from a network adjustment a priori errors A priori errors are the errors estimated for observations prior to a network adjustment accuracy Accuracy is the closeness of a measurement to the
76. f Water G F Footing Conc For Signs G G Grade Break G G High Point G Levee G G Low Point G Miscellaneous Line Add PD G G Miscellaneous Point No Code Add PD G Natura Ground G G Path G G Ridge Line G G Spot Elev Generic Also see NG 6 Slope Bottam G G Slope Top G G Sidewalk G G User Defined Point or Line Add PD L U User Defined Point or Line Add PD U U User Defined Point or Line Add PD U U Water Elevation G F Web Wall Goes to ZONE 1 G G ROADWAY ABUT DSN Bridge Abutment Goes to Zone 1 G G Attenuation System G G Asphalt G Bridge Approach Slab Zone 1 G G Baseline Also see CL F F Drilt Cores Test Holes F Concrete Traffic Barrier Temp FE a Curb Cut Ramp G G Center Line G G Concrete Pavement G G Center of Road Crown G G Curb Back G G Concrete Traffic Barrier Permanent G G Dirt Road G G Driveway Pd Type G G Sign Double Support Add Width as PD F ROADWAY Continued EC ECPV EG EP Edge of Concrete G G Edge of Concrete Paving G G Edge of Gravel G G Edge of Pavement G G continued TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Rover Initialization Figure 6 5 TxDOT Feature Codes contin
77. for horizontal ellipsoid height and orthometric height is as follows Table 3 3 FGDC Accuracy Standards Accuracy Classification 95 Confidence 1 Millimeter 0 001 meters 2 Millimeter 0 002 meters 5 Millimeter 0 005 meters 1 Centimeter 0 010 meters 2 Centimeter 0 020 meters 5 Centimeter 0 050 meters 1 Decimeter 0 100 meters 2 Decimeter 0 200 meters 5 Decimeter 0 500 meters 1 Meter 1 000 meters 2 Meter 2 000 meters 5 Meter 5 000 meters 10 Meter 10 000 meters TxDOT Standards TxDOT has numerous survey accuracy requirements based on the type of project being surveyed Listed in the table below are seven levels with typical types of surveys for each The level of survey accuracy will be used as a standard throughout this manual to define the quality of the survey measurements for a particular application The seven levels of course are of equal or less accuracy than the A and B order federal monuments which could be considered Level 0 in the TxDOT scheme A Level 0 is shown in some of the charts only to show the relationship of the NGS points to the seven TxDOT levels GPS User s Manual 3 6 continued TxDOT 8 2005 Chapter 3 Accuracy Standards Section 3 Local and Network Accuracy TxDOT Standards continued Table 3 4 TxDOT Level of Survey Accuracy TxDOT Level of Accuracy Typical Applications Level 0 CORS FBN CBN
78. from the NGS positions epoch 2002 by a couple of centimeters Remember to us H I s when holding the actual monument rather than the usual ARP position Also note that these H I s are to the phase center of the antenna GPS User s Manual 4 10 TxDOT 8 2005 Chapter 5 Network Design Contents Section 1 OVErViICW ccccsssssevsecccccccesssescsccccceeeeessssscccecceessssevess Section 2 Design Feat r S datan iaa GPS User s Manual 5 1 TxDOT 8 2005 Chapter 5 Network Design Section I Overview Section 1 Overview Summary Network design includes 1 the determination of the number and location of existing control stations for network constraints 2 the selection of new project control stations and 3 the relative dispersion of network observations Network design has relevance for concerns regarding the elimination and or reduction of potential error sources as well as for providing adequate ties to the existing geodetic reference system NAD83 These concerns may be addressed by the choice of which existing control stations should be included as well as the planning of the new station locations and network observation periods GPS derived orthometric heights are particularly sensitive to the distribution of observations and network constraints GPS User s Manual 5 2 TxDOT 8 2005 Chapter 5 Network Design Section 2 Design Features Section 2 Design Features Control To meet a ne
79. ght Determination continued There are three 3 general requirements for establishing GPS derived orthometric heights on TxDOT projects Table 6 9 GPS Derived Orthometric Requirements Project vertical control will require the fixing of a geoid model for determining elevations with GPS surrounds the project with valid NAVD 88 bench marks i e minimum number of stations is four 4 for Levels 3 and above one in each corner of project users may have to extend well outside the project area to do this maybe even run an additional level loop level 4 surveys are generally RTK and baseline distances kept under 10 kilometers are short enough that geoid undulation can be dealt with by using the most recent NGS Geoid model to determine elevations during data collection from a base station with valid orthometric height at the TxDOT surveyor s discretion very confined RTK work within less than a couple of kilometers may not require the use of a geoid model if the base station has a valid orthometric height For large project areas there should be no points set farther than 20 kilometers of an occupied first or second order benchmark or previously set GPS benchmark For projects located in mountainous regions occupy valid bench marks at the base and the summit of mountains even if distance is less than 20 km continued GPS User s Manual 6 44 TxDOT 8 2005 Chapter 6 GPS Survey Specifi
80. h RINEX file submitted is processed with respect to three 3 National CORS sites or Cooperative CORS sites Any stations in a TxDOT network that contain two 2 or more hours of raw GPS data can be processed at this Web site The tie sites selected may not be the nearest to the users site but are selected by distance number of observations site stability etc Users have the option to select their own CORS sites The ITRF and NAD83 coordinates as well as Universal Transverse Mercator UTM and SPC Northing and Easting report position data back to the user via e mail continued GPS User s Manual 4 7 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 3 Internet Resources OPUS continued TxDOT recommends that users check the results of the processing and adjustment on new points with this NGS service As a minimum at least one station should be checked in every network OPUS positions are usually within one or two tenths of a foot However they may be less precise in areas of one direction only ties Use this to verify the NAD83 HARN position and ellipsoid height Orthometric heights may not tie based on whether the elevation was established before or after the original Texas HARN network was created NGS Description of OPUS The National Geodetic Survey operates the Online Positioning User Service OPUS as a means to provide GPS its user s easier access to the National Spatial Reference System NSRS OPUS
81. he best choice For baselines greater than 40 kilometers but less than 200 kilometers a session may consist of a set of partially fixed integers and may also include float solutions where no integers could be fixed For baselines greater than 200 kilometers the final solution should be an ionospheric free ambiguity float L1 L2 solution In all cases the user should refer to their manufacturer specifications if conflicts exist within the section of the specifications The quality of acquired data should be determined from the double difference residual plots and the RMSE values Final coordinates and their quality assessment should be determined by loop closure analysis least squares adjustment analysis of repeated baselines and free adjustment residuals Troubleshooting Problematic Baselines A problematic baseline can be defined as a line observed with two carrier phase GPS receivers L1 or L1 L2 and the baseline solution does not meet the manufacturer s specification for quality For short lines determined to need a double different fixed solution or for longer lines other solutions are acceptable as specified in Table 6 8 In most cases the problematic baseline was observed with enough satellites for a long enough time period but the quality indicators show the line to be unacceptable The first thoughts may be to re observe the line However this should be the user s last resort There are enough tools available in the baseline pr
82. he optimum constellation is the constellation with the lowest PDOP See also PDOP constrained Constrained is a way to hold fix a quantity observation and coordinate as true in a network adjustment constraint Constraint is external limitations imposed upon the adjustable quantities observations and coordinates in a network adjustment contour line A contour line is an imaginary line on the ground all points of which are above or below a specified datum contour interval A contour interval is a predetermined difference in elevation vertical distance at which contour lines are drawn The contour interval is usually the same for maps of the same scale contour map A contour may is a map that portrays relief by means of contour lines control A control is a system of points whose relative positions have been determined from survey data control point A control point is a point whose position horizontal or vertical has been determined from survey data It is used as a base for a dependent survey control stations Control stations are stations whose position horizontal or vertical has been determined from survey data and is used as a base for a dependent survey control survey A control survey is a survey that provides positions horizontal or vertical of points to which supplementary surveys are adjusted conventional observation A conventional observation is an observation in the field
83. icher Scurry Shackelford Shelby Sherman Smith Somervell Starr Stephens Sterling Stonewall Sutton Swisher Tarrant Taylor Terrell Terry Throckmorton Titus Tom Green Travis Trinity Tyler Upshur Upton Uvalde Val Verde Van Zandt Victoria Walker Waller Ward Washington Webb Wharton Wheeler Wichita Wilbarger Willacy Williamson Wilson Winkler Wise Wood Yoakum Young Zapata Zavala Figure 6 1 List of the standard county designator codes used by TxDOT GPS User s Manual TxDOT 8 2005 Chapter 6 GPS Survey Specification Control Point Data Sheet Form Texas POINT NAME Department of Transportation LOCAL NAME if any December 2004 HORIZONTAL NAD83 93 Geodetic Latitude Longitude STATE PLANE Northing Easting State Plane Zone Scale Section 3 Planning Mapping Angle Combined Factor SURVEYED FROM a b c INTERVERSIBLE POINT NAME AZIMUTH amp DISTANCE TO INTERVISIBLE POINT NAVD83 ELEVATION Conventional 3 wire leveling GPS from at least three 2 order or better benches GEOID___ GPS from 3 order or less benches GEOID___ SURVEYED FROM a b c HISTORY DATE ACTIVITY TYPE OF MARK Description Publicly Accessible Yes No GPSable Yes Marginally DESCRIPTION DATE FROM TO Figure 6 2 TxDOT Control Point Data Sheet No GPS User s Manual 6 7 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 3 Planning
84. icient occupational and observational redundancy to clearly demonstrate the stated accuracy adequate baseline processing and evaluation network least squares adjustment and data evaluation sufficient documentation to allow verification of the results Terminology In dealing with GPS equipment manufacturers federal agencies and long time surveyors we find phrases and terminology used in different and confusing ways For the purpose of this manual a GPS observation is an uninterrupted recording of satellite data at one station and the created file of raw data A GPS session is a number of observations run simultaneously for creating baselines GPS User s Manual 3 12 TxDOT 8 2005 Chapter 4 Equipment and Resources Contents Section Overview ui akdnndieuena nha ea ei adi 4 2 Section 2 A Ome atamaseagaanl EN 4 3 Section 3 mt rnet RESOURCES ocio SSA o eases 4 6 GPS User s Manual 4 TxDOT 8 2005 Chapter 4 Equipment and Resources Section I Overview Section 1 Overview Summary This chapter presents valuable information regarding the use of GPS instruments and equipment It includes discussions on the requirements for accurate and consistent data collection for a variety of instruments and equipment Basic instrumentation for TxDOT GPS control surveys includes multiple sets of receivers antennas and fixed height and or variable height tripods To minimize equipment biases use of ide
85. ifference between computed values of a quantity obtained by different processes in the same survey DOP Dilution of Precision DOP is an indicator of the quality of a GPS position It takes account of each satellite s location relative to the other satellites in the constellation and their geometry in relation to the GPS receiver A low DOP value indicates a higher probability of accuracy Standard DOPs for GPS applications are PDOP Position three coordinates HDOP Horizontal two horizontal coordinates VDOP Vertical height only TDOP Time clock offset only doppler shift A doppler shift is the apparent change in frequency of a signal caused by the relative motion of satellites and the receiver double differencing Double differencing is an arithmetic method of differencing carrier phases simultaneously measured by two receivers tracking the same satellites This method removes the satellite and receiver clock errors DTM Digital Terrain Model DTM is a representation in graphic form on the computer of the terrain through the area being surveyed dual frequency A dual frequency is a type of receiver that uses both L1 and L2 signals from GPS satellites A dual frequency receiver can compute more precise position fixes over longer distances and under more adverse conditions because it compensates for ionospheric delays GPS User s Manual B 6 TxDOT 8 2005 Appendix B Glossary E easting Easting is a
86. ights Ellipsoid Measurements In contrast GPS measures the relative heights of points above a smooth mathematically simple surface called an ellipsoid An example of an ellipsoidal reference surface is GRS80 the defining ellipsoid for NAD 83 Elevations derived from GPS measurements are ellipsoidal heights minus the separation between the geoid and ellipsoid The ellipsoidal h and orthometric H heights are closely related by the geoid height N the separation between the two reference surfaces as shown in Figure 2 1 below Geoid heights can be derived from GPS observations on bench marks where both the ellipsoidal and orthometric heights have been measured for the same point A network of GPS bench mark observations gravity observations and elevation models are used to develop a geoid model From this model geoid heights at other points in the area can be estimated The accuracy of these geoid heights is dependant upon the accuracies of the various measurements used to construct the model ay Ce eS Figure 2 1 Relationship between ellipsoidal h orthometric H and geoid N heights GPS User s Manual 2 5 TxDOT 8 2005 Chapter 2 Background Section 3 Surveying Vertical Networks with GPS Note that in the continental United States the ellipsoid is above the geoid therefore N in Figure 2 1 is negative Also note that the height equation h H N is only an approximation as the orthometric height is measured along
87. ined adjustment to check the observations for internal consistency and estimates errors for all observations If bad observations are found they should appear as outliers in a histogram of standardized residuals If bad observations are discovered they should be removed one at a time starting with the largest so that the statistics of the network are not skewed An adjustment should then be performed again Errors are estimated again In the subsequent adjustments the estimated error may be rescaled to produce more realistic error estimates These procedures should be repeated until the results meet the following conditions all outliers have been removed from the network observations have the most accurate error estimates possible and observations are adjusted such that they fit together well continued GPS User s Manual 6 40 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Minimally Constrained Adjustment continued During the iteration process two least squares statistics should be used to gauge progress Reference factor The reference factor shows how well the observations along with their respective error estimates are working together Once the reference factor approaches 1 00 the errors in the observations are properly estimated and all observations have received their appropriate adjustments Chi square test Typically when the reference factor approaches 1 00 th
88. ing GPS Relative Positioning Techniques Version 5 0 reprinted with corrections August 1 1989 National Geodetic Survey National Oceanic and Atmospheric Administration Silver Spring MD Federal Geodetic Control Subcommittee Federal Geographic Data Committee 1998 Geospatial Positioning Accuracy Standards Reston VA F DC STD 007 1998 Federal Geographic Data Committee 1998 Part 1 Reporting Methodology Geospatial Positioning Accuracy Standards FGDC STD 007 1 1998 Federal Geographic Data Committee Washington DC Federal Geographic Data Committee 1998 Part 3 National Standard for Spatial Data Accuracy FGDC STD 007 3 1998 Geospatial Positioning Accuracy Standards Federal Geographic Data Committee Washington D C Federal Geographic Data Committee 1998 Part 6 Point Profile Spatial Data Transfer Standard FGDC STD 002 6 Federal Geographic Data Committee Washington D C FGCC Bossler 1984 Standards and Specifications for Geodetic Control Networks September GPS User s Guide A I TxDOT 8 2005 Appendix A References FGDC 1998 Geospatial Positioning Accuracy Standards Parts 1 and 2 Fiedler Jerry 1992 Standards for GPS Cadastral Control Surveys using Relative Positioning Techniques Bureau of Land Management Branch of Cadastral Survey Development Service Center Floyd Richard P 1978 Geodetic Bench Marks NOAA Manual NOS NGS 1 National Oceanic and Atmospheric Administration Rockville MD Foote Ken
89. inimum Number GPS Receivers 3 3 3 2 2 Photo or Pencil Rubbing Required for all Stations Except CORS Y Y N N N M denotes Manufacturer recommended value Measurements to be divided between beginning and end of session Measurements should be made in two different units Minimum of receivers simultaneously logging data during a session not including CORS This chart is not applicable to Levels 5 7 mapping grade surveys GPS User s Manual 6 19 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Monument Identification During the reconnaissance phase or in the course of the field survey a monument could easily be improperly identified This may result in the wrong monument being observed or the wrong identifier used in the field notes or digital data collection file This error can be controlled by requiring pencil rubbings or photos at the time reconnaissance is performed and during the course of the survey Each time a new or an existing station is observed a pencil rubbing or photo should be taken at the time of the observation for Level surveys For all other levels this practice is at the discretion of the party chief Data Collection Forms A sample GPS log sheets is shown in Figure 6 4 on the next page Please use this form or a similar one A way to link the form to the data file is important to the processing person In this case the form requests the GP
90. ion rather than the entirety of a control network redundant baselines Redundant baseline is a baseline observed to a point that has already been connected to the network by other observations A redundant baseline can be either an independent re observation of a previous measurement or an observation to a point from another base It is redundant because it provides more information than is necessary to uniquely determine a point Redundant observations are very useful They provide a check on the quality of previous measurements GPS User s Manual B 22 TxDOT 8 2005 Appendix B Glossary redundant Redundant is a repeated observation or an observation which contributes to over observation determining a network reference factor See standard error of unit weight reference frame A reference frame is the coordinate system of a datum reference station A reference station is a base station reference variance A reference variance is the square of the reference factor relative errors A relative errors are errors and precisions expressed for and between pairs of network adjusted control points relative precision The relative precision is defined as a measure of the tendency of a set of numbers to cluster about a number determined by the set e g the mean The usual measure is the standard deviation with respect to the mean Relative precision denotes the tendency for the various components X Y Z betwee
91. ion usually scheduled once a year with regular use is a reasonable interval for maintaining the accuracy of the instrument Instrumentation Requirements Summarized below are instrumentation and data collection requirements Table 4 1 Instrumentation Requirements Level of Survey Level 0 Level 1 Level 2 Level 3 Level 4 GPS Receivers Dual Frequency Required Required Required Recommended Recommended Single Frequency Not Not Not Acceptable Acceptable Acceptable Acceptable Acceptable GPS antennas Ground plane Ground Ground plane Ground plane Ground plane Required plane Required Optional Optional Required Tripods Fixed H I Fixed H I Fixed H I or Fixed H IL or Fixed H I or Required or Variable Variable Variable Variable 3d ant H I and centering 0 2 cm 0 2 cm 0 3 cm 0 4 cm 0 4 cm pos tolerance Minimum of GPS 3 3 2 2 2 receivers RTK acceptable No No No No Yes This chart does not apply to mapping level surveys Levels 5 6 and 7 Minimum of receivers simultaneously logging data during a session not including CORS Acceptable if points are located from more than one control point at different times GPS User s Manual 4 4 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 2 Instruments Personnel All field personnel should be trained in the avoidance of systematic errors during field operations Field personnel often work alone and must be
92. ion of one receiver relative to another When the data from these two receivers is combined the result is a baseline comprising a three dimensional vector between the two stations bench mark A bench mark is a relatively permanent object natural or artificial bearing a marked point whose elevation above or below an adopted datum is known Usually designated a BM such a mark is sometimes further qualified as a PBM permanent benchmark or as a TBM temporary benchmark CAF Combined Adjustment Factor CAF is the product of the scale factor and the elevation factor The CAF times the surface distance yields the corresponding distance on the State Plane grid Cartesian coordinates See Fixed Earth Centered Earth Cartesian coordinates chi square test Chi square is an overall statistical test of the network adjustment It is a test of the sum of the weight squares of the residuals the number of degrees of freedom and a critical probability of 95 percent or greater The purpose of this test is to reject or to accept the hypothesis that the predicted errors have been accurately estimated clock offset Clock offset is the constant difference in the time reading between two clocks In GPS usually refers to offset between SV clocks and the clock in the user s receiver closure Closure is an agreement between measured and known parts of a network coarse acquisition A course acquisition is a pseudorandom noise PRN
93. ional Procedures Identify and minimized all errors by redundancy analysis and careful operational procedures including the repetition of measurements under independent conditions make redundant ties to multiple high accuracy control stations ensure geodetic grade instrumentation field procedures and office procedures are used 4 ensure processing with the most accurate station coordinates satellite ephemerides and atmospheric and antenna models available Caution Be aware that these procedures cannot disclose all problems GPS User s Manual 2 4 TxDOT 8 2005 Chapter 2 Background Section 3 Surveying Vertical Networks with GPS Section 3 Surveying Vertical Networks with GPS Overview The use of GPS for vertical network surveys requires an understanding of the relationship between conventional and GPS height systems and problems unique to the vertical component of a GPS measurement Conventional trigonometric spirit or compensator leveling measures the relative elevations of points above an undulating equipotential surface called the geoid which is close to but not the same as mean sea level The model of this undulated geoid surface currently in use by TxDOT is GEOID03 TxDOT uses the NAVD88 vertical datum for orthometric height elevation measurements from this geoid surface GEOIDO3 and it has superceded the old NGVD datum of 1929 Elevations measured by conventional leveling are orthometric he
94. ios at the base station may transmit at full power but the TxDOT UHF transmitters are restricted to two watts The private sector does not have this 2 watt restriction on their itinerate frequencies The FCC radio license is for data transmissions This means TxDOT s radios have to stop transmitting when voice transmissions are being made Be sure the transmitter is equipped with a blocker Have the proper license and carry a copy with the equipment Rover Settings Configure equipment settings for the type of project to be surveyed It is a good idea to have all the possible options available while collecting data In many cases not every option is used However if needed they will be available Some options are to store raw observables at the base to allow for post processing of the base position should the need arise store vector information to allow the RTK data to be adjusted with least squares should the need arise set up the survey to allow for post processed kinematic data should the radio link be lost on a few shots Rover Initialization There are several ways to initialize a kinematic survey They can include a known baseline use of an initializer bar a new point and an on the fly OTF initialization After the first OTF initialization observe a point This can be a temporary mark or a point in the survey Discard the first OTF initialization and OTF re initialize with the H I changed by more than two feet o
95. lability the software will require a recent ephemeris file One internet site for obtaining this file is http www trimble com planningsoftware_ts asp Nav Collection 8425 Sky Visibility Prior to data collection the surveyor should look at each station to determine the extent if any of sky visibility obstructions greater than ten 10 degrees above the horizon This survey should include obstructions in all four 4 quadrants of the sky If there are obstructions the most desirable place for those obstructions to be located is northward of the station to be surveyed because of the design of the satellite constellation If there is an obstruction in that area it could still be a source of multipath at the GPS antenna Therefore the obstruction should be located Satellite Geometry The geometric quality of a constellation of satellites is measured by Position Dilution of Precision PDOP It is also measured by Geometric Dilution of Precision GDOP The difference between PDOP and GDOP is that GDOP considers time where PDOP only considers geometry The user should be aware of the manufacturer s recommendations of maximum DOP values for the various types of surveys the user will perform The vertical component of the GPS position is the most likely component to lack in quality if the DOP values are high Therefore if performing a vertical control survey collect data with conservative DOP values continued GPS User s
96. latitude amp longitude and vertically ellipsoid height within the specifications outlined by the manufacturer and with the local positional accuracy requirements for the level of survey being worked on GPS User s Manual 8 7 TxDOT 8 2005 Appendix A References Introduction These references are a listing of authors and works associated with the information found within this manual This appendix provides users with information for further reading Anderson Michael Don D Onofrio Gregory A Helmer and Wayne Wheeler 1995 Specifications for Geodetic Control Networks Using High Production GPS Surveying Techniques July Version 2 0 California Geodetic Control Committee Irvine CA Arkansas State Highway and Transportation Department 2004 Requirements and Procedures for Design Surveys and Land Surveys AHTD Surveys Division Berg Ronald 1998 Utilizing Real Time Kinematic GPS for Control Surveys Trimble User Conference Proceedings Ministry of Transportation Ontario Canada Bossler John D 1984 Standards and Specifications for Geodetic Control Networks Rockville MD September Federal Geodetic Control Committee National Geodetic Information Branch NOAA Doyle David 2000 State Plane Coordinates and The National Spatial Reference System March Texas Society of Professional Surveyors National Geodetic Survey Federal Geodetic Control Committee 1998 Geometric Geodetic Accuracy Standards and Specification for Us
97. m s project directory this must allow opening the project for review or continuation The following are reports from the processing adjustment program results of minimally constrained adjustment MCA results of final fully constrained adjustment must show held positions ASCII file of final coordinates in format name northing easting elevation feature code if used an ASCII file of ellipsoid heights for points with vertical determinations adjustment report showing network reference factor ratios of precision chi square test result etc e if topo data collected with RTK is included as a deliverable it should be in SDMS format and include figure numbers and or survey chains e TxDOT supported TGO software exports directly to the SDMS format There must be point connectivity break lines and the standard TxDOT feature codes must be used continued GPS User s Manual 8 4 TxDOT 8 2005 Chapter 8 Project Documentation and Deliverables to TxDOT Section 2 Project Documentation Digital Data continued e current list is the txdot2k feature code list The list along with figure number prompts that appear as attributes is available at district offices in Trimble format for Trimble TSC1 TSCe and ACU data collectors The file name is txdot2k fcl Other data collector firmware may export SDMS format Control Point Data Sheets A data sheet should be provided for individual Level 1
98. me is local solar mean time at Greenwich Meridian Some commonly used versions of Universal Time are UTO Universal Time as deduced directly from observations of stars and the fixed numerical relationship between Universal and Sidereal Time 3 minutes56 555 seconds UTI UTO corrected for polar motion UT2 UTI corrected for seasonal variation in the earth s rotation rate UTC Universal Time Coordinated uniform atomic time system kept very closely to UT 2 by offsets Maintained by the U S Naval Observatory GPS time is directly relatable to UTC UTC GPS 9 seconds in 1994 URA User Range Accuracy A URA is the contribution to the range measurement error from an individual error source apparent clock and ephemeris prediction accuracies which is converted to range units assuming that the error source is uncorrelated with all other error sources unknowns The computed adjustments to coordinates and transformation parameters also used to compute observation residuals US National Geodetic Survey This is the United States government agency that maintains the national geodetic datum and all geodetic survey control networks within the US and its territories US Survey Foot 1200 3937 meter The official unit of linear measure for NAD 27 UTC Universal Time Coordinated UTC is a time standard based on local solar mean time at the Greenwich meridian See also GPS time variance The square of the sta
99. mended Survey and Reduction Practices Intergovernmental Committee On Surveying amp Mapping 1996 Part D Documentation Practices amp Data Archiving Policy for a National Geodetic Data Base November Version 1 3 Publications Standards amp Practices for Control Surveys Recommended Survey and Reduction Practices Intergovernmental Committee On Surveying amp Mapping 1997 Use of the Global Positioning System GPS for Surveying Applications November Version 2 0 Publications Best Practice Guidelines GPS User s GuideManual A 2 TxDOT 8 2005 Appendix A References Natural Resources Canada Geodetic Survey Division 1996 Accuracy Standards for Positioning Version 1 0 Draft July Nevada Department of Transportation 2000 Special Instruction for Survey or Mapping Consultants April On Call Program Location Division Carson City NV NGS 1996 FBN Station Selection Guidelines May NGS 2000 Preliminary DRAFT Guidelines for Geodetic Network Surveys Using GPS May 15 NOAA 1997 Guidelines for Establishing GPS Derived Ellipsoid Heights November NOS NGS 58 NOAA Technical Memorandum North Carolina Department of Transportation 2000 Global Positioning System GPS Survey Guidelines North Carolina Department of Transportation Location and Surveys Manual Smith Curtis L July 1996 Revised NGS 3 Dimensional 3 D Rod Mark Draft Version National Geodetic Survey Sumpter Carl 1997 Standards and Specificati
100. n one station and other stations in the network to be clustered about the adjusted values Current custom is to express relative precision at the two standard deviation 95 confidence level This may be stated in terms of a relative error ellipse or as a proportion of the separation distance e g 10 ppm or 1 100 000 residual A residual is the correction or adjustment of an observation to achieve overall closure in a control network It is also any difference between an observed quantity and a computed value for that quantity RINEX Receiver INdependent EXchange format A RINEX is a standard GPS raw data file format used to exchange files from multiple receiver manufacturers RMS Root Mean Square A RMS expresses the accuracy of point measurement It is the radius of the error circle within which approximately 68 of position fixes are found It can be expressed in distance units or in wavelength cycles RMSE Root Mean Square Error rotated meridian A rotated meridian is a zone constant for the oblique Mercator mapping projection rotation In transformations a rotation is an angle through which a coordinate axis is moved around the coordinate system origin rover Rover is any mobile GPS receiver and field computer that is collecting data in the field The position of a roving receiver can be differentially corrected relative to a stationary base GPS receiver RTCM Radio Technical Commission f
101. n at intermediate positions Files containing these grids of geoidal separations are referred to as geoid models Given a WGS 84 position that falls within the extents of a geoid model the model can return the interpolated geoidal separation at this position geoid model A geoid model is a mathematical representation of the geoid for a specific area or for the whole earth The software uses the geoid model to generate geoid separations for the user s points in the network geoid separation Geoid separation is the distance between the ellipsoid and geoid at a given point geomatics Geomatics is the design collection storage analysis display and retrieval of spatial information The collection of spatial information can be from a variety of sources including GPS and terrestrial methods Geomatics integrates traditional surveying with new technology driven approaches making geomatics useful for a vast number of applications GPS Global Positioning System A GPS is based on a constellation of twenty four 24 satellites orbiting the earth at a very high altitude GPS baseline A GPS baseline is a three dimensional measurement between a pair of stations for which simultaneous GPS data has been collected and processed with differencing techniques Represented as delta X delta Y and delta Z or azimuth distance and delta height GPS observation A GPS observation is an uninterrupted collection of GPS data at a
102. n eastward reading of grid values Easting is read left to right on a grid X axis elevation Elevation is the height above mean sea level or the vertical distance above the geoid Elevation is sometimes referred to as the orthometric height elevation mask An elevation mask is an angle which is normally set from 10 20 degrees If a user tracks satellites from above this angle interference caused by buildings trees and multipath errors is avoided ellipsoid Ellipsoid is a mathematical model of the earth formed by rotating an ellipse around its minor axis For ellipsoids that model the earth the minor axis is the polar axis and the major axis is the equatorial axis Anellipsoid is defined by specifying the lengths of both axes or by specifying the length of the major axis and the flattening Two quantities define an ellipsoid these are usually given as the length of the semi major axis a and the flattening where b is the length of the semi minor axis ellipsoid distance An ellipsoid distance is the length of the normal section between two points Ellipsoid distance is not the same as the geodesic distance ellipsoid height An ellipsoid height is the distance measured along the normal from the surface of the ellipsoid to a point ephemeris An ephemeris is a set of data that describes the position of a celestial object as a function of time Each GPS satellite periodically transmits a broadcast ephemeri
103. n of the successful completion of the GPS survey project The printed technical report should include the following 4 4 4 o gt o make and model of the GPS receivers antennas and related equipment short narrative of the requirements of the survey listing of the control utilized and how the control compared against the field measurements statement that the survey met the standards and specifications set out in this document e statement should also include that the survey was performed under the direct supervision of the Texas Registered Professional Land Surveyor RPLS along with the surveyors registration number seal and date prepared chronological summary of all field operations software program generated report regarding the baseline processing results and the software and version number used software program generated report regarding the network adjustment results including a summary of covariance s standard deviation or values and the software and version number used network diagram map showing the network configuration as designed final observing schedule observation logs should be one log sheet per observation loop closure results results of Minimally Constrained Adjustment see Chapter 6 Minimally Constrained Adjustment for details of deliverables results of Fully Constrained Adjustment see Chapter 6 Fully Constrained Adjustment for details of deliverables photographs or pencil r
104. nalysis information Table 6 11 Office Procedures Guidelines Adjustment Analysis Criteria 1 cm Horizontal 2 cm Horizontal 2 cm Vertical 5 cm Vertical Maximum variance of unit weight 1 0 ideal 1 5 1 5 Minimum degrees of freedom per station 2 degrees of freedom 1 degree of freedom Standard deviation of observation residuals cm 01 cm 0 1 cm Standard error of baseline components cm 01 cm 0 1 cm Standardized residuals pass chi square test yes yes pass tau criterion yes yes Maximum observations rejected 10 10 Local Network Accuracy GPS User s Manual 6 45 TxDOT 8 2005 Chapter 7 Units Datum and Metadata Contents Section Over Wariiniai salita id 7 2 Section 2 Units and Da tii 7 3 section Mo e 7 5 GPS User s Manual 7 1 TxDOT 8 2005 Chapter 7 Units Datum and Metadata Section 1 Overview Section 1 Overview Purpose The purpose of this chapter is to provide the reader with specifications and guidelines covering essential GPS survey information GPS User s Manual 7 2 TxDOT 8 2005 Chapter 7 Units Datum and Metadata Section 2 Units and Datum Section 2 Units and Datum Units Unless otherwise instructed latitude and longitude will be presented as degrees minutes and seconds Direction indicators N or W will prefix the value and seconds will be carried out five places right of the decimal where accuracy is to approximately 001 feet The co
105. ndard error GPS User s Manual B 28 TxDOT 8 2005 Appendix B Glossary variance factor Reference variance variance of unit weight A statistical measure of how close the observation residuals match the predicted errors It is the square root of the sum of the weighted squares of the residuals divided by the degrees of freedom If the errors in a network have been weighted correctly the variance factor will approach 1 0 variance component A least squares technique for estimating the relative error estimation of different portions of a network variance group A variance group is one of the groups of observations for which variance component estimation is being used in a network adjustment variance covariance A variance covariance is the set of numbers expressing the variances and covariances matrix in a group of observations VDOP Vertical Dilution of Precision vector A vector is a three dimensional line between two points vertical A vertical is similar to the normal except that it is computed from the tangent plane to the geoid instead of the ellipsoid vertical adjustment A vertical adjustment is a network adjustment of vertical observations and coordinates only vertical control A Vertical control is an established benchmarks vertical control point A vertical control point is a point with vertical coordinate accuracy only The horizontal position is of a lower order of accuracy or is unk
106. ne combination The absolute value of the difference in each baseline component and the distance dependent error parts per million are analyzed to determine if blunders exist The difference in each vector component is compared to the rejection threshold RT The RT includes a base error and length dependent error that corresponds to the survey level In addition the results of the repeat baseline measurements should be compared to the instrument specifications stated by the manufacturer Equation for determining base errors RT pp SL pn d 10 12100 Where e Base error is 0 008m for survey level 0 amp 1 Base error is 0 01m for survey levels 2 4 SLppm Survey Level i e Level 0 4 d Distance in meters m b Similar to the repeat baseline closures known minus observed baseline closures provide insight on the location and possible cause of outliers The differences between the known vector and the observed vector components are compared to the same rejection threshold presented for repeat baseline closures c Computational loops should be composed of those baselines that close upon themselves in the shortest distance possible d Not required if survey method is PPK or RTK e In any component X Y Z the maximum misclosure in terms of loop length should not exceed this value in terms of parts per million ppm Take the misclosure divided the loop length times 1 000 000 to calculate each loop s ppm con
107. neral reference to the techniques used to estimate errors in a network adjustment survey observation A survey observation are the measurements made at or between control points using surveying equipment conventional or GPS SV satellite or space vehicle systematic errors Systematic errors are errors that occurs with the same sign They are often the same magnitude in a number of related observations target A target is any object to which the instrument is pointed A target may be a plumb bob or cord a nail in the top of a stake a taping arrow a range pole a pencil or any other object that will provide a sharply defined stationary point or line A target usually placed vertically over an unoccupied transit station tau value A tau is a value computed from an internal frequency distribution based upon the number of observations degrees of freedom and a given probability percentage 95 This value is used to determine if an observation is not fitting with the others in the adjustment If an observation s residual exceeds the tau it is flagged as an outlier Tau values are known as tau lines in the histogram of standardized residuals vertical lines left and right of the center vertical line tau criterion A tau criterion is Allen Pope s statistical technique for detecting observation outliers TDOP Time Dilution of Precision terrestrial observation A terrestrial observation is an observati
108. neth E and Donald J Huebner 1995 Error Accuracy and Precision The Geographer s Craft Project Department of Geography The University of Colorado at Boulder CO Gnipp Jack 1999 Vertical GPS Survey Standards 1999 Trimble User Conference Trimble Navigation Limited Gossett F 1950 rev 1959 Manual of Geodetic Triangulation Special Publication 247 U S Coast and Geodetic Survey Washington D C Greenfeld Joshua 2000 Survey Manual BDC99T 003 January New Jersey Department of Transportation Quality Management Services Configuration Management New Jersey Grontmij Geogroep bv MOVE3 User Manual Version 3 0 The Netherlands Hartzheim Paul and Darin Hendel 1998 Analysis of Real Time Kinematic and Fast Static Kinematic Least Squares Derived Coordinates Using a Wisconsin County UDN Trimble User Conference Proceedings Wisconsin Department of Transportation Hassler Richard 1999 Introduction to Network Adjustment 1999 Trimble User Conference Trimble Navigation Limited Sunnyvale CA Hothem Larry D 1988 Geometric Geodetic Accuracy Standards and Specifications for GPS Relative Positioning Techniques Version 5 0 May Federal Geodetic Control Committee Charting and Geodetic Services National Ocean Service NOAA Rockville MD Intergovernmental Committee On Surveying amp Mapping 1996 Network Adjustment Assessment November Version 1 3 Publications Standards and Practices for Control Surveys Recom
109. nown GPS User s Manual B 29 TxDOT 8 2005 Appendix B Glossary Ww WAAS Wide Area Augmentation System WASS is a satellite based system that broadcasts GPS correction information WAAS capable GPS receivers can track WAAS satellites WAAS is synonymous with the European Geostationary Navigation Overlay EGNOS and Japan s Multifunctional Transport Satellite Space based Augmentation System MSAS weight The weight is the inverse of the variance of an observation weights The set of weights or the inverse of the variance covariance matrix of correlated observations WGS 84 World Geodetic System 1984 WGS 84 is the mathematical ellipsoid used by GPS since January 1987 wide lane A wide lane is a linear combination of L1 and L2 carrier phase observations L1 L2 This is useful for its low effective wavelength 86 2 cm and for finding integer ambiguities on long baselines X Y and Z In the Earth Centered Cartesian system X refers to the direction of the coordinate axis running from the system origin to the Greenwich Meridian Y to the axis running from the origin through the 90x east longitude meridian and Z to the polar ice cap In rectangular coordinate systems X refers to the east west axis Y to the north south axis and Z to the height axis Y code Y code is an encrypted form of the information contained in the P code Satellites transmit Y code in place of P code when anti spoofing is in effect
110. ns for ionospheric free processing This is generally included in the processing software defaults and does not require user intervention GPS User s Manual 6 31 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Baseline Processing All baseline processing should be accomplished using NGS developed PAGES software or other interactive graphics producing software by other vendors that produces results equivalent to PAGES TxDOT surveyors can get help from the Information Systems Division ISD on Trimble TGO processing software Trimble s TGO software includes an adjustment program also supported by ISD See Table 6 6 for baseline processing requirements For sessions of an hour or more process data using 15 or 30 second epochs 5 second may be used but probably does not add anything to the accuracy and a 13 18 degree elevation mask outlined in Table 6 8 In no case will an elevation mask be applied that is greater than twenty 20 degrees above the horizon For sessions less than an hour static and faststatic observations may be processed using 5 or 15 second epochs However when operating FastStatic at the minimum observation time 8 to 20 minutes use 5 second data The use of shorter epochs may improve the ease of baseline processing Final processing should consist of fixing all integers for each baseline less than 40 kilometers For baselines less than 5 10 kilometers the L1 fixed solution may be t
111. ntical equipment is encouraged whenever possible GPS User s Manual 4 2 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 2 Instruments Section 2 Instruments GPS Receiver The receivers used for network surveys should record the full wavelength carrier phase and signal strength of both the L1 and L2 frequencies and track at least eight satellites simultaneously on parallel channels L1 only receivers are acceptable only for baselines less than 10 km Ties to CORS sites should be made with dual frequency instruments if base lines are longer than 10 km Receivers should have sufficient memory and battery power to record 6 hours of data at 5 second epochs Receivers should contain the latest manufacturer s firmware upgrades GPS Antenna The antennas should have stable phase centers and be designed to minimize multipath interference All antenna models used should undergo antenna calibration by the National Geodetic Survey NGS Users should consult user s manual for other specifications NGS Geodetic Services Division maintains a GPS Antenna Calibration Web site for calibrating a variety of antennas When processing GPS baselines the user must apply the appropriate GPS antenna phase center offsets Inappropriate phase center offsets can introduce up to 10 cm of error in the baseline GPS antenna ground planes should be utilized according to manufacturer specifications Ground planes must be utilized for all station
112. ntinued GPS User s Manual 3 7 TxDOT 8 2005 Chapter 3 Accuracy Standards TxDOT Standards continued Section 3 Local and Network Accuracy Table 3 5 TxDOT Local Accuracy Classification Level of Survey Accuracy Level 0 Level 1 Level 2 Level 3 Level 4 Local Accuracy Class 0 02 0 02 0 05 0 10 0 10 m Base Error m e 0 008 0 008 0 010 0 010 0 010 Ppm p 2 4 10 20 50 Minimum baseline 10000 3000 400 150 150 length m d Maximum baseline 20 000 10 000 10 000 5 000 3 000 length m d Maximum allowable 0 022 0 014 0 011 0 010 0 013 error based on minimum baseline length m s Maximum allowable 0 041 0 041 0 10 0 10 0 15 error based on maximum baseline length m s NGS Classification VI VI VII VII VII Range See Table 3 7 This table does not apply to mapping grade levels 5 6 and 7 Based on the level of survey accuracy listed in Table 3 4 Table 3 5 may be used as the standard for future classification of surveys performed for TxDOT The maximum allowable errors listed on the following page are based on All connected and unconnected baselines vectors within the minimally constrained and fully constrained network adjustments must comply with the 3 D relative positional error s required for the desired level of survey accuracy classification GPS User s Manual 3 8 continued TxDOT 8 2005 Chapter 3 Accuracy Standards Section 3 Local and Net
113. nts to determine baseline vectors and or unknown positions and performing adjustments and transformations to the processed vectors and positions Each step requires quality control analysis using statistical measures and professional judgment to achieve the desired level of confidence Each of these steps is also very dependent upon the measurement technique the GPS receiver and antenna types the observables recorded and the processing software The point position absolute coordinates of the initial station held fixed in each baseline solution must be referenced to the datum for the satellite orbits and must be known horizontally and vertically better than ten 10 meters Ideally all baselines should be processed with the initial published position of the CORS station or the highest accuracy station in the network From that initial coordinate NAD83 HARN latitude longitude and ellipsoid height all baselines should be processed seeding each of the new stations based on the results of the baseline processing from the known stations While technically WGS 84 is the datum of GPS the NAD83 datum may be accepted as an identical substitute for surveying in Texas Orbit Ephemeris Always use an ephemeris other than the broadcast or predicted ephemeris when processing The type of orbit ephemeris used can have an effect on the quality of processed baselines The longer the baseline the greater the effect can be For baselines exceeding
114. o the center of the earth define world geodetic datums Various datums have been established to suit particular regions For example European maps are often based on the European datum of 1950 ED 50 Maps of the United States are often based on the North American Datum of 1927 or 1983 NAD 27 NAD 83 All GPS coordinates are based on the WGS 84 datum surface geographic geodetic coordinates Latitude longitude and ellipsoid height GPS User s Manual B 9 TxDOT 8 2005 Appendix B Glossary geoid A geoid is the surface of gravitational equipotential that closely approximates mean sea level It is not a uniform mathematical shape but is an irregular figure Generally the elevations of points are measured with reference to the geoid However points fixed by GPS methods have heights established in the WGS 84 datum a mathematical figure The relationship between the WGS 84 datum and the geoid must be determined by observation as there is no single mathematical definition that can describe the relationship The user must utilize conventional survey methods to observe the elevation above the geoid and then compare the results with the height above the WGS 84 ellipsoid at the same point By gathering a large number of observations of the separation between the geoid and the WGS 84 datum geoidal separation grid files of the separation values can be established This allows the interpolation of the geoidal separatio
115. ocessing software to allow one to examine the observational information to detect obvious problems continued GPS User s Manual 6 32 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Troubleshooting Problematic Baselines continued The following are suggestions on what to look for when troubleshooting problematic baselines Look at the plot of all satellites during the observing session there is a plot for each receiver Software packages differ but common to most is a plot showing each satellite observed one below the other What to look for e When a cycle slip occurs or there is a loss of lock due to obstructions there will be a break in the line on the graph for that particular satellite e A short break indicates a cycle slip a longer break an obstruction e If too many breaks have occurred eliminate that satellite and try the baseline solution again In many cases this solves the problem Look at the plot of satellites for both receivers e Was the start and stop time approximately the same or did one receiver start or stop too early or too late e Start and stop times can be changed to encompass only common observing times and then re observe the baseline Satellites with a high signal to noise ratio SNR can cause problems In many cases a high SNR occurs when the satellite is close to the horizon It is possible to have a satellite low on the horizon for the en
116. odetic horizon are expressed as North East and Up The LGH is used for rotating EC Cartesian Coordinate differences before modeling a baseline on the ellipsoid Azimuth values computed from LGH components must be corrected for skew normals as part of modeling on the ellipsoid loop closure Loop closures provide an indication as to the amount of error in a set of observations within a network A loop closure is calculated by selecting a point from which one or more observations were taken adding one of those observations to the point s coordinates and calculating coordinates of the second point based on that observation This process is repeated one or more times around a loop finally ending at the original starting point If there were no errors in the observations the final calculated coordinate would be exactly the same as the original starting coordinate By subtracting the calculated coordinate from the original coordinate a misclosure is determined Dividing this error by the length of the line allows the error to be expressed in parts per million This technique can also be used between two different points when both points are known with a high degree of accuracy This is also known as a traverse closure GPS User s Manual B 15 TxDOT 8 2005 Appendix B Glossary M major axis See ellipsoid mapping angle Mapping angle is the angle between grid north on a mapping projection and the meridian of longitude
117. of receivers operating inner constraint An inner constraint is a network adjustment computed without fixing any point coordinates integer ambiguity Integer ambiguity is the whole number of cycles in a carrier phase pseudorange between the GPS satellite and the GPS receiver integer search Integer search is the GPS baseline processing whether real time or postprocessed requires fixed integer solutions for the best possible results The software which processes the GPS measurements used to derive a baseline does an integer search to obtain a fixed integer solution The search involves trying various combinations of integer values and selecting the best results iono free lonospheric free solution lonoFree lonoFree is a solution that uses a combination of GPS measurements to model and remove the effects of the ionosphere on the GPS signals This solution is often used for high order control surveying particularly when observing long baselines ionosphere The ionosphere is part of the atmosphere 80 to 120 miles above the earth s surface It affects the accuracy of GPS measurements if the user measures long baselines using single frequency receivers ionosperic delay An ionopheric delay is a signal delay or acceleration as a wave propagates through the ionosphere Phase delay depends upon the electron content and affects the carrier signal Group delay depends upon the dispersion in the ionosphere as well and aff
118. on in the field using a laser rangefinder or conventional instrument GPS User s Manual B 26 TxDOT 8 2005 Appendix B Glossary tie A tie is a survey connection from a point of known position to a point whose position is desired total station A total station is an electronic theodolite that provides both angle and distance measurements and displays them automatically TOW Time of Week TOW is measured in seconds from midnight Saturday night Sunday morning GPS time tracking The process of receiving and recognizing signals from a satellite transformation A transformation is the rotation shift and scaling of a network to move it from one coordinate system to another transformation group A transformation group is a selected group of observations used to compute transformation parameters unique to that group of observations Typically the observations within the group are the same type with similar errors and measured using a common method transformation parameters Transformation parameters is a set of parameters derived for a network adjustment or user parameters defined that transform one datum to another Typically with GPS the parameters are generated to transform WGS 84 to the local datum transit station A mark over which the instrument is has been or will be accurately positioned for use tribrach A tribrach is a centering device used for mounting GPS antennas and other survey instrum
119. ons for Global Positioning System GPS Surveys Cadastral Surveys October Version 1 4 USDA Forest Service Rocky Mountain Region Northern Boundary Management Zone Laramie Wyoming Sumpter Carl Mike Londe Ken Chamberlain and Ken Bays 2000 Standards and Guidelines for Cadastral Surveys using Global Positioning System Methods United States Department of Agriculture Forest Service United States Department of the Interior Bureau of Land Management Texas Department of Transportation 1994 Standards and Specifications for Global Positioning System GPS Surveys in Support of Transportation Improvement Projects December Draft Survey Department San Antonio TX Trimble Navigation Limited 1999 Trimble Geomatics Office Network Adjustment Software User Guide November PN39933 00 ENG Version 1 0 1999 Trimble Navigation Limited Sunnyvale CA US Army Corps of Engineers 1991 Navstar Global Positioning System Surveying EM 1110 1 1003 June Engineering and Design Department of the Army Washington DC US Army Corps of Engineers 1994 Deformation Monitoring and Control Surveying October EM 1110 1 1004 Engineering and Design Department of the Army Washington DC US Army Corps of Engineers 1998 Using Differential GPS Positioning For Elevation Determination ETL1110 183 April Engineering and Design Department of the Army Washington DC GPS User s GuideManual A 3 TxDOT 8 2005 Appendix A References U S Bureau o
120. ontinued CONTROL MONUMENTATION F G U SPOTS BREAKS AS BUILT Aerial Target F Azimuth Mark Existing F Azimuth Mark New F Bench Mark Azimuth F Brass Cap F Benchmark New F Benchmark Magnetic F Box Panel Flight F Benchmark Reference F Benchmark Temporary F Benchmark Traverse F Benchmark Triangulation F Chiseled Drilled or Plug Mark F Chiseled Plus SCRIBE F Concrete Marker Cast Type F Construction Point Temp F County Line F F Control Point F Country Line F F Center Sec Corner F Disk Mon Rod with Cap Type III F GPS Monument Add Number as Pd F Horizontal Pane F Hour Glass Panel F NGS Marker Horizontal Only F Flight Panet Vertical Only F Hub tack F NGS Marker Horizontal amp Vertical F Iron Bar Also see JR F Iron Pipe Also see 1B F Iron Rod F Lot Corner F Concrete Monument Poured Type 11 F Nail 60d Conc W Shiner F NGS Marker Horizontal Only F Nail and Shiner F Parcel F F Parcel Remainder F F Parcel Take F F Property Corner G PK Naif F Subdivision Block Lot Prop Line F F Plat Corner F Principal Point F Ring amp Bolt F Reinforcement Bar F Reference Marker F Right of Way Proposed F F Right of Way Existing G F Rail Road Spike
121. or Maritime Services RTCM is a commission established to define a differential data link for the real time differential correction of roving GPS receivers GPS User s Manual B 23 TxDOT 8 2005 Appendix B Glossary RTK A real time kinematic is a type of GPS survey SAF Surface Adjustment Factor SAF is a published TxDOT developed value for each county which when multiplied times a distance on the State Plane grid yields the corresponding distance on the surface satellite geometry A satellite geometry is a position and movement of GPS satellites during a GPS survey scalar In least squares a scalar is a value applied to the variances errors based on the required level of confidence scale A scale is a multiplier used on coordinate and other linear variables such as for map projections and transformations SDMS Survey Data Management System SDMS is a data collection software and data processing software maintained by AASHTO secular motion A secular motion is that portion of crustal motion which is continuous and at a constant velocity Secular motion is uniformly predictable over time and is independent of any seismic events selective availability S A SA is an artificial degradation of the GPS satellite signal by the U S Department of Defense The error in position caused by S A can be up to 100 meters semimajor axis Semimajor is one half of the major axis semiminor axis Semimin
122. or as a result of a complete loss of lock on the satellites the previous station surveyed must be surveyed a second time with a new initialization Level 5 Surveys Level 5 surveys include mapping grade work that is held to sub meter network accuracy Examples of this type of work include locative and inventory data gathering for a GIS system Equipment used will generally be code based GPS receivers enabled to receive real time corrections from base station positions In many cases Coast Guard beacons OmniStar Racal and other third party providers of differential corrections will provide the necessary component for spatial data for other than design and construction use If the situation warrants data can also be post processed Level 6 Surveys Level 6 surveys include mapping grade work that may not be sub meter but is at least within five meters network accuracy Examples of this type of work include locative and inventory data gathering for a GIS system where positional information is not as critical as for a Level 5 survey Equipment used will generally be code based GPS receivers enabled to receive real time corrections from base station positions but at farther distances from the base or with less stringent parameters GPS User s Manual 6 18 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Level 7 Surveys Level 7 work includes very rough positioning with an autonom
123. or is one half of the minor axis session A session is a period during which a number of GPS receivers log satellite data simultaneously for the purpose of creating baselines set up error Set up errors are errors in tribrach centering or height of instrument at a control point sideshot A sideshot is an observed baseline with no redundancy sigma Sigma is a mathematical symbol or term for standard error single frequency Single frequency is a type of receiver that only uses the L1 GPS signal There is no compensation for ionospheric effects GPS User s Manual B 24 TxDOT 8 2005 Appendix B Glossary site calibration Site calibration is a process of computing parameters which establishing the relationship between WGS 84 positions latitude longitude and ellipsoid height determined by GPS observations and local known coordinates defined by a map projection and elevations above mean sea level The parameters are used to generate local grid coordinates from WGS 84 and vice versa real time in the field when using RTK surveying methods skyplot A skyplot is a polar plot that shows the paths of visible satellites for the time interval selected for the graph The elevation of the satellite is represented in the radial dimension and the azimuth is shown in the angular dimension The result depicts the satellite s path as it appears to an observer looking down from a place directly above the survey point solution
124. ordinate system used by TxDOT is the State Plane Coordinate System in NAD83 however units of length will be in U S Survey Feet rather than meters Horizontal coordinates should be carried out to 001 ft unless otherwise instructed Processing and adjusting GPS data may be done in the metric system but all project data must be delivered in U S Survey Feet Conversion from meters to U S Survey Feet must be made using the following formula Meters 3937 1200 U S Survey Feet The factor is 3 280833333333 and working with SPC s in the millions one must carry the factor out to 12 places to the right of the decimal as shown Datum All geodetic surveying with GPS will be done in the NAD83 horizontal datum An adjustment was done in Texas using GPS which resulted in the 1993 HARN network The network was extended to nearly all old conventionally surveyed federal monumentation Projects should be referenced to the published HARN coordinates of NGS monumentation Elevations will be referenced to the NAVD88 vertical datum Surface Coordinates vs State Plane Grid Coordinates Depending on how far north or south the project falls in the state plane zone and depending on the elevation of the area GPS coordinates in the State Plane Coordinate System most likely will need to be adjusted so that lengths measured on the surface will coincide with lengths inversed on the surface projection state plane grid An exception to this is when RTK w
125. ork is done after calibrating the equipment to control in already existing surface coordinates continued GPS User s Manual 7 3 TxDOT 8 2005 Chapter 7 Units Datum and Metadata Section 2 Units and Datum Surface Coordinates vs State Plane Grid Coordinates continued The TxDOT surveyor or engineer for the project may calculate a combined adjustment factor CAF to be used on the project The surveyor or engineer also might dictate that a standard county wide TxDOT Surface Adjustment Factor SAF be used or may ask a consultant to calculate their own It is not important what method is used to arrive at the factor but it is absolutely necessary that the factor used is included in the metadata notes Highway projects with several CAF s pose no problem when all coordinates can be backed down to SPC s so everything will match The juncture of two systems however needs to be well identified so that all measurements stop or begin at a common point Stationing must not cross this line without a station equation Cut and fill volumes can t be calculated across the line Only State Plane Coordinates can be used seamlessly If coordinates have been truncated for easier calculations or for identification they must be returned to their full configuration before delivery This is not only for standardization it is so that the coordinates will work in the seed files for microstation as well GPS User s Manual 7 4 TxDOT 8 2005 Cha
126. ous fix usually using a handheld consumer type GPS receiver Positions will generally be good to within thirty 30 meters Raw GPS data cannot be stored and retrieved for post processing as with equipment used in all other TxDOT levels of surveys Field Quality Control There are several areas to be addressed as far as quality control for the field data acquisition GPS surveys Quality control measures ensure that the field measurements are performed correctly There are three 3 sources for error in any survey whether it is a GPS survey or a conventional survey These sources for error are blunders systematic errors and random errors The goal of quality control is to eliminate the blunders and the systematic errors Then all that is left are random errors With a good network design and a sufficient number of redundant measurements the random errors can be handled and minimized to yield the best possible final result The following table identifies field data collection information Table 6 2 Field Data Acquisition Requirements Level of Survey Accuracy Level 0 Level 1 Level 2 Level 3 Level 4 Minimum Elevation Mask in Degrees Collection 10 13 13 10 13 Acceptable Survey Method S S S R F S R F R F PPK PPK RTK RTK Maximum DOP Value M M M M M If adj Tripod then Minimum Number H I Measurements 6 6 6 6 6 Maximum H I Height Difference Between Measurements 3mm 3mm 4mm 4mm 5mm M
127. pe Yellow Dashed G G Paint Stripe Yellow Solid G G Signa Control Panel F Sign and Pole Single F Signal Pedestal F Signal Span Wire Support Mast Arm A Traffic Signal Light Pole Single F Traffic Separator G F VEGETATION TREES LANDSCAPING DRIP Tree Drip Lines G F ISP Irrigation Stand Pipe G HDG Hedge G F GPS User s Manual Omamental Plant G Orchard Grove G F Orchard Trees G Coniferous Tree G Planter G F Shrub G Tree Stump F Tree Farm Outline G F Tree G Tree Larger Than TR G Tree Larger Than TRE G Tree Larger Than TREE G Edge of Trees Woods G F UTILITIES ELECTRIC TELEPHONE amp CABLE Conduit Electric G F Conduit Telephone G F Cable TV Pedestal F Cable TV Service Box F Cable TV Line G F Electric Meter F Encasement Pipe F F Electrical Pedestal F Easement Lines G F Fiber Optic Cable G F Guy Pole Deadman G Guy Anchor G High Voitage Transmission Line G F Transmission Line Tower Leg G Invert Electric Flow Line ZONE 3 P Invert Telephone Flow Line ZONE 3 F Junction Box Electric G Junction Box Telephone G Luminare Standard F Manhole Electric G Manhole Telephone G Power Line Overhead Elec G F Telephone Line Overhead G F Pull Box F Power Pole G Power Pedestal F Service Pole Electric G Service Pole Telephone G Telephone
128. pied a minimum of two 2 times baselines should have a fixed integer double difference solution or adhere to the manufacturer s specifications for baseline lengths exceeding the fixed solution criteria i e float solution may be the best solution for baselines in excess of 100 km depending on manufacturer specifications and recommendations any station pair used as azimuth or bearing reference for use with conventional survey measurements during the course of any other survey level should be included in a network or measured as a radial line with a minimum of two 2 independent baselines the district network must be a geometrically closed figure therefore single radial spur lines or side shots to points are not acceptable Radial lines are acceptable only for setting azimuth marks Level 2 Surveys This level includes primary project control and control for airborne aerial photography or LiDAR data gathering These points in the project area are tied to the NSRS through Level 1 control points and or CORS and FBN CBN points if they fall within about sixty 60 miles of the project A primary project control network usually is established by the static survey method The primary project control network may be established at the same time the other survey Levels are being performed However the points and resulting baseline vectors used in the primary project control network should be processed to derive the baseline solutions and
129. pter 7 Units Datum and Metadata Section 3 Metadata Section 3 Metadata Identifying Delivered Coordinates All coordinates files or lists delivered whether hardcopy or in digital medium must contain metadata indicating the CAF or SAP horizontal datum and adjustment vertical datum geoid model if applicable units of measure and the date of the field work This would include hard copy drawings CAD drawings the data sheets and each sheet containing coordinates in a report and ASCII or LandXML files See Chapter 8 Section 2 regarding individual data sheets for new control points Conversions and Transformations Where design survey accuracy is required TxDOT will not accept any datum transformations There is no way to accurately transfer NAD27 coordinates to NAD83 datum CORPSCON and other conversion software programs are based on NADCON algorithms which perform a rubber sheeting adjustment that is not accurate If a change to the NAD83 project datum is needed for comparison of old surveys two 2 control points can be resurveyed GPS or conventional from references in the new datum Then a translation rotation scale can be done holding to the two 2 points common to both datum Or if original raw GPS data is available it can be reprocessed holding the new datum coordinates rather than the original datum coordinates Both CORPSCON and AASHTOW are SDMS Processor are acceptable software programs for the mathematical con
130. r ambiguity search with enough confidence to select one set of integers over another It is called a float solution because the ambiguity includes a fractional part and is non integer free adjustment Performs a network adjustment in which no point coordinate is constrained The network adjustment uses inner constraints frequency Frequency is the size and spread of residuals in a data set graphically shown in distribution histograms fully constrained Fully constrained is a network adjustment in which all points in the network that are part of a larger control network are held fixed to their published coordinate values Fully constrained is used to merge smaller with larger control networks and old to newer networks GDOP Geometric Dilution of Precision GDOP is the relationship between errors in user position and time and errors in satellite range See also DOP geodetic azimuth A geodetic azimuth is the angle between the geodetic meridian and the tangent to the geodesic line of the observer measured in the plane perpendicular to the ellipsoid normal of the observer clockwise from north geodetic datum A geodetic datum is a mathematical model designed to fit part or all of the geoid It is defined by the relationship between an ellipsoid and a point on the topographic surface established as the origin of a datum The size and shape of an ellipsoid and the location of the center of the ellipsoid with respect t
131. r greater GPS User s Manual 6 10 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 4 Monumentation Section 4 Monumentation Overview The knowledge of important considerations which ensure the stability and continued usability of monuments is vital to successful monumentation The references to procedures and guidelines presented within this section aid the user in properly establishing a GPS survey monument Monumentation Guidelines For monumentation guidelines refer to Appendix A of this manual or the National Geodetic Web site at http www ngs noaa gov GPS User s Manual 6 1 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 5 Survey Methods Section 5 Survey Methods Static Positioning Static positioning typically uses a network or a multiple baseline approach for positioning It may consist of multiple receivers multiple baselines multiple observational redundancies and multiple sessions After processing the data to obtain baselines a least squares adjustment of the results is required This method provides the highest accuracy achievable and requires the longest observation times from an hour to five hours or longer Static positioning is primarily used for ties to the NSRS when observing for TxDOT Level 1 and 2 surveys However this technique could be used for the other levels listed in Chapter 3 Table 3 4 of this manual using project control points FastStatic Rapid Static
132. r move more than forty feet away from the point to be used as a check After the new OTF initialization has been accomplished return to the point being used as a check and re shoot it Compare the first and second shots Are they within an acceptable tolerance continued GPS User s Manual 6 24 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Rover Initialization continued If the points check proceed with data collection with the confidence in surveying with a correct initialization If the error between the two points is beyond the expected error one or both of the OTF initializations used for a check are incorrect OTF re initializations at any of the positions previously used cannot be reused The location must change by a difference of more than two feet of H I or more likely move more than forty feet away in a different direction This will usually provide enough information to identify the OTF initialization that is incorrect Once the problem is solved begin the survey This procedure must be repeated with any loss of initialization Each time a re initialization is done as a result of a complete loss of lock on satellites the first station surveyed thereafter must be surveyed a second time with a new initialization from which the survey can continue if the two initializations agree continued GPS User s Manual 6 25 TxDOT 8 2005 Rover Initialization c
133. r printed copies changes updates and edits However paper copies may be used in the field Copies should be checked for currency date Caution should be taken not to rely on the printed version due to ongoing updates and or changes The information within this manual is governed by the laws and standards of information security Please refer to the Information Security Manual for specific security information Documentation of Authority The following documents authorize the TxDOT GPS User s Manual and the activities it covers TxDOT Directive 5 92 TxDOT Manual System Executive Order 1 89 Policy and Procedures Communication TxDOT Policy Statement 2 96 Information Security Laws and Standards The GPS User s Manual provides the information that TxDOT GPS and survey resource users need to comply with applicable legal and policy requirements Based on federal and state laws state standards and agency policy this manual draws upon the following Texas Government Code Section 2203 004 Requirement to Use State Property for State Purposes Texas Government Code Section 403 275 Liability for Property Loss GPS User s Manual 1 2 TxDOT 8 2005 Chapter 1 Introduction Section 1 Overview Purpose of the TxDOT GPS User s Manual This manual is intended for use by TxDOT surveyors as well as consultants This manual was developed to provide TxDOT employees and contractors with the concepts policies standards proc
134. rger pseudorange estimate and increases the error Multiple paths may arise from reflections from structures near the antenna GPS User s Manual B 16 TxDOT 8 2005 Appendix B Glossary N NAD27 North American Datum of 1927 NAD83 North American Datum of 1983 narrow lane A narrow lane is a linear combination of L1 and L2 carrier phase observations L1 L2 that is useful for canceling out ionospheric effects in collected baseline data The effective wavelength of the narrow lane is 10 7 centimeter NAVD88 North American Vertical Datum of 1988 NAVDATA NAVDATA is the 1500 bit navigation message broadcast by each satellite This message contains system time clock correction parameters ionospheric delay model parameters and details of the satellite s ephemeris and health The information is used to process GPS signals to obtain user position and velocity network A network is a set of baselines See also subnetwork network adjustment A network adjustment is a solution of simultaneous equations designed to achieve closure in a survey network by minimizing the sum of the weighted squares of the residuals of the observations network status Network status is an indication that a particular observation will be included in the adjustment Network means that it is included in the adjustment and non network means that it is excluded from the adjustment NGVD29 National Geodetic Vertical Datum of 1929
135. rically closed figure therefore single radial spur lines or side shots to points are not acceptable e radial lines are only acceptable and required for station pairs where one of the stations will be primarily used as an azimuth mark all stations tied with RTK should be measured twice with a new initialization in between the two ties e atthe minimum time difference specified in Chapter 5 Table 5 1 a second set of measurements should be taken e this will yield a total of four sets of independent observations two pair at each point e in most cases each pair will be measured from different base station locations GPS User s Manual 6 17 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Level 4 Surveys Level 4 survey work includes wing panels for horizontal position only see Chapter 3 Table 3 4 side shots for topographical survey and stake out Survey methods used can be RTK or fast rapid static observations from higher level points All Level 4 points should conform to the requirements outlined in Tables 4 1 5 1 6 2 6 6 and 6 8 of this manual to include the following requirements Be referenced to one or more TxDOT Level 1 2 or 3 stations NSRS FBN or CBN published horizontal control stations Atleast 10 of the Level 4 points should be checked with a second observation after a new initialization Each time an initialization is done for the first time
136. roduced PRN codes have a low autocorrelation value for all delays or lags except when they are exactly coincident 2 Each NAVSTAR satellite can be identified by its unique C A and P pseudorandom noise codes so the term PRN is sometimes used as another name for GPS satellite or SV probability Probability is a statistical percentage expressing what portion of a hypothetical number of observations will fall within the defined limits It is sometimes called level of significance probable value A probable value is the adjusted value for observations and other quantities assuming that the adjustment has been done correctly It is the closest approximation to true value that is possible projection A projection is used to create flat maps that represent the surface of the earth or parts of the Earth s surface propagated error The propagated errors are computed errors derived from estimated observational errors and expressed in terms of coordinate positions Propagated coordinate errors may in turn be propagated into relative errors in azimuth distance and delta height between points pseudorange A pseudorange is a measure of the apparent propagation time from the satellite to the receiver antenna expressed as a distance The apparent propagation time is determined from the time shift required to align a replica of the GPS code generated in the receiver with the received PGS code The time shift is the difference b
137. rtant part of the performance of a control survey utilizing GPS survey measurement techniques Proper planning will give one added confidence that quality data will be collected Regardless of the level of the survey the items listed below should be addressed before the field data collection process begins Reconnaissance Prior to the commencement of any TxDOT survey all significant aspects of the project should be understood so that the project can be performed effectively and efficiently Based on the TxDOT level of survey to be performed go to Chapter 4 Table 4 1 and Chapter 5 Table 5 1 and review the specifications for the project Perform a reconnaissance survey of the site to determine the location and sky visibility of existing and new control stations pick the locations for new stations making sure satellites can be recorded in a minimum of three quadrants look at logistics of project and determine transportation required gain permission to access station s on private land if applicable the surveyor should notify law enforcement of their activities record sky visibility chart data and access requirements for all stations look for any objects that could be sources for radio interference look for any multipath conditions that may affect data collection GPS User s Manual 6 4 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 3 Planning Monumentation for New Stations All monumentation for new
138. s at the beginning of the observing session and again at the end of the observing session The H I must be recorded in a field book or on log sheets for every occupation Static Observation Field Procedures All control stations and boundary corners should be occupied a minimum of two times during the course of a survey Table 5 1 in Chapter 5 outlines how those occupations should be accomplished The normal collection rate epoch is 5 seconds for static observations but for long observation times of more than about 3 hours 15 second epochs are acceptable For observations of less than half an hour 5 second epochs are preferable For fast rapid static observations 5 seconds is required RTK is done at 1 second Longer baselines will require longer observations on end points Minimum observation times for Levels 2 and 3 are listed in Table 6 3 Allowances should be made for difficult setups that may have less satellite visibility or high PDOP Level 1 surveys usually involve long distances and will almost always require observation times of 4 to 6 hours and at least two occupations The following table illustrates minimum observation times Table 6 3 Minimum Observation Times for Surveys Levels 2 and 3 Length of Baseline Minimum observation time less than 10 km 45 min 10 to 40 km 1 hr 40 to 100 km 2 hr 100 to 200 km 3 hr more than 200 km 4 hr or more Assuming at least 5 satellites and P
139. s describing its predicted positions through the near future uploaded by the control segment Postprocessing programs can also use an ultra rapid rapid or precise ephemeris which describes the exact positions of a satellite in the past epoch An epoch is the measurement interval of a GPS receiver The epoch varies according to the survey type epoch date The epoch date is the date usually expressed in decimal years for which published coordinates and data are valid epoch interval Epoch interval is the measurement interval used by a GPS receiver also called a cycle error An error is the difference between the measured value of a quantity and its true value Surveying errors are generally divided into three categories blunders systematic errors and random errors Least squares analysis is used to detect and eliminate blunders and systematic errors and least squares adjustment is used to measure and properly distribute random error error ellipse An error ellipse is a coordinate error ellipse is a graphical representation of the magnitude and direction of the error of network adjusted points GPS User s Manual B 7 TxDOT 8 2005 Appendix B Glossary events Events are represented as a record of the occurrence of an event such as the closing of a photogrammetric camera s shutter A GPS receiver can log an event mark containing the time of the event and an alphanumeric comment entered through the keypad to de
140. s has been described by a proportional standard e g 1 10 000 which reflected the distance dependant nature of terrestrial surveying error The accuracy of GPS surveys being less distance dependant requires different accuracy standards Federal Geographic Data Committee Methodology The use of multiple standards creates difficulty in comparing the accuracy of coordinate values obtained by different survey methods In recognition of these difficulties the Federal Geographic Data Committee FGDC has changed its methodology for reporting the accuracy of horizontal and vertical coordinate values Defining the new reporting standard is the two sigma 20 confidence intervals a circle for horizontal uncertainty and a linear value for vertical uncertainty Figure 3 1 3 D Accuracy GPS User s Manual 3 3 TxDOT 8 2005 Chapter 3 Accuracy Standards Section 3 Local and Network Accuracy Section 3 Local and Network Accuracy Standards The new standards support both local and network accuracies The local accuracy of a control point is a value that represents the uncertainty in the coordinates of the control point relative to the coordinates of other directly connected adjacent control points at the 95 percent 20 confidence level e The reported local accuracy is an approximate average of the individual local accuracy values between a control point and other observed control points used to establish the coordinates of the con
141. s lock onto a satellite s radio signals A cycle slip requires the re estimation of integer ambiguity terms during baseline processing data collector A data collector is a handheld electronic field notebook It connects to a total station level or GPS receiver to receive and temporarily store raw data data logging Data logging is the process of recording satellite data in a file stored in the receiver a data collector or on a PC card data message A data message is a message included in the GPS signal that reports on the location and health of the satellites as well as any clock correction It includes information about the health of other satellites as well as their approximate position datum Datum is a mathematical model of the earth designed to fit part or all of the geoid It is defined by the relationship between an ellipsoid and a point on the topographic surface established as the origin of the datum It is usually referred to as a geodetic datum The size and shape of an ellipsoid and the location of the center of the ellipsoid with respect to the center of the earth usually define world geodetic datums datum transformation Datum transformation defines the transformation that is used to transform the coordinates of a point defined in one datum to coordinates in a different datum There are a number of different datum transformation methods seven parameter three parameter also referred to as Molod
142. s when performing TxDOT Level 1 and Level 2 surveys For other surveys a ground plane must be used at the base station and should be utilized in areas where there might be significant multipath Many new antenna models have built in ground planes GPS RTK Rover Rod A fixed height rover rod should be used and if possible it should be the same height as any fixed height tripods on the project usually 2 meters Make a physical measurement in the field notes to verify it has been checked Also check the level bubble on the rod before and after each project GPS User s Manual 4 3 TxDOT 8 2005 Chapter 4 Equipment and Resources Section 2 Instruments Tripods The tripods must facilitate precise offset measurements between the mark datum point and the antenna reference point ARP Fixed height rods or fixed height tripods are preferable and required for certain surveys due to the decreased potential for antenna centering and height measurement errors All tripods should be examined for stability with each use Ensure that hinges clamps and feet are secure and in good repair Test the fixed height tripods for stability plumb alignment and height verification at the start and end of each project Tribrachs Tribrachs and rod levels should be field calibrated before use on each project and should be checked at the end of the project Any data not bracketed by a successful calibration check are suspect Professional Tribrach calibrat
143. scribe the event An event can be triggered through the keypad or by an electrical signal input on one of the receivers ports fast ambiguity resolution Fast ambiguity resolution is rapid static or fast static GPS surveying techniques utilizing multiple observables dual frequency carrier phase C A and P codes to resolve integer ambiguities with shortened observation periods The method may also be used for observations with the receiver in motion known as on the fly ambiguity resolution FastStatic FastStatic is a method of GPS surveying using occupations of up to 20 minutes to collect GPS raw data then postprocessing to achieve sub centimeter precisions Typically the occupation times vary based on the number of satellites SVs in view FastStatic is also referred to as RapidStatic FBN Federal Base Network An FBN consists of A and B order stations set by the NGS for the purpose of densifying the National Spatial Reference System FCA An FCA is a fully constrained adjustment feature codes Feature codes are abbreviations used to define an object collected during a radial survey FGDC A Federal Geodetic Data Committee fixed See constrained fixed earth centered earth An earth centered is a Cartesian coordinate system used by the WGS 84 reference frame In this coordinate system fixed refers to the center of the system that is at the earth s center of mass The z axis is coincident with the me
144. sources Chapter 4 presents information regarding the use of GPS instruments and equipment It includes discussions on the requirements for accurate and consistent data collection for a variety of instruments and equipment This chapter also provides information on Internet resources Chapter 5 Network Design Chapter 5 discusses network design and includes the determination of the number and location of existing control stations for network constraints as well as selection of new project control stations and relative dispersion of network observations GPS User s Manual 1 4 TxDOT 8 2005 Chapter 1 Introduction Section 2 Chapter Descriptions Chapter 6 GPS Survey Specifications Chapter 6 covers specifications involved in the planning of a project field data acquisition methods field survey operations and procedures data processing analysis of the data and documentation This chapter also provides information on monumentation survey methods field survey operations and procedures and data processing Chapter 7 Units Data and Metadata Chapter 7 provides information regarding the units used in TxDOT work horizontal and vertical datum adjustment factors requirements for delivering metadata lists and files and provisions for conversions and transformations Chapter 8 Project Documentation and Deliverables to TxDOT Chapter 8 TxDOT requirements for project documentation and deliverables are outlined in this chapter Sp
145. summarizes all of the requirements for baseline vector analysis Baseline Processing Reports The user should pay close attention to the evaluation of the baseline processing reports Additionally the user should be ready to explain to TxDOT the various aspects of the report and summarize what to look for as far as how to evaluate the quality of the processed vectors These reports should display such items as the elevation cut off angle the type of tropospheric and ionospheric models used a priori and a posteriori baseline errors the common satellites used GDOP and or PDOP values RMS error of the baseline e gt gt gt gt the presence or absence of cycle slips in the data etc Depending on the baseline length use the following specifications for the final acceptable baseline type Table 6 7 Final Acceptable Specifications Baseline Length Desired Final Solution Less than 5 km L1 Only Fixed Solution 5 20 km L1 Only Fixed or L1 L2 IonoFree Fixed Solution 20 50 km L1 L2 IonoFree Fixed Solution 50 90 km L1 L2 IonoFree Fixed or Float Solution Greater than 90 km L1 L2 IonoFree Float Solution GPS User s Manual 6 34 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Comparison of Redundant Baselines Comparison of redundant baselines is an excellent way of detecting blunders in a network There are two 2 types of redundant baselines to consider
146. surveyor must also follow the TxDOT redundancy requirements see Section 6 of this chapter RTK for Topographical Surveys and the equipment manufacturer s prescribed methods Real time surveying technology may utilize single or dual frequency L1 L2 techniques for initialization but the subsequent RTK survey is accomplished using only the L1 carrier phase frequency Therefore all RTK surveys are currently subject to the limitations of the L1 frequency which is ten 10 kilometers from the base station There may be circumstances where this maximum range may be extended Permission to extend this range will be extended at the TxDOT project surveyor s discretion Radio transmission and cell phones are the most common way of providing the communication link between the base and rover GPS User s Manual 6 13 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Section 6 Field Survey Operations and Procedures Overview Field survey operations should be performed using the manufacturer s recommended receiver settings and observation times Operations under adverse conditions such as under a tree canopy or around urban environments where multipath conditions are high may require longer observation times than specified by the manufacturer TxDOT Survey Levels As noted in Chapter 3 TxDOT has divided its design grade GPS surveying into seven 7 levels to facilitate understanding
147. the outside corners of the project at a minimum In other words at least one bench mark should be fixed in each of the four 4 quadrants of the survey area such that nearly all of the newly surveyed stations will fall inside a boundary drawn around the outside benchmarks Additional benchmarks inside the perimeter will aid in strengthening the adjustment GPS User s Manual 5 3 TxDOT 8 2005 Chapter 5 Network Design Section 2 Design Features Network Baseline TxDOT recognizes there are arguments for and against the use of dependent trivial baselines in a network TxDOT recommends not using dependent baselines For any given multiple receiver session there are n n 1 2 total vectors possible where n the number of GPS receivers observing simultaneously The number of independent vectors is n 1 Using only the independent baselines prevents adjusting the same observations more than once and misstating the network degrees of freedom in the least squares adjustment makes it easier to troubleshoot and evaluate the network and locate deviant baselines GPS User s Manual 5 4 TxDOT 8 2005 Chapter 5 Network Design Section 2 Design Features Accuracy Standards for Network Baseline For a station to qualify for an accuracy classification network or local it must meet the listed accuracy standards relative to all other stations in the network and or datum whether or not there was a direct connection between them
148. the word Expected is used because the values given are estimates Table 3 1 Expected Survey Accuracies 20 for NGS Control Positional Component FBN CBN UDN Height 2cm Height 5cm Horizontal Position lcm various lcm 2cm Ellipsoidal Height 2cm various 2cm 5 cm Orthometric Height 3 cm various 2 cm 5 cm The table below provides positional accuracy history Table 3 2 History of Positional Accuracy 20 for NGS Control Network Time Span Network Accuracy Local Accuracy NAD27 1927 1986 10 meters First Order 1 100 000 NAD83 1986 1991 1 meter First Order 1 100 000 HARN 1991 1997 0 1 meter B Order First Order 1 1 000 000 A Order 1 10 000 000 CORS 1996 Present 0 01 meter 0 01 meter The best value NGS has so they are assumed to be zero Federal Geodetic Data Committee FGDC Standards Based on the Geospatial Positioning Accuracy Standards the FGDC STD 007 1998 Part 2 Standards for Geodetic Networks prepared by the FGDC the following accuracy standards supercede and replace the accuracy standards found in FGCC 1984 and FGCC 1988 see Appendix A References The classification standard for geodetic networks is based on accuracy GPS User s Manual 3 5 continued TxDOT 8 2005 Chapter 3 Accuracy Standards Section 3 Local and Network Accuracy Federal Geodetic Data Committee FGDC Standards continued The table of accuracy standards
149. thing of one station in the area and the azimuth from this selected station to an adjacent station horizontal A horizontal is a point with horizontal coordinate accuracy only The control point elevation or ellipsoid height is of a lower order of accuracy or is unknown horizontal distance A horizontal distance is the distance between two points computed horizontally from the elevation of either point horizontal position A horizontal position is a point with horizontal coordinates only HTDP Horizontal Time Dependent Positioning model HTDP is a computer database and interpolation program developed by NGS to predict horizontal displacements between coordinate points over time The program can work backwards in time where it includes earthquake parameter or forward in time where only the secular motion is analyzed hub A hub is a wooden stake set in the ground with a tack or other marker to indicate the exact position A guard stake protects and identifies the hub GPS User s Manual B 12 TxDOT 8 2005 Appendix B Glossary I independent An independent is the subnetworks observations and control points not connected by geometry or errors This term is the opposite of correlated independent baseline An independent baseline is a non trivial baseline Those vectors determined from differencing common phase measurements only once For any given session there are n 1 independent vectors where n is the number
150. tical geodetic data of this sample data sheets An RPLS signature and seal is recommended for data sheets for Level 1 and Level 2 GPS monuments GPS User s Manual 6 5 TxDOT 8 2005 Chapter 6 GPS Survey Specification Co No hEBcoso0m an County Name Anderson Andrews Angelina Aransas Archer Armstrong Atascosa Austin Bailey Bandera Bastrop Baylor Bee Bell Bexar Blanco Borden Bosque Bowie Brazoria Brazos Brewster Briscoe Brooks Brown Burleson Burnet Caldwell Calhoun Callahan Cameron Camp Carson Cass Castro Chambers Cherokee Childress Clay Cochran Coke Coleman Collin Collingsworth Colorado Comal Comanche Corcho Cooke Coryell Cottle Crane Crockett Crosby Culberson Dallam Dallas Dawson Deaf Smith Delta Denton DeWitt Dickens Dirmit Co No 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 92 93 94 95 96 98 99 100 101 102 103 104 126 County Name Donley Kenedy Duval Eastland Ector Edwards Ellis El Paso Erath Falls Fannin Fayette Fisher Floyd Foard Fort Bend Franklin Freestone Frio Gaines Galveston Garza Gillespie Glasscock Goliad Gonzales Gray Grayson Gregg Grimes Guadalupe Hale Hall Hamilton Hansford Hardeman Hardin Harris Harrison Hartley Haskell Hays Hemphill Henderson Hidalgo Hill Hockley Hood Hopkins Houston Howard Hudspeth Hunt Hutchinson Irion Ja
151. tinued GPS User s Manual 6 37 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Loop Closure Reports continued f In any component X Y Z the average misclosure in terms of loop length should not exceed this value in terms of parts per million ppm To calculate this take the sum of all of the loop closure ppm s and divide by the number of loops to yield the average loop closure in ppm s GPS User s Manual 6 38 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Data Adjustment Analysis The purpose of a least squares adjustment is to estimate and remove random errors provide a single solution even when there is redundant data minimize corrections made to the observations detect blunders and large errors and generate information for analysis including estimates of precision The network adjustment occurs in two major steps The first step is the minimally constrained or free adjustment which acts as a quality control check of the user s observations The purpose of the minimally constrained adjustment is to check the internal consistency of the network detect blunders or ill fitting observations and obtain accurate observation error estimates The second step is the fully constrained adjustment The purpose of the fully constrained adjustment is to reference the network to existing control datum verify existing control produce network transforma
152. tinued This manual uses and or references specific information from the following publications 1989 Federal Geodetic Control Subcommittee FGCS document DRAFT Geometric Geodetic Accuracy Standards and Specifications for Using GPS Relative Positioning Techniques the 1998 NOAA Technical Memorandum NGS 58 Guidelines for Establishing GPS Derived Ellipsoid Heights the May 15 2000 Preliminary DRAFT Guidelines for Geodetic Network Surveys Using GPS and numerous other federal state guidelines and specifications listed in Appendix A References GPS User s Manual 2 9 TxDOT 8 2005 Chapter 3 Accuracy Standards Contents Section Overview unused diene nha ea ele eed 3 2 Section 2 GPS SURVEY ACCUTANE id dida 3 3 Section 3 Local and Network Accuracy ii A AA an db 3 4 Section 4 Standards and Specifications ida 3 11 3 1 TxDOT 8 2005 GPS User s Manual Chapter 3 Accuracy Standards Section 1 Overview Section 1 Overview Summary This chapter provides concepts guidelines and methodologies associated with TxDOT s GPS survey accuracy standards This chapter also contains guidelines intended to assist users with achieving consistency and accuracy using GPS dynamic technologies GPS User s Manual 3 2 TxDOT 8 2005 Chapter 3 Accuracy Standards Section 2 GPS Survey Accuracy Section 2 GPS Survey Accuracy Overview The accuracy of classical triangulation network survey
153. tion parameters optional and obtain accurate coordinate error estimates Both steps are required to obtain a complete adjustment and to provide confidence in the results Minimally Constrained Adjustment A minimally constrained adjustment MCA is an adjustment with only one control point held fixed in the survey network Holding one control point fixed shifts observations to the correct location within the chosen datum Not fixing a control point forces the software to perform a free adjustment A free adjustment is accomplished by minimizing the size of the coordinate shift throughout the network This equates to a mean coordinate shift of O zero in all dimensions A minimally constrained or free adjustment acts as one quality control check on the network This adjustment helps to identify bad observations in the network If an observation does not fit with the rest of the observations it is highlighted as an outlier The minimally constrained or free adjustment also checks on how well the observations hold together as a cohesive unit All minimally constrained adjustments must be performed in the WGS 84 datum Since all GPS observations are made on the WGS 84 datum the adjustment of the observations should be tied closely to the WGS 84 datum Realistic error estimates for tribrach centering and H I measurement should also be factored into the minimally constrained adjustment continued GPS User s Manual 6 39 TxDOT 8 2005
154. tire session In that case the satellite should be eliminated from the solution then resolve the baseline Another way to eliminate high SNR on satellites low to the horizon is to raise the elevation mask for the baseline solution If the length of the session is short perhaps too short try a baseline solution with a shorter epoch than normal e Ifthe default on the baseline solution is thirty 30 seconds try fifteen 15 seconds This will increase the number of single double and triple differences needed to resolve the baseline If all the above suggestions fail resolve the baseline using a more precise ephemeris than was started with Asa last resort the baseline must be re observed Be sure to select a time period different from the original observed time Look at sky plots and select a time with many satellites and an area free of obstructions GPS User s Manual 6 33 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Baseline Analysis Prior to performing a least squares adjustment on the network or traverse the GPS processed baselines should be analyzed for possible errors using three 3 tools evaluation of the results of each individual baseline comparison of all redundant baselines generation and analysis of loop closure reports To facilitate the error detection process vector data should be displayed with the horizontal and vertical components separated Table 6 8
155. to several hours control or deformation surveys that require the highest levels of precision and repeatability occupied station An occupied station is a traverse or triangulation station over which a theodolite or an engineer transit is set up for the measurement of angles at this station It is also a station at which angles have been measured offset line An offset line is a supplementary line close to and usually parallel to a main survey line to which it is referenced by measured offsets When the line for which data is desired is in such position that it is difficult to measure over it the required data is obtained by running an offset line in a convenient location and measuring offset from it to salient points on the other line order of accuracy An order of accuracy is a mathematical ratio defining the general accuracy of the measurements made in a survey The orders of accuracy for surveys are divided into four classes named first order second order third order and fourth order origin An origin is the intersection of axes in a coordinate system It is the point of beginning orthometric height An orthometric height is the distance between a point and the surface of the geoid It is usually called the elevation OTF search method On the fly OTF search method is a GPS baseline processing whether real time or postprocessed requires fixed integer solutions for the best possible results See integer sear
156. tric Height Classification Range 95 Confidence Level in Meters Range VIII 0 100 0 200 Range IX 0 200 0 500 Range X 0 500 1 000 Range XI 1 000 2 000 Range XII 2 000 5 000 Range XIII 5 000 10 000 Range XIV gt 10 000 Ranges larger than XIII will be developed jointly with other subcommittees within FGDC GPS User s Manual 3 10 TxDOT 8 2005 Chapter 3 Accuracy Standards Section 4 Standards and Specifications Section 4 Standards and Specifications Standards and Specifications Issues There are two issues which are significant within the manuals standards and specifications First least squares analysis is the primary process by which the stated project conclusions are justified However this process is only valid with sufficient redundancy and correct assumptions made regarding the probability of errors Second the processing of raw GPS observables has been the subject of much innovation and experimentation This trend is certain to continue as GPS technology is extremely dynamic and changing constantly It is the responsibility of the professional in charge to employ techniques which are appropriate for the project and to provide verification that the stated conclusions are valid The use of these standards and specifications are recommended and do not relieve the surveyor from making decisions or using professional judgment during the co
157. trol point i e the adjacent stations directly tied to the control point The network accuracy of a control point is a value that represents the uncertainty in the coordinates of the control point with respect to the geodetic datum at the 95 percent confidence level e For National Spatial Reference System NSRS network accuracy classification the datum is considered to be best expressed by the geodetic values at the Continuously Operating Reference Stations CORS supported by NGS By this definition the local and network accuracy values at CORS sites are considered to be infinitesimal i e to approach zero Local accuracy is best adapted to check relations between nearby control points for example a surveyor checking closure between two NSRS points is most interested in a local accuracy measure Positional Tolerance and Associated Coordinates On the other hand someone constructing a GIS will often need some type of positional tolerance associated with a set of coordinates Network accuracy measures how well coordinates approach an ideal error free datum The following two tables are reproduced from National Geodetic Survey s Guidelines for Geodetic Network Surveys Using GPS 5 15 00 Preliminary DRAFT continued GPS User s Manual 3 4 TxDOT 8 2005 Chapter 3 Accuracy Standards Positional Tolerance and Associated Coordinates continued Section 3 Local and Network Accuracy In the following table
158. ts outlined in Tables 4 1 5 1 6 2 6 6 and 6 8 of this manual to include the following requirements 4 referenced to three 3 or more CORS FBN CBN or Level 1 control densification horizontal control stations located in three 3 or more quadrants relative to the survey project area referenced to four 4 or more benchmarks second order or better in four 4 quadrants for orthometric heights all new stations are established by two 2 or more independent baselines all stations must be occupied a minimum of two times baselines have a fixed integer double difference solution or adhere to the manufacturer s specifications for baseline lengths exceeding the fixed solution criteria 1 e float solution may be the best solution for baselines in excess of 100 km depending on manufacturer specifications and recommendations any station pair used as azimuth or bearing reference for use with conventional survey measurements during the course of any other survey level should be included in a network or measured radially with a minimum of two 2 independent baselines the primary project control network must be a geometrically closed figure therefore single radial spur lines or side shots to points are not acceptable radial lines are acceptable only for distant azimuth marks GPS User s Manual 6 16 TxDOT 8 2005 Section 6 Field Survey Operations and Chapter 6 GPS Survey Specification Procedures Level 3 Surveys
159. twenty 20 kilometers use either the rapid or the precise ephemerides continued GPS User s Manual 6 29 TxDOT 8 2005 Chapter 6 GPS Survey Specification Orbit Ephemeris continued Section 7 Data Processing All of the ephemerides are available in the SP3 format at the following Web site http igscb jpl nasa gov components prods_cb html The naming convention of the orbit files are as follows Table 6 4 Orbit Files Naming Convention Example lgexwwwd_hh sp3 where x type of orbit p precise r rapid u ultra rapid where Www GPS week where d Day of week 0 Sunday where hh UTC hour The following table illustrates ephemeris types their availability and accuracy Table 6 5 Ephemerides Availability and Accuracy Ephemeris When Product Accuracy Type Available Precise 13 days 5 cm Rapid 17 hours 5 cm Ultra Rapid 3 hours 5cm Predicted Real time 10 cm Broadcast Real time 200cm In the event that the baseline processing software only accepts the binary orbit file type EF18 the following web site will translate the ASCII SP3 format file http www ngs noaa gov GPS GPS html GPS User s Manual 6 30 continued TxDOT 8 2005 Chapter 6 GPS Survey Specification Orbit Ephemeris continued Section 7 Data Processing The table below lists the requirements for the use of the various types of ephemerides Table 6 6 Baseline
160. twork or local accuracy level a GPS project must be connected to sufficiently accurate and well distributed existing control All of the control stations to which the network will be constrained must have positions known on the NAD83 datum Control stations of the state HARN adjustment are generally used however certain special projects may have a legitimate need for another geodetic reference Use the appropriate datum adjustment as recommended by the TxDOT district surveyor or survey coordinator The minimum number of horizontal and vertical constraints is stated in Table 5 1 with their location being distributed in different quadrants relative to the center of the project Where existing NGS or TxDOT horizontal and or vertical control on a common datum and epoch is available all such stations lying within a few kilometers of the survey s boundaries should if possible be included in the survey if they meet the horizontal accuracy requirements Second order or better is generally required for vertical Orthometric Height Requirements for orthometric height constraints are dependent upon geoid slope project extent desired accuracy and the density of the gravity database These issues are addressed under the subsection Orthometric Height Determination in Chapter 6 Section 7 In general vertical control for Level 1 and Level 2 networks require a minimum of 4 preferably 5 published vertical control stations They should be situated on
161. types Solution types refer to a description of both the data and techniques used to obtain baseline solutions from GPS measurements Typical solution types include descriptions such as code float and fixed These describe techniques used by the baseline processor to obtain a baseline solution Solution types also may include descriptions such as L1 L2 wide lane narrow lane or ionospheric free These describe the way the GPS measurements are combined to achieve particular results For more information see the references on GPS processing for a more in depth discussion of these terms and techniques slope distance A slope distance is the distance in the plane parallel to the vertical difference slope between the points SNR Signal to Noise Ratio standard deviation A standard deviation is a standard error Surveying applications use the conventional formula for sample standard deviation Standard deviation is a measure of the strength of a satellite signal SNR ranges from 0 no signal to around 35 standard error A standard error is a statistical estimate of error according to which 68 percent of an infinite number of observations will theoretically have absolute errors less than or equal to this value standard error of unit weight A standard error of unit weight is a measure of the magnitude of observational residuals in an unit weight adjusted network as compared to estimated pre adjustment observational errors
162. ubbings of stations 1f required Level 1 completed data sheet for each point surveyed as a Level 1 station see Chapter 6 Figure 6 2 TxDOT Control Point Data Sheet and Figure 6 3 Sample Project Specifications Control Point continued GPS User s Manual 8 3 TxDOT 8 2005 Chapter 8 Project Documentation and Deliverables to TxDOT Section 2 Project Documentation Printed Technical Reports continued survey field notes to include a sketch of each point surveyed as a Level 2 or 3 station list of the NSRS points and TxDOT reference stations observed in the survey whether used in the final adjustment or not An ASCH file of final coordinates by station including notes on datum geoid model epoch units etc as outlined in Chapter 7 The most often requested format is name northing easting elevation feature code if used an ASCII file of the final position information same as above in lat lon 4 SDMS format CAL or PAC file If it is necessary documentation variation from these specifications may be used Digital Data In addition to the printed material the surveyor in responsible charge of the project should submit the following digital data on a recordable read only CD raw GPS files in Trimble DAT or RINEX format should be one file per individual observation and files should be able to be matched to the appropriate observation log sheet zipped or archive file of the processing adjustment progra
163. ubsidence disturbed monuments or dissimilar control sources must not be allowed to contaminate the computed trend parameters continued GPS User s Manual 6 42 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Orthometric Height Determination continued Caution Failure to exercise extreme caution in this step can introduce significant errors into the computed heights For instance a local area of subsidence if not detected could be entirely absorbed within the rotation parameters for the bias group Errors in the geoid model or GPS ellipsoid heights could be similarly masked The analysis of the geoid modeling must identify the magnitude of vertical discrepancies and apply corrections to the geoid model and vertical constraints which are appropriate to its source This can only be accomplished with abundant levels of redundancy and careful analysis The following table provides additional requirements specific to the geoid modeling process In addition to using the latest geoid model the surveyor should use the latest National Vertical Datum NAVD88 height values to control the project s adjusted heights Also recommended is that the surveyor be familiar with NGS guidelines for establishing GPS derived ellipsoid heights when performing GPS surveys continued GPS User s Manual 6 43 TxDOT 8 2005 Chapter 6 GPS Survey Specification Section 7 Data Processing Orthometric Hei
164. ued Guard Fence G F Guard Fence Concrete G F Guard Post F Guardrail Cable G F Gravel Road G G island G G Lane Line G G Point of Curvature G Point of Continuous Curve G Private Entrance G F Point of intersection G Parking Lot G G Point on Curve G Point on Tangent G Point of Reverse Curve G Point of Tangency G Radius Point G Shoulder G S Slab G G Tractor Crossing G G Bridge Elements All Features Go To Zone 2 UNO Bridge Armor Joint G G Bridge Approach Slab Zone 1 S G Bridge Bent G G Bridge Centerline G G Bridge Curb G G Bridge Elements G G Bridge Gutter G G Bridge Overhang G G Bridge Stripe Solid G G Bridge Stripe Dashed G G Bridge Rail Metai Concrete G G BSE Bridge Spot Elevation G G BSW Bridge Sidewalk G G BTR Bridge Truss Railroads G G DECK Bridge Deck G G RAILROAD Railroad Tracks G G Railroad Control Box F Railroad Milepost F Railroad Signal Standard F Railroad Switch F Railroad Crossing Sign F Signai Span Wire Support Mast Arm F TRAFFIC Cabte in Pavement Detector G F Directional Arrow Pavement Marking G F High Mast Lighting Tower F Light Base F Small Light Pole F Match Line G Marker Post F Pull Box F Paint Stripe Solid G G Pedestrian Signal Box F Paint Stripe Dashed G G Paint Stri
165. urse of the field survey and the subsequent data processing to obtain the desired results Carefully document the procedures techniques and results for every step Accuracy Levels and Specifications Experience has shown that current receivers and software have the capability to achieve geodetic quality accuracy levels under certain conditions and restrictions Specifications for performing control surveys using kinematic techniques require greater observational and occupational redundancies and checks than usually specified by the manufacturers The specifications provide sufficient observational and occupational redundancy to detect blunders and quantitatively demonstrate accuracy achievement for a survey The accuracy reporting requirements of this document are in accordance with accuracy reporting requirements of the Federal Geographic Data Committee s Geospatial Positioning Accuracy Standards FGDC STD 007 1998 GPS User s Manual 3 1 TxDOT 8 2005 Chapter 3 Accuracy Standards Section 4 Standards and Specifications Statistical Analyses In accordance with new federal positioning standards these specifications rely heavily on the use of statistical analyses to determine the accuracy of a GPS survey Regardless of how the observations for a particular survey were obtained the completed survey must provide the following information elimination or reduction of known and potential systematic error sources suff
166. version of a Metric to US Survey Foot or visa versa b SPC zones to adjoining SPC zones c UTM to SPC s and d Latitude Longitude to SPC s In addition to these strictly mathematical conversions they provide useable combined adjustment factors CAF at the specific location of a point if the elevation is included in the input GPS User s Manual 7 5 TxDOT 8 2005 Chapter 8 Project Documentation and Deliverables to TxDOT Contents Section L OVAs iaa cuida 8 2 Section 2 Project Documentation id iii 8 3 section 3 Project Delivetables 2uc c eee iin ae Me AIRS 8 6 GPS User s Manual 8 1 TxDOT 8 2005 Chapter 8 Project Documentation and Deliverables to TxDOT Section Overview Section 1 Overview Purpose The purpose of this chapter is to provide guidelines and policy under which TxDOT employees and contractors prepare project documentation and deliverables Scope TxDOT requirements for project documentation and deliverables are outlined in this chapter Specifications on technical reports digital data control point data sheets and validation surveys are presented GPS User s Manual 8 2 TxDOT 8 2005 Chapter 8 Project Documentation and Deliverables to TxDOT Section 2 Project Documentation Section 2 Project Documentation Printed Technical Reports A technical report must be prepared and submitted to the TxDOT district surveyor by the surveyor in responsible charge as documentatio
167. work Accuracy TxDOT Standards continued Equation for determining maximum relative positional error at the 95 confidence level s e Elda px10 Where s Maximum allowable relative positional error m at the 95 20 confidence level e Base error in meters m p Parts per million ppm d Distance in meters m New NGS GPS Accuracy Standards Table 3 6 NGS Accuracy Standards Classification Minimum Geometric Accuracy Standard at 2 o Less than or equal to AA 0 003 m 1 100 000 000 A 0 005 m 1 10 000 000 B 0 008 m 1 1 000 000 First 0 010 m 1 100 000 Second Class I 0 020 m 1 50 000 Second Class II 0 030 m 1 20 000 Third 0 050 m 1 10 000 The following table provides the classification range and confidence levels for accuracy standards Table 3 7 NGS Accuracy Standards for Horizontal Position Ellipsoid Height and Orthometric Height Classification Range 95 Confidence Level in Meters Range 0 Reserved for CORS Range I lt 0 001 Range II 0 001 0 002 Range III 0 002 0 005 Range IV 0 005 0 010 Range V 0 010 0 020 Range VI 0 020 0 050 Range VII 0 050 0 100 continued GPS User s Manual 3 9 TxDOT 8 2005 Chapter 3 Accuracy Standards TxDOT Standards continued Section 3 Local and Network Accuracy Table 3 7 NGS Accuracy Standards for Horizontal Position Ellipsoid Height and Orthome

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