GPS navigation corrections (T11)
Contents
1. See Vector dataset field aliases in INTREPID database file and data structures R05 for more information about aliases Open Input dataset Use this to specify the line dataset you wish to process 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 8 Library Help Top Library Help Top 4 Back gt Open Input Ranger Use this to specify the GPS differential processing data to be merged with the dataset that you are correcting This is currently a text file produced by the Ranger GPS differential processing software See GPS navigation corrections theory for an explanation Load Options If you wish to use an existing task specification file to specify the GPS navigation correction process use this menu option to specify the task specification file required INTREPID will load the file and use its contents to set all of the parameters for the GPS navigation correction process See Displaying options and using task specification files for information about task specification files Save Options If you wish to save the current GPS navigation correction file specifications and parameter settings as a task specification file use this menu option to specify the filename and save the file See Saving the corrections for more information Sample list of aliases Note These alias definitions appear in the INTREPID standard information isi file in the following for2. Use the Processes menu to select the correction and calculations to be performed on the dataset File Processes Options Help WGPS Differential Doppler Infill WWGS84 to AGD84 wag Parallax Filter Terrain WHeight Infill You can select any or all of the following corrections or processes See GPS navigation corrections theory for more detailed explanations To turn on the processes that you require choose the corresponding menu options so that ticks appear against them in the menu To turn off a process choose its menu option again so that it has no tick against it GPS Differential Update the navigation data with the GPS differential processing data Doppler Infill Use Doppler data to fill gaps in the navigation data WGS84 to AGD84 Transform the navigation data from the WGS84 datum to the AGD84 datum Mag Parallax Adjust the navigation data to coincide with the position of the magnetometer as opposed to the position of the GPS receiver Filter Smooth the navigation data using a low pass convolution filter to remove any high frequency noise Terrain Generate digital terrain data height of the ground above or below the datum WGS84 or AGD84 depending on the WGS84 to AGD84 setting see above INTREPID combines GPS Height from the GPS differential processing data with the Ground Clearance data to derive the Terrain Height The Terrain field is the only form of vertical georeference available usin
3. of the display If you have zoomed out to view the whole display the small square may occupy the whole of the large square and may therefore not be visible Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 6 Library Help Top lt 4 Back gt Specifying input and output files To use GPS navigation correction you must specify the line dataset to be corrected and identify the field files required for the process You must identify the field files by giving them aliases See Vector dataset field aliases in INTREPID database file and data structures R05 and Sample list of aliases below This section lists the aliases required and has instructions for specifying required files Choose the options as required from the File menu Fife Processes Options Help Open Input Dataset In each case INTREPID displays an Open dialog box Use the directory and file selector to locate the file you require See Specifying input and output files in Introduction to INTREPID R02 for information about specifying files Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Library Help Top GPS navigation corrections T11 7 lt 4 Back gt Vector dataset notes INTREPID will identify fields from the dataset aliases for the process The dataset must have the following aliases identifying appropriate fields Libra
4. D performs the survey distance calculation displaying the flight paths and the report and saving the report if required Help You can use the help menu to display help text on the topics shown in the menu illustration below File Processes Options Help GPS fix File Options Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 11 Library Help Top lt 4 Back gt Exit To exit from GPS Navigation Corrections choose Quit from the file menu Displaying options and using task specification files Displaying options gt gt To display the current task specifications Choose Show from the GPS Navigation Corrections window INTREPID displays the current file specifications and parameter settings in a report window Using task specification files You can store sets of specifications for GPS Navigation Corrections in task specification job files gt gt To create a task specification file with the GPS Navigation Corrections tool 1 Specify all files and parameters 2 If possible execute the task choose Apply to ensure that it will work 3 Choose Save Options from the File menu Specify a task specification file INTREPID will add the extension job INTREPID will create the file with the settings current at the time of the Save Options operation For full instructions on creating and editing task specification files see INTREPID task sp
5. INTREPID User Manual GPS navigation corrections T11 1 Library Help Top 4 Back gt GPS navigation corrections T11 Top The GPS Navigation Corrections tool merges the Global Positioning Satellite GPS data as recorded on the survey aircraft and the differential processed GPS data generated by the Ranger software It applies other selected corrections and produces the final navigation data at the position of the magnetometer sensor in the aircraft It also computes the height of the ground above or below the WGS84 or AGD84 datums giving digital terrain data The documentation included here will describe for you the capabilities of an INTREPID GPS Navigation Corrections tool The tool can be adapted for real time use or used for post processing Customising the GPS corrections tool If your GPS equipment is a brand other than Ranger or you require automatic transformation of data to some other datum we can assist you to create a customised INTREPID GPS Navigation Corrections tool This will be able to correct data from your aircraft or ship and differential GPS ground station according to your practices and specifications Please contact us for further information GPS navigation corrections theory GPS Differential corrections Library Help Top The GPS data as recorded on the aircraft has built in errors created according to US government policies GPS differential processing software uses GPS readings from a
6. base station to remove these errors GPS differential processing requires a minimum of 4 satellites When there are less than 4 satellites available no differential data is produced Post processing option After the flight you can merge the inflight and base station data using the GPS differential processing software This produces an ASCII file containing updated navigation data at a sample interval of 5 seconds Correcting navigation data The inflight GPS device records navigation data typically every second To correct all of the navigation data you need to interpolate the corrections within each 5 second interval To obtain the corrected values INTREPID 1 Calculates the difference between the inflight data and the differential data at each point for which they both exist i e every 5 seconds 2 Regards these differences as corrections to be applied to the inflight data 3 Linearly interpolates the corrections for each point within the 5 second interval 4 Applies these corrections to the inflight data producing corrected navigation data Correcting for rapid variations Rapid variations in the corrections may reduce the accuracy of the corrections To remedy this INTREPID also 1 Searches for abrupt steps in the original GPS data especially the survey height field 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 2 Library Help Top lt 4 Back gt 2 Instead
7. corrections T11 3 Library Help Top lt 4 Back gt Filling GPS height data gaps using air pressure and temperature data You can fill gaps in the GPS height data from the air pressure and temperature data recorded by the survey aircraft WGS84 to AGD84 conversion GPS data relates to the WGS84 datum Most Australian users will require their resulting dataset to relate to the AGD84 datum Automatic transformation to this datum would be a useful feature of a GPS corrections process Terrain height above or below ellipsoid You can use the GPS height distance to WGS84 ellipsoid and the ground clearance to derive the terrain height distance from the ground to the ellipsoid If you convert the GPS height to height above some other ellipsoid the terrain height will be relative to the other datum Using the GPS Navigation Corrections tool This tool is an INTREPID module which performs the operations described above It currently processes the data one flight at a time so you will usually need to use it several times to process your whole survey gt gt To use GPS Navigation Corrections with the INTREPID graphic user interface 1 Choose Navigation from the Utility menu of the Project Manager or use the command gpsnav exe INTREPID displays the GPS Navigation Corrections window i xj Intrepid GPS Navigation Tool Y3 Beta File Processes Options Heip 2 Ifyou have previously prepared file specifications and para
8. ecification job files R06 gt gt To use a task specification file in an interactive GPS Navigation Corrections session Load the task specification job file File menu Load Options modify any settings as required then choose Apply gt gt To use a task specification file for a batch mode GPS Navigation Corrections task Type the command gpsnav exe with the switch batch followed by the name and path if necessary of the task specification file For example if you had a task specification file called surv_gps job in the current directory you would use the command gpsnav exe batch surv_gps job Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 12 Library Help Top lt 4 Back gt Task specification file example Here is an example of a GPS Navigation Corrections task specification file Process Begin Name gpsnav Parameters Begin DataBaseDirectory disk1 surv FL591 SEC File Begin RangerDifferential disk1 surv rng_591 asc File End FlightNumber 0 DifferentialCorrectiuons No DopplerInfill Yes WGS84toAGD84 Yes MagParallax No Filter No Terrain No HeightInfill No Parameters End Process End Library Help Top 2012 Intrepid Geophysics lt 4 Back gt
9. g this tool Contact our technical support service for information about customising this tool for e Automatic conversion to other datums or Obtaining other vertical georeference 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 10 Library Help Top lt 4 Back gt Height Infill Use pressure and temperature data to fill gaps in the GPS height data and hence the digital terrain data Specifying the flight number GPS Navigation Corrections will currently process only one flight at a time You must specify the flight number before INTREPID can carry out the process gt gt To specify the flight number of the data to be corrected choose Flight from the options menu File Processes Options Help Flight Save corrections INTREPID displays the Flight number dialog box Intrepid GPS Navigation Tool V3 Beta Flight Number Flight number Of La 1 Specify the flight number in the dialog box and choose OK Saving the corrections You can save the values of the GPS differential processing corrections If you turn on the Save Corrections option in the Options menu so that it shows a tick INTREPID will save the corrections in the field files represented by the aliases longcorr and latcorr To turn the option on or off choose it from the menu File Processes Options Heip Flight Save corrections Apply When you choose Apply INTREPI
10. k specification files for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 5 Library Help Top lt 4 Back gt Zooming and panning the display apply Show zoca In Zaca Aut zoca Area You can enlarge and reduce the display zoom in and out and view different parts of it pan gt gt To zoom in and out enlarge reduce To zoom in enlarge the display choose Zoom In at the right edge of the GPS Navigation Corrections window Each time you choose this button INTREPID will enlarge the display by one step To zoom out reduce the display choose Zoom Out at the right edge of the GPS Navigation Corrections window Each time you choose this button INTREPID will reduce the display by one step gt gt To zoom in on a selected area of the display Choose Zoom Area then hold down the left mouse button and drag diagonally corner to corner across the area that you wish to enlarge INTREPID will enlarge the selected region to fill the display area of the window gt gt To pan the display view different parts The Pan zoom indicator at the right of the GPS Navigation Corrections window in the centre consists of a small square within a larger square The large square represents the whole display and the small square the part visible on the screen When you drag the small square to a different part of the large square INTREPID shows the corresponding part
11. mat X Begin Alias wgs84LONG X End Y Begin Alias wgs84LAT Y End Alias list X longitude Y latitude Fiducial FID FlightNumber disk1 survey TRAVERSES flight LineNumber disk1 survey TRAVERSES LINE FiducialFactor disk1 survey TRAVERSES fidFactor DateCode disk1 survey TRAVERSES dateCode MeanAltitude disk1 survey TRAVERSES altitude Bearing disk1 survey TRAVERSES bearing GPStime gpstime GPSdelay gpsdelay Clearance clearance Temperature disk1 survey TEN temperature Pressure disk1 survey TEN temperature DopplerAcross across DopplerAlong along Terrain terrain Longcorr longcorr Latcorr latcorr 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Library Help Top 00001 00002 00003 00004 04096 04097 04098 04099 591 591 591 591 591 591 591 591 GPS navigation corrections T11 Sample of Ranger GPS differential processing data 931010 210035 00 20 32 52 05477 130 20 49 11387 417 816 931010 210040 00 20 32 52 08636 130 20 49 12985 420 020 931010 210045 00 20 32 52 04481 130 20 49 21634 421 009 931010 210050 00 20 32 52 08690 130 20 49 39606 422 437 931011 024310 00 20 32 6 83918 130 21 4 01017 594 225 931011 024315 00 20 31 58 61532 130 20 58 40839 595 870 931011 024320 00 20 31 51 62385 130 20 51 14287 607 551 931011 024325 00 20 31 46 58258 130 20 42 24105 615 929 Specifying the processes to carry out Library Help Top
12. meter settings for GPS Navigation Corrections load the corresponding task specification file using Load Options from the File menu See Specifying input and output files below for information about specifying files If all of the specifications are correct in this file go to step 7 If you wish to modify any settings carry out the following steps as required 3 Specify the line dataset to be corrected and the Ranger GPS differential processing file Use the corresponding options from the File menu See Specifying input and output files below for information about specifying files Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation corrections T11 4 Library Help Top Library Help Top 4 Back gt 4 Specify the flight number to be processed using Flight from the Options menu See Specifying the flight number below 5 Specify the corrections you wish to perform by turning on the options as required in the Processes menu See Specifying the processes to carry out below for details 6 Specify whether or not you wish to save the GPS differential processing corrections as a separate field file Use Save corrections from the Options menu See Saving the corrections below 7 When you have specified files according to your requirements choose Apply INTREPID will apply the corrections to the data and display each line in the GPS Navigation Corrections window as it is pr
13. ocessed It plots the portions of the flight path generated by Doppler infill in red xj Intrepid GPS Navigation Tool V3 Beta 34 23 i E 30 6G 224R om mw yw ary OF Hol a eo Sai TR Si i t l i H l 5 E Dal Ga A BY pp a eo PE 7o SPN aa G Gel ite o 35 53 TF T30 sd Zoom Area When the process has finished you can zoom enlarge an area of the display and pan examine different regions while enlarged See Zooming and panning the display for details 8 Ifyou wish to record the specifications for this process in a task specification job file in order to repeat a similar task later or for some other reason use Save Options from the File menu See Specifying input and output files for information about specifying files 9 Ifyou wish to repeat the process repeat steps 2 8 varying the specifications as required 10 To exit from GPS Navigation Corrections choose Quit from the File menu To view the current set of specifications choose Show from the GPS Navigation Corrections window INTREPID displays them in a separate window See Displaying options and using task specification files for details and an example of a set of specifications You can view Help information by choosing options from the Help menu See Help You can execute GPS Navigation Corrections as a batch task using a task specification job file that you have previously prepared See Displaying options and using tas
14. of interpolating within the interval applies the correction on one side of the step to all inflight values in the interval on that side It then applies corrections correspondingly on the other side of the step thus preserving the step rather than attempting to smooth it Where multiple steps occur it may be impossible to correlate the original GPS data with corrections In this case INTREPID sets the intervening points in the inflight data to null Problems associated with interpolation can lead to small steps in the final data where original steps were not detected If this happens INTREPID can apply a low pass filter over the final navigation data to smooth out steps or spikes Doppler infill corrections The Doppler radar system on the aircraft measures and records the velocity of the aircraft This is part of the navigation system used before GPS became available If there are data gaps in the original navigation data or the GPS differential processed data INTREPID can fill them using the Doppler data INTREPID performs the Doppler infill assuming the corrected GPS data bordering a gap are correct It notes the Doppler data at these bordering points then uses it as a guide for interpolating the navigation data between the points For small gaps of the order of 5 km this is satisfactory We recommend that for gaps approaching 10 km that you acquire the data again rather than perform the infill INTREPID cannot perform Doppler infill f
15. or gaps occurring at the start or end of a traverse line since there is no correct value for calibrating the Doppler data at one end of the gap The Doppler system records velocity as aircraft speed in the flight path direction and across the flight path direction GPS time delay GPS time shift There is a small delay after receiving GPS data while the GPS system calculates a position The length of this delay is a function of the number of satellites in use There must be a correction to compensate for this delay Once the GPS system calculates the position it make this data available to the aircraft acquisition system There is usually a delay to the next fiducial at which the acquisition system can record the data There must be a correction to compensate for this delay GPS receiver to magnetometer distance correction Library Help Top The GPS data gives the position of the GPS receiver The magnetometer is some distance away behind the aircraft It is also the recording instrument most likely to have significant position errors For more accurate navigation data you must adjust the GPS data to coincide with the location of the magnetometer A typical example is the AGSO survey aircraft where the magnetometer is 11 4 metres behind the GPS receiver INTREPID uses this distance for the correction known as the magnetometer parallax correction 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual GPS navigation
16. ry Help Top Alias Field FlightNumber Flight identification number LineNumber Traverse line identification number FiducialFactor Time in seconds that corresponds with a fiducial interval DateCode Date of flight in the format DDMMYY MeanAltitude Nominal height above sea level Bearing Nominal bearing in degrees of traverse line measured positive east of north Fiducial Fiducial data GPStime GPS time in 1 100 seconds since midnight on the previous Sunday GPSdelay GPS delay time in 1 100 seconds GPStimeShift GPS time shift in 1 100 seconds Clearance Ground clearance in metres Temperature The temperature data recorded by the survey aircraft Pressure The air pressure data recorded by the survey aircraft DopplerAcross Doppler data across the flight path in metres DopplerAlong Doppler data along the flight path in metres X Longitude to be corrected Y Latitude to be corrected INTREPID updates X and Y with the corrected values Terrain Height of the ground above or below the datum WGS84 or AGD84 INTREPID updates this field if you have specified that it should calculate digital terrain data Longcorr Correction made to longitude Latcorr Correction made to latitude INTREPID updates the Longcorr and Latcorr fields if you have specified that the GPS corrections from the differential processing should be saved See Saving the corrections
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