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Gridding (T22a) - Intrepid Geophysics

1. For full details of these process see articles by Brindt and Hauska 1985 and Fitzgerald Yassi and Dart 1997 It is possible to tune Trend Spline gridding to accept or reject solutions based upon reliability of data in one direction versus another If this capability is of interest to you please contact our technical support service Trend spline parameters Minimum Maximum Scan Distance See Gridding Method Bi Cubic Spline for an explanation of this parameter Nominal Bearing See Gridding Method Bi Cubic Spline for comments about this parameter Rotate Line Data See Gridding Method Bi Cubic Spline for comments about this parameter Spline Type See Gridding Method Bi Cubic Spline for an explanation of this parameter Trend Variance Factor The trend variance factor is the minimum level for significance of local variations The number of trend points generated is very sensitive to the value of this parameter Its default value is 1 Z unit You can change the value of the trend variance factor if you are using a task specification file for your gridding process Edit the task specification job file changing the value in the Trend _Variance_Factor line according to your requirements e g Trend_Variance_Factor 2 See Task specification job files in Gridding for further information Recording the additional trend points Trend picker window size INTREPID applies a high pass filter to the data before e
2. gt Minimum Curvature Parent topic Grid Refinement tab Library Help Top The Minimum Curvature method progressively examines each interpolated cell in the grid in relation to its immediate neighbours and changes its value based on the value of the neighbours The aim of the minimum curvature method is to produce a smooth surface of grid values Working in both directions it adjusts cell values using a second derivative calculation based on the differences between the values of the adjacent cells It does not modify the original data points A note about this method and the new Spherical Linear Interpolation method for Full tensor data These two methods are largely incompatible with each other Minimum Curvature is designed to calculate from a scalar measure of a potential field the curvature gradients in particular Txx Tyy Tzz and to use a finite difference method to force the residual of the Trace Txx Tyy Tzz to zero in all parts of the grid A Full Tensor grid already contains these curvature gradients and so the above ideas no longer hold An alternative formulation based on forcing incremental derivatives of the horizontal components into a compliant relationship is in preparation and will be released in Intrepid shortly INTREPID uses a relaxation factor to accelerate the interpolation process As INTREPID calculates a new value for each interpolated cell it multiplies the difference between the old and adjusted valu
3. job file specifies Input and output grid filenames Griddng parameters Notes You can modify the following operations or parameters only by editing a task specification file You can modify the relaxation factor in the minimum curvature process See Minimum Curvature for details Change the value in the Relaxation_Factor line according to your requirements e g Relaxation_Factor 1 325 e You can modify the Trend_Variance_Factor See Gridding Method Trend Spline for details Note The Trend Spline method is no longer supported in the gridding tool Finding out more about task files and batch processing mode Use the following references Introduction to INTREPID auxiliary files INTREPID Auxiliary files in INTREPID database such as task files file and data structures R05 Structure syntax and use of INTREPID task INTREPID task specification job files R06 files Running INTREPID in batch processing How to start INTREPID Overview in Introduction mode to INTREPID R02 Main block structure of a Gridding task file Library Help Top The following table shows the main block structure of a Gridding task file See for more details Block definition Contents Process Begin Task file outer block athe Tool name and date stamp Parameters Begin Parameters block Filenames Parameters Parameters End End Process End End 2012 Intrepid Geophysics 4 Back
4. 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 26 Library Help Top lt 4 Back gt Gridding parameters for line datasets Process Grid Extrapolate Nominal Bearing Rotate Search Box Cell Cell Line Radius Iterations Size Data Grid initialisation yes yes if required for acquisition line identification Nearest Neighbours yes yes Bi Cubic Spline yes yes yes ON yes Variable Density yes yes no yes Box Filter yes yes if required for yes acquisition line identification Library Help Top for oblique line datasets Gridding parameters for point datasets Process Grid Cell Size Extrapolate Cell Box Iterations Grid initialisation yes yes Nearest Neighbours yes yes Variable Density yes yes yes Recording the cell centroid and original data point positions You can save the cell centroids and the exact positions of original data points selected for use the sample points We have provided this option for technical auditing of the gridding process gt gt To save the cell centroid and sample point exact positions Assign a value to the system parameter INTREPID_ HONOUR_ORIGINAL before processing INTREPID will save a point dataset called honour containing a record of each sample point Each data point recorded will have two sets of coordinates The coordinates of the corresponding cell centroid and The e
5. Back gt INTREPID User Manual Gridding T22a 20 Library Help Top Point quality Parent topic Input tab lt 4 Back gt Acquisition lines identified by Nominal Bearing If you do not specify a line type field but you do specify a Nominal Bearing estimate of the strike orientation of the acquisition lines INTREPID will identify the traverse lines oriented within 22 of the Nominal Bearing as acquisition lines INTREPID uses the start and end points of a traverse line to calculate its strike If you want to use the Nominal Bearing setting to identify the acquisition lines but do not know their strike INTREPID can calculate the average strike of the dataset for you See Nominal Bearing for instructions If you do not identify acquisition lines If you deselect the tick box next to Acquisition lines identified by INTREPID will grid all traverse line data This section is for point dataset gridding only If there is a PointType alias or you have specified a point type field INTREPID will grid only those points for which the point type 1 If you have not specified a point type field INTREPID will grid using all points Nominal Bearing Parent topic Input tab Library Help Top This section is for line dataset gridding only If you are gridding a field from a line dataset using Bi Cubic Spline INTREPID needs to know the orientation of the acquisition lines If you are gridding a field fr
6. Output File Options Output Grid E Testing Processing_Jobs Wijns_Chris_FTG_Tensor_Gridding grav Akjoujti0_Tensor_TC 100_ftp_i ers Sands 1 Banaj iy Band Name ferd Data Options Null value 399999 0 Product ea ti DataType Tensor z Rotation oo Grid Dimensions centroids Origin TL Bottom Right Extents Cells Cellsze x y Reset Extents oo E o ES E E E Output File Options Data Options Library Help Top Output grid Use this text box or browse button to enter the name and path of the output grid See Specifying input and output files Bands Use this spin box to specify the number of bands for the output dataset Band For datasets with more than one band Specify the number of the band that you want this gridding operation to create Band Name Set the output grid band name It defaults to the input Data field name Null Value Set the value to be used to represent a null value in the output grid DataType Use this drop down list to specify the precision of the grid that you are creating See Data Types in INTREPID datasets in INTREPID database file and data structures R05 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 44 Library Help Top lt 4 Back gt Product Use this drop down list to specify the data product that you want to grid If you have specified a scalar field with no gradient enhancement INTREPID disables this li
7. Projection TMAMGS4 Yj Band 1 4 Rotation 00 4 Cell Assignmey 4 duct iX E Grid Grid Control Detautt X E t Laplace Iterations 2 I Edit Origin TL Bottom Right Extents Cells Cell size I x y eset Extertt HY Fill Holes Yes Se Edge Clipping Extrapolation limits MSE Output Grid Output Grid output ers x TEE 100 4 Y E a ELF m BN Cell Size 2 ax OO int Bands 1 aput Vector Data L output Grid int Band 1 Sr DataType IEEE4ByteReal iin Rotation 0 0 4 B Process is valid Data display panels Apply button The following table describes the screen elements Element Purpose Title bar Shows the name of the tool Menu bar Enables you to specify input datasets output datesets job files and to view on line help Toolbar Buttons for specifying input and output datasets as well as units of measurement for the gridding parameters Task specifications tree A list of current set of specifications for the process and files involved To browse the tree use the and buttons to expand and contract the sections Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 13 Library Help Top lt 4 Back gt Element Purpose Available filters list A list of filters available You can select filters from this list Process properties tabs Properties of the current
8. Tensor Interpolation using SLERP A recent invention of Intrepid is to extend the nearest neighbour technique when you are wanting to grid a Full tensor Data field The Spherical Linear interpolation of the rotations quaternions part of the signal is automatically invoked at this stage The Eigenvalues of the tensor are interpolated using the above Nearest neighbour methods for the current triangle In this way an estimate of the curvature gradients of the Potential field can be made smoothly at any point in the near distance to actual observations As this constitutes a major extension to the concept of gradient enhanced gridding the ability to grid to a finer cell size is also present Studies show that instead of the normal 4 cells between flight lines up to 8 cells can be supported without significant aliasing The testing with the Full Magnetic tensor has not been as extensive as with the Full Gravity gradient tensor Gridding Method Bi Cubic Spline Parent topic Gridding Method tab Library Help Top This section is for line dataset gridding only You can produce grids from line dataset fields using this method which is sometimes called fast grid Note The jGridding tool is able to use tiling with this method Also note with lines at an angle it is normal to produce a rotated grid with either rows or columns in the same orientation as the acquisition lines Input Subset Preprocessing Gridding Method
9. Curvature smoothing Save Coarse Grids Good idea to have a look at these to confirm you can see the longer wavelengths Weight Type The normal option here is Unity This means give each point observation equal weighting during the gridding process The other options are Magnitude give more weighting to the observation with the largest positive value eg Depth and Square Root give a weighting to the Square Root of the magnitude of the signal during 3 point interpolations 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 36 Library Help Top lt 4 Back gt Grid Refinement tab Parent topic Gridding T22a Library Help Top After the initial gridding process INTREPID can perform LaPlace convolution and Minimum Curvature grid refinement then restore interpolated grid cells to null as required If you are refining an existing grid INTREPID can perform LaPlace convolution and Minimum Curvature Smoothing refinement The Minimum Curvature process will not use the honour originals method in this case since no original data is available lt gt Specify grid refinement processes in the Grid Refinement tab Input Subset PreProcessing Gridding Method Grid Refinement output Gria 7 Laplace Iterations l 2 a Setting Grid Nulis V Minimum Curvature terations 100 Internal V Fill Holes i Y komore Edges Extrapolation limits Max Residual 00 IV Save Curvat
10. Grid Refinement Output Grid Extrapolation Lint 5 Cell Assignment IV Save Original Data Points OriginatPoints oR H Gridding Method Bicubic_Spine gt I Save Triangles Min Scan Distance 0 0 Max Scan Distance 2000 0 Spline Type Bicubic ha IV Spline Gradient Signal Noise Blending Spline Gradient Noise Level 0 01 While using this method of calculating values for interpolated cells INTREPID creates a located line structure that is closely related to the columns and rows of the grid being created There are three stages of gridding with this method 1 Pass along acquisition lines INTREPID uses spline curves along the acquisition lines to calculate values that will correspond to all grid cells 2 Pass across acquisition lines In the second pass INTREPID examines each column or row of the located line structure perpendicular to the acquisition line direction It notes the values obtained in the first pass nodes and uses them to calculate a spline curve perpendicular to the acquisition line direction It uses the spline curve to calculate values in between the traverse lines The following diagram illustrates the process 3 Box filtering INTREPID passes through the grid using the Box Filter method See Gridding Method Box Filter and creates values for any remaining blank cells 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 30 Library Help Top lt 4 Back gt Bi Cub
11. Help Top 4 Back gt Only keep an interpolated cell if the minimum number of quadrants were populated with original data default is 0 e Minimum Within Only keep an interpolated cell if the minimum number of original data cells are within the extrapolate limit default is 1 Quadrant Extension Make quadrants larger so that they overlap defaults is 0 Example job file syntax INTREPID_QUADRANT_EXTENSION 4 INTREPID_MINIMUM_QUADRANTS 2 INTREPID_MINIMUM_WITHIN 8 Process Begin Name GriddingPro Parameters Begin Input_Datasets_Begin Input_Dataset_1 Begin Input_Daataset dataset DIR Input_X lon Input_Y lat Output Grid tab Parent topic Gridding T22a Library Help Top The Output tab has controls for specifying the output dataset its content datum and projection rotation alignment and constraints In this section Output grid tab Overview of controls e Producing a rotated grid e Note Calculation of the row and column limits Specifying grid alignment Specifying the cell size e Note Calculation of the row and column limits 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 43 Library Help Top 4 Back gt Output grid tab Overview of controls Parent topic Output Grid tab This section gives an overview of the controls in the Output grid tab Input PreProcessing ene Grid Refinement Output Grid
12. reference in INTREPID spectral domain operations reference R14 East horizontal Horizontal derivative in the X direction See Generalised horizontal gradient derivative filter reference in INTREPID spectral domain operations reference R14 North horizontal Horizontal derivative in the Y direction See Generalised horizontal gradient derivative filter reference in INTREPID spectral domain operations reference R14 Vertical gradient Vertical derivative filter including fractional vertical derivative reference in INTREPID spectral domain operations reference R14 Enhanced signal Use this option if you are gridding a scalar field with gradient enhancement See Gridding of potential field data with observed gradients This option is not available if you specify only a vector field of components or gradients as the main data for gridding Calculate diurnal This is experimental beta only Transverse gradient Transverse gradient is the Across gradient component Longitude gradient Tilt angle phase map Longitudinal gradient is the Along gradient component nothing to do with geodetic longitudes If you select Tilt angle INTREPID uses the measured gradients to compute atan dZ total_horizontal_derivative It is similar to the analytic signal except it has the character of the phase of the signal It varies from 90 to 90 degrees See also Gridding sca
13. Gridding Method Grid Refinement Output Gria Extrapolation Limit 5 Cell Assignment a Save Original Data Points OriginaPoints DR E Gridding Method Box Fiter gt I Save Triangles Iterations aS The Box Filter assumes that the original data points are at the cell centroids It does not take account of the actual position of data points within the cell 1 e it has no honour original points process and therefor may not be as accurate as other methods Box Filter as a finishing process for other methods If you use Nearest Neighbours or one of the Spline initial gridding methods INTREPID uses the Box Filter after the process to fill any remaining gaps in the grid Box Filter parameters Box iterations You can use this text box to specify the maximum number of Box filter iterations you want INTREPID to perform before moving to the image refinement stage You do not need to specify Box Iterations if Box Filter is operating only as a final stage of another initial gridding method 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 34 Library Help Top lt 4 Back gt Gridding Method Variable density Parent topic Gridding Method tab Gridding Method Variable _Density Y Reduction Factors E4 v Coarse Iterations 10 Weight Type Unity v O Save Coarse Grids This method was designed especially for gravity data acquired at variable sampling densities
14. Properties E Testing Processing_Jobs Avaanna tilliarsuk Avaanna_DB DIR xrield fx v Datum wese4 Projection NUTM22 Y Field y v Datum wese4 Projection NUTM22 Data Emag x Advanced Scalar J7 Acquisition lines identified by LineType Field gt EBE gt Searing 90 0 Calculate lE M useosbsetorthe dots i acaiton ines ered Nominal bea Bearing 90 0 Calculate Heading Correction Add Remove Use these buttons to add or remove datasets from the Input dataset list See Specifying input and output files Properties Choose Properties to view information about the selected input dataset see Specifying several input datasets INTREPID displays the same information as the Project Manager shows See Dataset preview and information display in INTREPID Project Manager T02 Input dataset The Input dataset list shows the input datasets currently loaded for gridding You can select a dataset to view its information and select options for it See Specifying several input datasets X Field Y Field These drop down lists show the selected geolocation fields of the selected input dataset INTREPID uses the dataset X and Y aliases to make default selections You can choose different geolocation fields from the lists See Specifying several input datasets Data This drop down list shows the data field selected for gridding in the selected input dataset You can select a different field from
15. Select the dataset for gridding 2 Choose Gridding from the Grid menu in the Project Manager or use the command jgridding exe INTREPID displays the Gridding Main window Intrepid Gridding DER Input PreProcessing Gridding Method Grid Refinement Output Grid Input Dataset X Field Unavailable Datum Projection Y Field Unavailable Y Datum Projection Data Unavailable v Input Vector Data Output Grid HR Must have at least 1 Input Datasets 3 Ifyou have a task specification file load it using Load Options from the File menu See Specifying input and output files below for detailed instructions If all of the specifications are correct in this file go to step 10 If you want to modify any settings carry out the following steps as required 4 Choose the input datasets See Specifying input and output files and Input tab 5 Specify the data field for gridding and the geolocation fields See Input tab for general information about this step Gridding vector data Gridding tensor data Gridding of potential field data with observed gradients 6 Ifyou are producing the grid from line data ensure that INTREPID can adequately identify the acquisition lines See Input tab Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 4 Library Help Top Library Help Top lt 4 Back gt 7 Ifyou are producing a grid from a line o
16. algorithm Brigg s formulation is a first order finite difference approximation of La Place condition 13 point kernel This went to considerable trouble to remove any observed horizontal gradient components This traditional formulation is revisited and redone as a second order finite difference approximation 25 point kernel Provision for observed gradients has also been made Variable Density gridding This alternative method also allows for observed gradients No implementation supporting observed gradients is available as yet 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 12 Library Help Top lt 4 Back gt The Gridding window Parent topic In this section Gridding een T22a Gridding window diagram Changing display panel size File menu options e Toolbar e Degrees display style Gridding window diagram Parent topic Here is a diagram of the Gridding window The table below the diagram has more The Gridding information about the window elements window Title bar i ee Process properties tabs a Intrepid Gridding loj x Menu bar eae am afaj os 7 a Process GriddingPro Input Subset PreProcessing Gridding Method Grid Refinement Output Grid Toolbar g E P roa Deve owpteriapamees O o S Sl oleh aie Yeighbour Datumfacoss x Bands i F DetaTypesEEE ByteReal E Task specifications tree Panel size adjustments int Extrapolation Limit
17. between traverse lines or the gap between points of a point dataset You need to specify appropriate cell extrapolation limits for filling these gaps The image refinement processes also require an edge region containing data around the whole grid See Grid Refinement tab for details The data in the edge region around the outside of the grid may be discarded after the image refinement processes This process is called Clipping INTREPID interpolates values for all cells within regions fully enclosed by but outside the edge regions The Masking process deletes sets to null these regions if required Masking needs to know the extent of the edge regions See Setting grid nulls for details gt gt To specify the cell extrapolation limit Enter the limit number of cells away from an original data point into the Extrapolate Cell parameter You should normally use an extrapolate cell value of at least 2 The default value is 2 Cell Assignment Use this to specify the assignment strategy of observations that fall into the same initial grid cell This applies only to grids that are created not reprocessed The options are e Nearest Pick the nearest observation to the cell centroid e First Use the first observation encountered from the database e Last Use the last observation encountered from the database Average Take a running average of all observations in the cell Count Grid up the count of the number of observation
18. coarse grid search radius Max scan distance should default to something very large in order to effectively scan the entire area It is in the same units as the X and Y coordinates Q I want to grid the tie lines as well as the traverse lines How do I do that Use the Nearest Neighbours option if you want to grid all the lines If you have a Linetype field defined re number it to 2 for all lines then grid Another way is to comment out the Linetype alias in the isi file then grid The Nominal Bearing entry will then control what lines get gridded If you leave it blank all lines get gridded Bi splining won t grid all the lines because it ignores lines gt 22 from the required nominal bearing Q How can I change the null value in an INTREPID grid Edit the grid using the Spreadsheet Editor and replace the nulls with the new value Then edit the grid header file and change Nul1Cellvalue to the new value 2012 Intrepid Geophysics 4 Back gt
19. e Toolbar e Output Grid tab Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 16 Library Help Top lt 4 Back gt Aliases Parent topic If possible INTREPID identifies the X Y and line or point type fields from the Specifying dataset aliases Use the following aliases to identify appropriate fields input and omnis Alias Field X East West geographic location coordinate Y North South geographic location coordinate LineType_ Line type PointType Point quality See Vector dataset field aliases in INTREPID database file and data structures R05 for more information about aliases Input tab Parent topic The Input tab has controls for specifying input datasets and selecting fields to use in Gridding the gridding T22a In this section Input tab Overview of controls Specifying several input datasets Identifying acquisition lines e Point quality e Nominal Bearing See also Specifying input and output files Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 17 Library Help Top 4 Back gt Input tab Overview of controls Parent topic Input tab Library Help Top This section gives an overview of the controls in the Input tab Input PreProcessing Gridding Method Grid Refinement Output Grid Input Dataset Add Remove
20. gt INTREPID User Manual Gridding T22a 49 Library Help Top lt 4 Back gt Sample Gridding task specification job file Here is an example of a Gridding task Process Begin Name GriddingPro Parameters Begin Grid_Refinement Begin Fill_Holes yes Edge_Clipping Extrapolation_limits Laplace_Iterations 2 Smoothing_Iterations 2 Curvature_Grid QualityCurve ers Minimum _ Curvature Begin Iterations 100 Max_Residual 0 0 Tension 0 0 Relaxation_Factor 1 375 Kernel_Size 25 Honour_Original_Data 1 Minimum _ Curvature End Grid_Refinement End Output_Grid Begin Output_Grid output ers Datum NAD83 Projection NUTM17 Cell_Size_X 75 000000 Cell_Size_Y 75 000000 Band 1 Bands 1 DataType IEEE4ByteReal Rotation 0 0 Origin_X 451950 000000 Origin_Y 5395575 000000 Columns 481 Rows 301 Output_Grid End PreProcessing Begin Name Naudy Maximum_Anomaly Width 100 0 Tolerance 0 0001 Use_Corrected_Data yes PreProcessing End Gridding_Method Begin Extrapolation_Limit 5 Cell_Assignment Closest Save_Triangles no Name Variable _ Density Coarse_Iterations 10 Reduction_Factors 5 4 3 Coarse_Grid coarse_grid ers Orig_Pts_Dataset OriginalPoints DIR Gridding_Method End Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 50 Library Help Top lt 4 Back gt Vector_Subset Begin Name Rectangle BottomLeft_X 0 0 BottomLeft_Y 0 0 TopRight_
21. over the region you wish to create a gridded representation of the field The basic intent of the method is to estimate various wavelength contents optimimally and to combine them into one final grid that has the best assemblage of observed wavelengths from the datasets provided To illustrate the above discussion further take the case of regional gravity data being collected on a regular grid at say 4 km spacings Added to that you may also have observations taken along roads that criss cross the area Added to that again you may also have some small areas where detailed gravity observations have been carried out on a grid at say 200m spacings The method is implemented using a multi grid approach Working back from the required final cell size a series of 2 or 3 extra coarser grids are produced using the Nearest neighbour technology These coarse grids are designed to properly capture the longer wavelength data at an appropriate cell size eg for 4 km data a 1 km cell size would not be aliased and properly represents this aspect of the signal The final cell size might well be 50m with the aim of capturing the higher frequency shorter wavelength field information from the 200m data To progress down to this finer cell size a resampling from the coarsest grid to the next intermediate grid is made lets say 200m cell size This intermediate grid is then immediately weeded around those cells that fall near an observation of gr
22. the list See Specifying several input datasets Advanced Use Advanced to specify the gradient fields for gradient enhanced gridding See Gridding of potential field data with observed gradients The selected data type appears immediately to the right of the Advanced button as a hint to the user The three possible types are illustrated below 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 18 Library Help Top Library Help Top 4 Back gt Scalar a E ae Mic Poo Datum SAD69 Projection SUTM24 Data SRTM_Terain O Z Acquisition inesidentifiedby_ LineType Fied linetype Bearing 90 0 Caleulate 7 Heating Correction Vector X Field x v Datum san69 Projection SUTM24 ge TE Projection SUTM24 Data TC_Components anea V Acquisition lines identifiedby LineType Field x LineType Bearing 90 0 Calculate 7 Heading Correction Tensor Coord System xiedfes S Datum SADE Projection SUTM24 vrdfy ts sSOSSS ef Datu SADE Projection SUTM24 Data TC267_Gradents 0000 od Tensor Feld END IV Acquisition lines identified by flinetype Field linetype Bearing 90 0 Calculate I Heading Correction For multiband datasets the Advanced button changes to a band selector with the total number of bands available shown to the right Multiband X Field x gt Datum GDAS4 Projection MGASS Y Field y T Datum cDa94 Projection MGA5
23. window in data points using the Window Size data points text box See Convolution preprocessing for an explanation This is a filter for smoothing the data For each point INTREPID will compare each data value with neighbouring values along the line If there are sudden changes INTREPID will adjust the current data value to make the changes smooth You need to specify the following Window Size data points Use this to specify the number of data points to be compared around the point being adjusted For example if you set the window to 4 INTREPID will examine two points on each side of the current point to calculate any adjustment The default value of this parameter is 2 Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Gridding T22a 23 4 Back gt Naudy preprocessing Parent topic Preprocessing tab Input Subset PreProcessing Gridding Method Grid Refinement Output Grid PreProcessing Naudy v Naudy Maximum Anomaly Width 100 0 Tolerance i 0 0001 C Reject Data If you have chosen the Naudy filter specify The filter wavelength in data points using the Maximum Anomaly Width text box The filter tolerance in data units using the Tolerance text box Whether you want to produce the grid from the corrected data or from the data rejected by the filter i e the noise See Naudy preprocessing for an explanation This filte
24. 5 Data BFieid v Band p H Advanced Bands 40 d isition lines identified by linet ype Field x IGS_LType x Bearing 90 0 Calculate i Heading Correction Acquisition lines identified by check box Line datasets only Use this check box to specify whether you want to distinguish acquisition lines from other lines in the selected dataset See Identifying acquisition lines and Specifying several input datasets 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 19 Library Help Top 4 Back gt Acquisition lines identified by drop down list Line datasets only Use this drop down list to select the method of identifying acquisition lines in the selected dataset See Identifying acquisition lines and Specifying several input datasets LineType Field Line datasets only acquisition lines identified by line type When this option is chosen a list box appears to the right allowing the user to choose the appropriate Linetype field name See Acquisition lines identified by a line type field Nominal bearing Line datasets only acquisition lines identifid by nominal bearing Nominal bearing for acqusition lines See Acquisition lines identified by Nominal Bearing and Nominal Bearing Calculate Choose Calculate to automatically calculate the nominal bearing of the dataset See Acquisition lines identified by Nominal Bearing and Nominal Bearing Heading correction S
25. INTREPID User Manual Gridding T22a 1 Library Help Top lt 4 Back gt Gridding T22a Top This chapter refers to the current Gridding tool Gridding For information about the old gridding tool see Old Gridding T22 You can use INTREPID Gridding to convert point and line data to a grid suitable for image processing and contouring enhancing it using local gradients of the data field The tool adapts to the datatype of the field you have chosen to grid Scalar Vector Tensor setting more appropriate defaults as you progress INTREPID divides the region being processed into a grid of square cells Each grid cell will contain a value derived from an original data point an original data cell or interpolated from neighbouring cells or nearby points an interpolated cell The Pro version of this tool also supports multi dataset gridding allowing you to choose a great many individual survey datasets and dynamically create a grid from the selected channel in each dataset The current best effort exceeds 7000 datasets INTREPID has two other special grid dataset processing tools The Grid Operations tool can resample the grid change the cell size and rotate the grid See Grid Operations T25 for information about this tool The INTREPID GridMerge tool can combine overlapping or adjacent grid datasets correcting for differences between them See GridMerge merging multiple grids T24 for a full description In this cha
26. REPID uses a masking process to make the grid conform to these requirements It sets to null all interpolated cells that are too far from an original data cell INTREPID can use the value of the Extrapolate Cell parameter as the limit for retaining or removing interpolated cells For example if Extrapolate Cell 2 then it can set to null all interpolated cells that are more than 2 cells away from an original data cell Internal fill holes If you want INTREPID to fill all holes check this check box INTREPID fills all holes regardless of The value of Extrapolate Cell e Your selected Setting grid nulls option for Edges Edges Use this drop down list to specify masking for the edges of the grid Setting Descriptions Original data limits INTREPID sets to null all extrapolated edge cells non original data cells Extrapolation limits INTREPID sets to null all extrapolated edge cells that are further from an original data cell than the Extrapolate Cell value Strict Extrapolate cells A new more robust version of Extrapolation limits which uses a moving window and is sensitive to internal holes also better for random point data of variable spacing Three further tuning options are available for this method in batch mode see below Strict Extrapolate Cells tuning options batch only Minimum Quadrants 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 42 Library
27. X 0 TopRight_Y 0 Rotation 0 0 Vector_Subset End Parameters End Process End Syntax table ooo This table contains the following sections e A complete task specification file outline with all possible statements and blocks including File specifications Parameters The table wil be available in the next edition of this manual Using task specification files You can store sets of file specifications and parameter settings for Gridding in task specification job files gt gt To create a task specification file with the Gridding 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 specification job files R06 gt gt To use a task specification file in an interactive Gridding 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 Gridding task Using Project Manager This method enables you to use the extended task specification language available to the Project Manager For instructions see Executing batch mod
28. alar grids or a full tensor grid Product Description X Y Z XY YZ ZX Individual tensor components Determinant I1 First invariant of the tensor Maximum Middle Minimum Eigenvalue Trace Txx Tyy Tzz Second invariant I2 Ratio see Peterson Strike atan I2 11 Horizontal gradient amplitude direction Curvature gradient amplitude direction Grid This is the default and it means create a Fully interpolated 6 band BIL Ermapper grid with each component stacked band by band Note geosoft does not support the notion of multi band geophysical grids so do not use a grd output grid extension The most important innovation here is the use of the patented SLERP or Spherical Linear interpolation method to allow a Full tensor interpolation This is used for all of the above options and the calculation from the interpolated tensor is done at the point of populating the cell with an output value See also Gridding scalar data Gridding vector data lt Gridding of potential field data with observed gradients Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 9 Library Help Top lt 4 Back gt Gridding of potential field data with observed gradients Parent topic INTREPID can produce superior results if you supplement a scalar input field with Using the observed gradients Gridding tool Specifying gradients as a
29. and the x y checkbox to specify the size of one grid cell in oo Grid the distance units of the dataset ta Setting an appropriate cell size is a balance between having a fine mesh grid and having gaps or excessive interpolation between cells which may lead to inaccuracies If you are gridding from a line dataset we recommend a cell size not greater than one quarter to one fifth of the line spacing If you have a smaller cell size than recommended we suggest that you increase the cell extrapolation limit See Extrapolation limit for details Note If your dataset is geodetic latitude and longitude you need to specify the grid cell size in degrees Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 47 Library Help Top Apply Parent topic Gridding T22a Library Help Top lt 4 Back gt Note Calculation of the row and column limits The row and column limits of the grid are lists of the locations of the outermost cells in each row and column which are to contain data In this discussion we will use the following notation EC value of the Extrapolate Cell parameter Lo cell position of the outermost original data cell at the current end of the current row or column Le cell position EC cells further out than Lg for the current end of the current row or column Lp the set of Lp cell positions for the current end of the EC rows or columns b
30. avity opening up the gridded representaion of the field for further interpolation and local estimation Finally in the scenario from above a jump to the 50 m cell size is made Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 35 Library Help Top Library Help Top 4 Back gt Notes about implementation detail 1 Low prime number ratios between cell sizes are used to minimise resampling artifacts You are asked to choose from a limited set of factors that range through combinations of 2 3 4 5 7 and 11 2 Weeding goes out around any observation a distance of 2 cells sizes at each stage 3 At least 10 iterations of Minimum Curvature are applied to the coarse grids to ensure a good representation of the smoothed long wave content is created and can be handed on to the next stage 4 Persistence of longer wavelength features can be clearly seen in the output grids following application of this method 5 The method was devised at Geoscience Australia by several workers including Alice Murray in an effort to create a best possible gravity grid from extremely irregularly sampled field data Pass list Reduction factor This is the list of prime number factors to reduce from a coarse cell size to the final cell size using a multi grid approach Cell Size Final cell size required Coarse Iterations You can influence the number of iterations of coarse MIN
31. cell centroid when calculating the weight influence of the cell in an adjustment of a neighbouring cell This can improve the accuracy of the image refinement process An original data point can have up to 128 x 128 different positions in a cell If you are using the Gridding tool to enhance an existing grid original data is not available and INTREPID will automatically turn Honour Original Data off The Honour Original Data method has two variants 1 cell and 2 cell See the section immediately following for an explanation Note The honour original data process described here uses the same information but is otherwise independent of the honour original data process used in Nearest Neighbours initial gridding See Gridding Method Nearest Neighbours Honour Original Data 1 or 2 cell Choose the option button according to your requirements The default option is 2 cell For 1 cell Honour Original Data INTREPID simply calculates the weight influence of each original data cell on neighbouring cells based on the location of the original data point rather than the cell centroid as explained above For 2 cell Honour Original Data for each original data cell INTREPID 1 Locates the quadrant of the original data cell in which the original data point lies 2 Treats the 3 cells surrounding this quadrant as original data cells 3 Locates the nearest original data points to the respective centroids of the 3 cells 4 For each of the 3 cel
32. d of the additional data points created between the acquisition lines the additional trend points gt gt To save the additional trend points Assign a value to the system parameter INTREPID_TREND_POINTS before processing INTREPID will save the additional trend points as a point dataset called trend See INTREPID system parameters and install cfg R07 for further information about system parameters in INTREPID Process reports for the Trend Spline method You can inspect a report of the aspect ratio between line spacing and cell size during the gridding process Under Unix this appears in the background window Under Windows it is written to an ntout report file See Diagnostic reporting options in Configuring and using INTREPID R04 for more information 3 in Z units for example nT 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 33 Library Help Top 4 Back gt Gridding Method Box Filter Parent topic Gridding Method tab Library Help Top You can produce grids from line and point dataset fields using this method The Box filter progressively examines each empty cell in the grid in relation to its immediate neighbours and calculates a value for it based on an average value of its neighbours The Box Filter process repeats until all cells have a value or until it has completed the maximum number of iterations you have specified Input Subset PreProcessing
33. dealing with vector components of the potential field this convention must be applied Assuming a moving platform for the acquisition vehicle such as an aeroplane The local Y positive or length component is tail to tip positive The cross component is left to right positive The vertical component is upwards positive Storage of gradients in the source dataset The gridding algorithm accepts any or all of these vector gradients Before gridding convert the differences between readings to nT m Divide the difference by the distance between instruments The local heading of the observation is also computed from the X Y data and the components are stored with each scalar field observation as vector components in the E N amp Vertical projection system That is the observations are stored in a normalized coordinate frame for internal use Opportunities for using this extra gradient data Direct gridding of observed analytical signal OLY SL 8T DOG Direct gridding of observed total horizontal gradient i e ST 8T A Enhanced potential TMI Gravity field grid honouring observed gradients see Enhanced potential field gridding further notes For TMI calculation of a short wavelength diurnal variation Akima splines These are able to take an observed gradient along the spline direction The line direction gradient component is calculated for each observation point as required Minimum Curvature
34. ding tool to enhance an existing grid the grid will have no link with its original data and therefore INTREPID cannot use any honour originals method See below for additional explanation of the honour originals process At the end of the Minimum Curvature process INTREPID can perform several further passes through the grid where it adjusts original data cells values in the same way as it has been adjusting interpolated cells This process is called smoothing and has the effect of further smoothing the grid near original data cells If you are using the Gridding tool to enhance an existing grid INTREPID will only perform the Minimum Curvature process in Smoothing mode since the original data can not be distinguished Iterations Use this spinner to specify the maximum number of times that INTREPID may scan through the grid number of iterations during the minimum curvature process Kernel size Use this drop down list to specify the kernel size for the minimum curvature process Maximum Residual Each time INTREPID scans the grid in its attempt to smooth the grid it may cause a change in the value of each interpolated cell As it completes each progressive scan the change in each cell becomes smaller the interpolated values are becoming settled Use this text box to specify the stage at which you consider that the interpolated values are sufficiently settled subsequent residual changes will be ignored Specify the Maximu
35. directions If you set these values INTREPID automatically adjusts Bottom Right and Extents Cell size Use these spin boxes to specify the size in distance units of the cells in the grid in the X and Y directions If you set these values INTREPID automatically adjusts Bottom Right Extents and number of Cells You can specify equal size in both directions using the x y checkbox See Specifying the cell size for more information If you click and type the required cell size into these boxes rather than use the spinners then you must hit return before INTREPID will update the Bottom Right Extents and number of Cells X y Use this check box to specify whether cells are of the same size in both directions If you check this box INTREPID uses the X Cell size for both cell dimensions 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 45 Library Help Top lt 4 Back gt Reset extents Choose Reset extents to automatically recalculate the default extents for the output grid Producing a rotated grid Parent topic You may be gridding a field from a line dataset with oblique acquisition lines that al Grid do not lie North South or East West The survey may have been created like this a for example so that the data is perpendicular to the strike of a feature of interest You may want to produce a rotated grid from oblique data with its rows or columns in the direction of the acquisitio
36. e by the relaxation factor The default value of the relaxation factor is 1 375 Where Zo 1s the value in the cell being processed before the Minimum Curvature adjustment Za is the adjusted value in the cell after the Minimum Curvature process has been applied R is the relaxation factor Z is the new value in the cell being processed after the minimum curvature process and relaxation factor adjustment have been applied If Zp does not contain original data then Z Z4 Zo x R Zo INTREPID will repeat the process until it has completed the number of iterations you specify in the Maximum Iterations text box or the maximum residual change for all cells is less than the value you specified in the Maximum Residual text box whichever occurs first 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 39 Library Help Top Library Help Top 4 Back gt INTREPID normally uses a kernel of cells immediately surrounding the target cell as comparison values in the Minimum Curvature process as shown below The Minimum Curvature process can use an honour original data system if required If you choose this method INTREPID allows for the actual position of the original data point in an original data cell rather than the cell centroid when calculating the weight influence of the cell in an adjustment of a neighbouring cell If you are using the Grid
37. e tasks with the Project Manager in INTREPID Old Project Manager T01 For information about the Project Manager task specification language extensions see Special Project Manager batch task operations in INTREPID task specification job files R06 Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 51 Library Help Top 4 Back gt Using Gridding directly Type the command jgridding 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 surv329 job in the current directory you would use the command jgridding exe batch surv329 job Frequently asked questions Parent topic Gridding T22a Library Help Top Q Why doesn t Bispline gridding appear to fill the grid properly on a dataset with angled lines Splining only works in the NS or EW direction It depends on the bearing entered If you enter a bearing of 90 it will spline NS for lines which have a bearing within 70 110 420 from 90 or if you enter 0 it will spline EW for lines bearing 340 20 If you enter 45 you will need to select Rotate dataset or else it will try and spline NS as if lines were bearing 90 and not find many node points outputting a generally blank grid Q What should I make the coarse grid Maximum scan distance for variable density gridding The
38. ed the input dataset see Specifying input and output files and Specifying several input datasets Specify the scalar field that you are gridding Use the Data drop down list in the Input tab see Input tab Choose Advanced INTREPID displays the Input gradients dialog box Input Data x Single Field Data iate wj Date Vector Field Group M Across G_acc_x m M Along G_acc_y ad M Vertical G_acc_z Select Vector Field Group Check the Across Along Vertical check boxes according to the gradient fields you have available For each gradient field select a field from the corresponding drop down list Choose Close In the Output grid tab from the Product drop down list select Enhanced Signal Product Enhanced Signal ha The minimum you must specify is one gradient or component of the field The Bi Spline method is choosen by default as the appropriate gridding method in this case It is recommended you not use any Grid refinements such as Laplace or MINQ as these tend to negate the subtle contributions made by the observed gradients 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 11 Library Help Top 4 Back gt Enhanced potential field gridding further notes Parent topic Using the Gridding tool Library Help Top Sign convention for gradients from an aircraft There is a local coordinate convention associated with acquisition Since we are
39. ee Acquisition lines identified by Nominal Bearing and Nominal Bearing Specifying several input datasets Parent topic Input tab INTREPID can combine several datasets in one grid The Input dataset list shows the currently loaded input datasets The highlighted dataset is the currently selected dataset INTREPID displays information about this dataset in the Gridding window Input Tab You can set input options for this dataset To select a different input dataset click it so that it is highlighted Identifying acquisition lines Parent topic Input tab Library Help Top This section is for line dataset gridding only It is normal practice to use only acquisition lines in the gridding process for line data Acquisition lines identified by a line type field If there is a LineType alias or if you specify a line type field in response to a prompt INTREPID will use it to automatically exclude non acquisition line data processing types 2 and 3 only See Traverse line numbers and types in INTREPID database file and data structures R05 for a complete list of traverse line types and numbers If your dataset does not have a line type field but does have line numbers from which you can derive a line type field you can use the INTREPID Spreadsheet Editor facility to create it See Create new field example Line Type field in Spreadsheet Editor T15 for details about creating line type fields 2012 Intrepid Geophysics 4
40. efore and EC rows columns after the current row column Max Lg the outermost Lg position in the Lg set L row or column limit finally recorded INTREPID calculates the row and column limits as follows For the left hand end of each row INTREPID 1 Locates the leftmost original data cell Lo Locates the cell EC cells further left than Lo Lg HEC Finds the leftmost cell of the set Ly Max Lg 2 3 Locates the Lx positions for the previous EC rows and the next EC rows Lg 4 5 Records the X coordinate of Max Lp 9 as the X coordinate of the left hand row limit for the current row X coordinate of L The Y coordinate is of course the row number INTREPID performs this process correspondingly for the right end of each row and for each end of the columns The overall effect of this process is to Produce a square ended effect for groups of rows and columns and Fill out rows columns with inadequate original data cells to a common grid edge When you choose Apply INTREPID carries out the Gridding process that you have specified 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 48 Library Help Top 4 Back gt Task specification job files in Gridding Parent topic Gridding T22a This section gives an overview example and describes the syntax of Gridding task specification files A Gridding task specification
41. ent _ East Horizontal Gradient North Horizontal Gradient Vertical Gradient Enhanced Signal Transverse Gradient Longitude Gradient Tit Angle Phase Map bd You can choose the following derived grid products The illustration shows the Product drop down list in the Output grid tab see Output Grid tab The default product is an Enhanced Signal grid The tool will automatically choose this option if you use the Advanced button to add an Across gradient field to addition to the scalar signal field you have already chosen To produce directly any of the other grid products listed below you must add via the Advanced button the appropriate sets of observed gradient fields With the object oriented data types now available in INTREPID you can also use the Single Field intelligent to add all vector components via the one field 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Gridding T22a 6 lt 4 Back gt The option of having each gradient as a separate field in your database is provided to preserve Canadian thinking even though users may lose track of what processes have been applied to each component in prior levelling and other data conditioning Product Details Analytic signal Analytic signal filter reference in INTREPID spectral domain operations reference R14 Total horizontal gradient Total horizontal derivative filter
42. ic Spline parameters Minimum Maximum Scan Distance When interpolating a value for a group of cells during the second pass of the Bi Cubic Spline process INTREPID searches in both directions for nodes so that it can calculate a spline curve It requires two nodes on each side of the cells This parameter specifies a distance limit for this search If INTREPID cannot find the nodes within this distance it will not interpolate the cells Specify the Search Radius in distance units in the corresponding text box We recommend a Search Radius larger than twice the line spacing or 10 times the cell size The recommended number of cells from one line to the next is 4 Note If your dataset is geodetic latitude and longitude you need to specify the Search Radius in degrees Nominal Bearing Rotate Line Data Spline Type Spline Gradient Signal Noise Blending Spline Gradient Noise Level Gridding Method Trend Spline Note This method is retired and no longer available Parent topic This section is for line dataset gridding only You can produce grids from line dataset Gridding fields using this method This method is retired and no longer available Sorry but it Method sap was not worth the effort of keeping it going and also with the new intelligent data type fields quite tricky to support For instance how do you define a trend for a tensor field DJF Dec 2007 Trend spline uses Bi Cubic Spline gridding but includes a prelim
43. inary process which examines groups of lines together to find directional trends Using this information in the gridding process can enhance the appearance of anomalies that lie at oblique angles to the traverse lines Input Subset PreProcessing ridding Method Grid Refinement Output Gria Extrapolation Limit g Cell Assignment I Save Original Data Points foriginaPorts OR OOO el Gridding Method Trend_Spline 7 IT Save Triangles Min Scan Distance 0 0 Spline Type Akima zi Max Scan Distance 2000 0 Trend Picker Window Size 100 Min Anomaly i 1 0 Min Search Angle 45 0 IV Save Trend Points Dataset firendSpinePoints DR Note We recommend that you only use this method with surveys that have regularly spaced lines Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 31 Library Help Top Library Help Top lt 4 Back gt The Trend Spline direction finding process involves two basic steps 1 INTREPID examines changes in all directions along groups of lines and calculates a trend direction for each data point the direction in which there is the least change 2 INTREPID uses this data to create sets of additional data points between the acquisition lines After the direction process INTREPID creates the grid using the Bi Cubic Spline method See Gridding Method Bi Cubic Spline The process finds maxima and minima in adjacent lines and associates them
44. ions and a list of the process and files involved expand the task specification tree in the Process panel on the left After Gridding you can carry out a more detailed inspection of the grid using INTREPID Visualisation see Visualisation T26 You can execute Gridding as a batch task using a task specification file that you have previously prepared See Task specification job files in Gridding for details 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Library Help Top Gridding T22a 5 lt 4 Back gt Gridding scalar data Parent topic Using the Gridding tool If you specify a scalar field as the Data field for gridding see Input tab Overview of controls and you do not specify a gradient field INTREPID produces a grid of this data The illustration shows the Product drop down list in the Output grid tab Product fx z See also Gridding vector data Gridding tensor data Gridding of potential field data with observed gradients Gridding vector data Parent topic Using the Gridding tool Library Help Top You can specify a vector field see Compound data types in INTREPID database file and data structures R05 as part of the input for gridding You can specify it either as the Data see Input tab Overview of controls or as the gradient of the data see Gridding of potential field data with observed gradients Product analytic Signal x Total Horizontal Gradi
45. lar data Gridding tensor data Gridding of potential field data with observed gradients Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 7 Library Help Top lt 4 Back gt Gridding tensor data Parent topic Using the Gridding tool Library Help Top You can specify a tensor field see Compound data types in INTREPID database file and data structures R05 as the Data field for gridding see Input tab Overview of controls INTREPID can produce grids of the following products The illustration shows the Product drop down list in the Output grid tab see Output Grid tab To access this functionality you must have created a tensor field in your database either on import or via the dbedit tool Generally it is assumed you would have a normal fully populated tensor though there is some support for what we call the Horizontal tensor as observed by the Falcon system This consists of the Txx Tyy and the Txy components Product z z Maximum Eigenvalue Middle Eigenvalue Minimum Eigenvalue Trace Second Invariant Ratio Strike Horizontal Gradient Amplitur Horizontal Gradient Directio Curvature Gradient Amplitur Curvature Gradient Directio Grid 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 8 Library Help Top Back gt You can choose to produce either a range of one band sc
46. ls uses the value of its chosen data point and its position to calculate the weight influence of the cell for adjusting neighbouring cells Smoothing If you turn on Smoothing after INTREPID has completed the Minimum Curvature process it will perform several further Minimum Curvature passes through the grid During these passes it will adjust original data cell values in the same way as it has been adjusting interpolated cell values This has the effect of further smoothing the grid 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 41 Library Help Top lt 4 Back gt Smoothing Iterations Use this spin box to specify the number of smoothing iterations to perform Save curvature grid Contact our technical support service for information about this parameter Setting grid nulls Parent topic Grid Refinement tab Library Help Top Depending on the density of your original data the cell size and the value of the Extrapolate Cell parameter INTREPID will fill gaps in the grid during the gridding process You may on one hand require a grid with no undefined regions and require the Gridding tool to fill all gaps as best it can by interpolation On the other hand you may Have one or more regions which have no observed data at all and for which interpolated data would be meaningless or e Require that the grid contain only data that is close to original data points INT
47. ly selected Gridding process step Apply button Click this button to run the filtering process Panel size adjustment Use this to change the relative size of the data display area and the lists and properties area Changing display panel size Parent topic The Gridding window Use the panel size control to change the relative size of the data display area and the task control area gt gt To adjust the size of the data display and task specification areas Drag the panel size control up or down OR Click the up and down arrow icons ja to make the data display or task specification area occupy the whole window Click the icons again to restore the display so that both areas are visible File menu options Parent topic The Gridding window Library Help Top See Specifying input and output files for more information File Help Open Input Dataset Specify Output Dataset Load Options Save Options Exit Open Input Dataset Use this option to specify the input vector dataset Specify Output Dataset Use this option to specify the grid name The output grid may be a new or existing grid Load Options If you want to use an existing task specification file to specify the Gridding 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 Gridding process See Task specification job files in G
48. m Residual in the same units as your signal data If you are gridding magnetic data we recommend a value of 0 1nT to produce the best print quality The Minimum Curvature process will stop when Every cell has changed during the last scan by less than the value that you specify the maximum residual change or The maximum iterations have been performed 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 40 Library Help Top Library Help Top 4 Back gt Relaxation factor See above in this section for an explanation of the function of the relaxation factor Task files You can change the value of the relaxation factor if you are using a task specification job file for your gridding process Edit the job file changing the value in the Relaxation_Factor line according to your requirements Example Relaxation_Factor 1 325 See Task specification job files in Gridding for information about batch mode Tension Contact our technical support service for information about this parameter Honour Original Data If you turn off Honour Original Data INTREPID will assume that the original data points are located at the centroids of all original data cells and calculate the same weight influence for the cell in all directions If you turn on Honour Original Data INTREPID will allow for the actual position of the original data point in an original data cell rather than the
49. n lines After producing the grid you can rotate it so that the rows lie East West See Rotating a grid in Grid Operations T25 for instructions If you are gridding an oblique line dataset using the Bi Cubic Spline or Trend Spline method in the gridding process you must produce a rotated grid With the Nearest Neighbours and Box Filter methods producing a rotated grid from an oblique line dataset is not compulsory See Gridding Method tab Specifying grid alignment Parent topic Note This feature is not supported in Intrepid V4 2 3 Output Grid Grid Control Detaut Grid ContralfSame as be Cu Datasets sanders_bouguer ers ia Grid Control Aligned with grid iv C1 Datasets sanders_bouguer ers ai Grid Contraljligned with coordinates Y X 0 0 Yy 0 0 Default Same as another grid Use the text box or browse button to enter the name and path of the control grid See Specifying input and output files Aligned with another grid Use the text box or browse button to enter the name and path of the control grid See Specifying input and output files Aligned with coordinates X Y Specify the coordinates of the alignment point in the X and Y text boxes using distance units of the output grid Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 46 Library Help Top lt 4 Back gt Specifying the cell size Parent topic Use the Cell Size spin boxes
50. ng Method Box Filter Gridding method Variable density This method was designed especially for gravity data acquired at variable sampling densities over the region you wish to create a gridded representation of the field The basic intent of the method is to estimate various wavelength contents optimimally and to combine them into one final grid that has the best assemblage of observed wavelengths from the datasets provided To illustrate the above discussion further take the case of regional gravity data being collected on a regular grid at say 4 km spacings Added to that you may also have observations taken along roads that criss cross the area Added to that again you may also have some small areas where detailed gravity observations have been carried out on a grid at say 200m spacings See Gridding Method Variable density 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 25 Library Help Top lt 4 Back gt Grid initialisation Parent topic The first stage of gridding involves three processes Griddi a Maihod an 1 INTREPID reads the input data If it is a vector dataset INTREPID creates a grid data structure and aligns it with the source dataset 2 INTREPID identifies the grid cells that contain one or more original data points It finds the nearest data point to the cell centroid and assigns its Z value to the cell It also records the exact position of the original da
51. olute If you browse INTREPID displays an Open or Save As 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 In this section Overview of input and output files e Aliases 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 15 Library Help Top lt 4 Back gt Overview of input and output files Parent topic This section is a summary of the input and output files with cross references to the Specifying instructions about them input and output files Input files Input vector dataset e Aliases aliases that this tool uses File menu options e Toolbar Input tab Subsection polygon a many sided polygon that can clip the area to be gridded Input task specification file File menu options e Toolbar Grid for alignment of output grid Specifying grid alignment Output files Intermediate output files Original data points from gridding methods see Gridding Method tab Coarse grids from variable density gridding method see Gridding Method Variable density lt Trend points from trend spline gridding method see Gridding Method Trend Spline e Curvature grid from grid refinement see Grid Refinement tab Output task specification file e File menu options e Toolbar Output grid File menu options
52. om a line dataset using Nearest Neighbours Variable Density or Box Filter you can specify the orientation of the acquisition lines for the purposes of quality control 1 e rejecting lines that have different orientation or to specify rotation for the grid INTREPID compares the Nominal Bearing parameter with acquisition line orientation It uses the parameter for the following purposes Determining the line direction for Bi Cubic Spline and Trend Spline initial gridding See Gridding Method Bi Cubic Spline and Gridding Method Trend Spline below Identifying acquisition lines if there is no line type field See Acquisition lines identified by Nominal Bearing for more information e Acquisition line quality control INTREPID will only process traverse lines whose direction is within 22 of the specified Nominal Bearing This rule applies irrespective of the acquisition line identification method See Identifying acquisition lines Specifying the required angle for a rotated grid if you have acquisition lines that do not lie North South or East West See Producing a rotated grid 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 21 Library Help Top lt 4 Back gt To calculate the Nominal Bearing Set the Acquisition lines identified by to Nominal Bearing Press the Calculate button INTREPID automatically calculates the bearing of the traverse lines in the dataset fo
53. pter How to use this chapter Summary of the gridding process Using the Gridding tool The Gridding window Specifying input and output files e Input tab e Preprocessing tab Gridding Method tab Grid Refinement tab Output Grid tab Apply Task specification job files in Gridding e Frequently asked questions Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 2 Library Help Top 4 Back gt How to use this chapter Parent topic This chapter describes the operation of the Gridding tool You can use the Gridding Gridding both interactively and in INTREPID batch processing mode using INTREPID task T22a specification job files Where needed in this chapter there are separate Interactive and Task files sections Some sections are marked Interactive only or Task files only You can find out how to use the tool and also get background information as follows For instructions on using the tool interactively see Using the Gridding tool For details about task specification job files see Task specification job files in Gridding Summary of the gridding process Parent topic 1 Gridding T22a 10 If you are gridding line or point data you specify the data field for gridding in one or more datasets If you are enhancing an existing grid you specify the grid dataset name and go to step 6 You specify the proce
54. r point dataset specify e Pre processing see Preprocessing tab Gridding method see Gridding Method tab Grid refinement see Grid Refinement tab Output grid see e Output Grid tab for general information Gridding vector data lt Gridding tensor data Gridding of potential field data with observed gradients 8 Choose Apply INTREPID performs the gridding process saves the output dataset and displays the results graphically in the Output Grid panel a Intrepid Gridding gt lo x Fie Help aaj efa 2 Process GriddingPro SE Parameters input Subset Preprocessing Gridding Method Grid Refinement Output Grid Output Grid joutput ers oo Datum aGDss T Bands 1 DataType EEE4ByteRea Z Projection TMAMGS54 Yj Band 1 Rotation 00 fal Product x z Grid Control Detautt x I Edt Origin TL Bottom Right Extents Cols Cell size I xey x al a amal j Y al a P 5 Input Vector Data d Output Grid B Process is valid 9 Ifyou want to record the specifications for this process in a task specification job file so that you can repeat a similar task later use Save Options from the file menu See Specifying input and output files for detailed instructions 10 Ifyou want to repeat the process repeat steps 2 9 varying the parameters and or data files as required 11 To exit Gridding choose Exit from the File menu To view the current set of specificat
55. r reduces noise in your data by detecting sudden changes or spikes that are not characteristic of potential field data You need to specify the following Maximum Anomaly Width data points Use this to specify the wavelength in data points for the Naudy filter The wavelength corresponds to the maximum width of noise anomalies to be removed INTREPID will remove anomalies shorter than the wavelength you specify The default value is 2 Tolerance Use this to specify the filter tolerance in Z units The tolerance corresponds to the minimum amplitude of suspected noise anomalies to be removed INTREPID will remove spikes with a amplitude higher than the tolerance you specify The default value 0 1 corresponds to 0 1nT the current documented accuracy of magnetometers This ensures that INTREPID will only remove noise and not waste time attempting to smooth out the normal fluctuations associated with the precision limits of the instrument Naudy Filter Options Select Use Corrected Data to produce the grid from the Library Help Top corrected data Select Use Rejected Data Noise to produce the grid from data rejected by the filter the noise 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 24 Library Help Top lt 4 Back gt Gridding Method tab Parent topic Gridding T22a Library Help Top Gridding uses a mathematical interpolation and extrapolation process to calc
56. r you and writes the entry into the nominal bearing box Subset tab Parent topic You can specify a region of interest for the Gridding process usinga polygon dataset wa INTREPID will only grid data within the region defined a You can use the Subsection tool to define a polygon See Subsections of datasets T21 for full instructions gt gt To specify a region of interest using a polygon dataset Select the Polygon option on the Subset tab and specify the polygon dataset required see Specifying input and output files Library Help Top 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 22 Library Help Top lt 4 Back gt Preprocessing tab Parent topic You can choose one of the following Gridding T22a e No preprocessing lt A Convolution filter for smoothing the data see Convolution preprocessing e A Naudy filter for noise reduction see Naudy preprocessing Select the process you require from the Preprocessing drop down list on the Preprocessing tab The default process is None Input Subset PreProcessing Griding Method Grid Refinement Output Gria PreProcessing None hed p PreProcessing Convolution preprocessing Parent topic Preprocessing tab Input Subset PreProcessing crigaing Method Grid Refinement Output Grid PreProcessing Convolve Convolve Window Size 2 4 1 Ifyou have selected Convolve specify the size of the convolution
57. ridding for more information Save Options If you want to save the current Gridding file specifications and parameter settings as an task specification file use this menu option to specify the filename and save the file See Task specification job files in Gridding Exit Use this option to exit from the tool 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 14 Library Help Top Toolbar Parent topic The Gridding window 4 Back gt The toolbar has the following buttons aaj afa ol 2 Specify input dataset Specify output dataset Load options Save options e Degrees display selector Help Degrees display style Parent topic The Gridding window For latitude and longitude data you can select degrees minutes seconds or decimal degrees using the Degrees display selector button on the toolbar Specifying input and output files Parent topic Gridding T22a Library Help Top INTREPID has controls for specifying the input and output datasets at logical places in the tool as well as some controls in the File menu and toolbar You can enter the path and DIR or gdb file name of the datasets in the dataset text boxes or browse using the buttons If the grid is in the workng directory see Working directory in Introduction to INTREPID R02 there is no need to enter a path Paths can be Relative to the working directory OR Abs
58. s a minimum of 20 shells around each cell When INTREPID has recorded three neighbouring original data cells for a blank cell it immediately locates all blank cells whose centroids lie within the triangle formed by the three original data points INTREPID interpolates values for all cells within the triangle and marks all of the cells in the triangle as processed INTREPID uses an honour original data process for this interpolation since it uses the actual positions of the original data points rather than their cell centroids Note The honour original data process described here uses the same information but is otherwise not related to the honour original data options provided with minimum curvature image refinement After completing a pass in which it is unable to perform any interpolation INTREPID moves to stage 2 Linear interpolation INTREPID then passes through the grid examining all of the blank cells for which it has found only two nearby original data points INTREPID interpolates values for all blank cells on the line between the two original data points once again using the position of the points rather than their cell centroids Box filtering INTREPID passes through the grid using the Box Filter method See Gridding Method Box Filter and creates values for all remaining blank cells 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding T22a 29 Library Help Top 4 Back gt
59. s in the grid e Minimum Take the smallest observation value as the cell value e Maximum Take the largest observation value as the cell value 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 28 Library Help Top 4 Back gt Gridding Method Nearest Neighbours Parent topic Gridding Method tab Library Help Top Input Subset PreProcessing Gridding Method Grid Refinement Output Gria Extrapolation Lit 5 z Cell Assignment z I Save Original Data Points l ts DIF Gridding Method Nearest_Neighbour gt I Save Triangles Weight Type Unity ha Unity Magnitude Square Root You can produce grids from line and point dataset fields using this method It has three stages 1 Triangulation INTREPID makes a number of passes through the grid It works along the rows of the grid one by one starting alternately at the most Northerly row working South and the most Southerly row working North For blank cells INTREPID locates nearby original data cells and uses a triangulation process to calculate values When it locates a neighbouring original data cell it records this for the blank cell On the first pass through the grid INTREPID searches for original data cells that are immediate neighbours On subsequent passes INTREPID searches for original data cells one cell further away each time from the blank cell This process is called shelling INTREPID searche
60. sses and parameters that you require INTREPID performs pre processing INTREPID calculates the number of cells in the grid based on the extent of the line or point data INTREPID calculates centroid values for original data cells INTREPID calculates centroid values for interpolated cells that do not contain original data using the Nearest Neighbours Bi Cubic Spline Variable data density or Box Filter methods INTREPID performs LaPlace smoothing as required INTREPID performs the Minimum Curvature smoothing process as required INTREPID performs the Masking or Clipping process as required INTREPID saves the grid if required or saves the current tile and goes back to repeat the process for the next selected tile Using the Gridding tool Parent topic In this section Gridding na F T22a Gridding tool Overview of steps interactive only Gridding scalar data Gridding vector data Gridding tensor data Gridding of potential field data with observed gradients Enhanced potential field gridding further notes 2012 Intrepid Geophysics 4 Back gt Library Help Top INTREPID User Manual Gridding T22a 3 Library Help Top 4 Back gt Gridding tool Overview of steps interactive only Parent topic gt gt To use Gridding with the INTREPID graphic user interface i h P apps z Gone iooi 1 Ifyou are launching Gridding from the Project Manager and know which dataset you want to process
61. st because it simply grids the data in the data field See Gridding scalar data If you have specified a vector or tensor field for gridding or gradient fields separate components or vector to enhance a scalar field Use this drop down list to select the product for INTREPID to grid Each type of input data has its own set of entries in this list For details see Gridding vector data Gridding tensor data Gridding of potential field data with observed gradients same options as Gridding vector data Rotation Use this spin box to specify the number of degrees of rotation for the output grid See Producing a rotated grid for details Grid Dimensions centroids Library Help Top Origin TL Bottom Right Use these spin boxes to specify the X and Y coordinates of the top left origin and bottom right points of the output grid If you set these values INTREPID automatically adjusts Extents and number of Cells Note that the coordinates defined are for the centre of the cells at the top left and bottom right of the output grid They do not define the outside bounding box of the grid ie they are half a cell inside the box limits Extents Use these spin boxes to specify the size in distance units of the grid in the X and Y directions If you set these values INTREPID automatically adjusts Bottom Right and number of Cells Cells Use these spin boxes to specify the number of cells in the grid in the X and Y
62. ta point within the cell for honour original points processes 3 INTREPID determines the row and column limits for the grid INTREPID uses the cell extrapolation limit and the original data cells at the ends of each row and column in this process Note The origin of a grid is the centroid of the cell in the top left hand corner Gridding method general parameters Parent topic These parameters apply to the gridding process no matter what method you select Gridding Method tab Input Subset PreProcessing Gridding Method Grid Refinement Output Gria Extrapolation Limit g Cell Assignment z IV Save Original Data Points JoriginalPoints DIR El Gridding Method Nearest_Neighbour v I Save Triangles Extrapolation limit Cell Assignment Save Original Data Points Save triangles Gridding method Gridding parameters summary The various Gridding processes require different selections of these parameters The following tables show Gridding parameters that are required for each method Yes means that you must specify a value Blank means that INTREPID does not use or require the parameter in the process at this stage although its effect on the data may be carried through from a previous stage ON means that the option must be turned on for the process 1 16 To be more precise the coordinates of the sub cell containing the original data point There are 128 x 128 sub cells in a grid cell Library Help Top
63. ulate values for the cells within the edge regions and also within enclosed gaps fully enclosed by but outside the edge regions INTREPID ofers a number of methods for this process You can select and specify parameters for tehm in the Gridding Method tab In this section Grid initialisation See Grid initialisation for a description of the initialisation process common to all gridding methods General parameters General parameters are common to all gridding methods See Gridding method general parameters Gridding method Nearest neighbours This is our recommended general purpose method It works well for a wide range of datasets It uses two point and three point planar interpolation triangulation See Gridding Method Nearest Neighbours Gridding method Bi cubic spline Line datasets only This method uses splining to assign cell centroid values See Gridding Method Bi Cubic Spline Gridding method Box filter This method is also successful with a wide range of datasets It does not take account of gradients in the process and will tend to reduce the magnitude and size of features in your results compared with the other methods It uses local averaging to assign cell centroid values assuming that the original data point is at the centroid of the cell If you use Nearest Neighbours or one of the Spline methods INTREPID uses the Box Filter to fill any gaps in the grid after your chosen process is complete See Griddi
64. ure Grid Relaxation Factor 1 375 vot tease E Tension 0 0 IV Honour Original Data One Cell Two Cell Vv Smoothing Iterations 2 4 In this section LaPlace iterations e Minimum Curvature Setting grid nulls 2012 Intrepid Geophysics lt 4 Back gt INTREPID User Manual Gridding lt 4 Back gt Library Help Top LaPlace iterations This is a heavy smoothing convolution filter that INTREPID applies to all initial grid estimates It leaves the original points alone The process improves the condition of the grid for the Minimum Curvature process If you perform LaPlace convolution Parent topic Grid Refinement tab Library Help Top Minimum Curvature will require fewer iterations to achieve a satisfactory The LaPlace formula appears below Where Zo is the value in the cell being processed before the adjustment Zo is the value in the cell being processed after the adjustment R is the relaxation factor Zi Z2 Z3 44 are the values in the surrounding cells as shown Zo Zo Ze If Zo does not contain original data then 1 a g Z o XR Zp Laplace iterations T22a 37 result Contact our technical support service for information about this parameter Relaxation factor See Minimum Curvature for more information about this parameter 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 38 Library Help Top 4 Back
65. vector field If you have a set of gradients stored in a field of vector type see Compound data types in INTREPID database file and data structures R05 follow these steps gt gt To specify gradients as a vector field 1 Ensure that you have specified and selected the input dataset see Specifying input and output files and Specifying several input datasets 2 Specify the scalar field that you are gridding Use the Data drop down list in the Input tab see Input tab 3 Choose Advanced INTREPID displays the Input gradients dialog box Input Data x Single Field Data Joouguer ma V Gradients G_acc_v X C Vector Field Group M Across date BA Vv Along date z Vv ertical date v 4 Select Single Field 5 Check the Gradients check box and select the gradient vector field from the Gradients drop down list 6 Choose Close 7 Inthe Output grid tab from the Product drop down list select Enhanced Signal Product Enhanced Signal Library Help Top 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 10 Library Help Top Library Help Top 4 Back gt Specifying gradients as scalar components If you have a set of gradients stored in a field of vector type see Compound data types in INTREPID database file and data structures R05 follow these steps gt gt To specify gradients as a vector field 1 Ensure that you have specified and select
66. xact coordinates of the original data If you are examining honour edit its aliases to select the set of coordinates you require See INTREPID system parameters and install cfg R07 for further information about system parameters in INTREPID and Vector dataset field aliases in INTREPID database file and data structures R05 for more information about aliases 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 27 Library Help Top Library Help Top 4 Back gt Recording the original data points used You can save a record of the data points selected for use by this gridding process the sample points selected because they were closest to the cell centroids gt gt To save the sample points used by Bi Cubic Spline gridding Assign a value to the system parameter INTREPID_FAST_POINTS before processing INTREPID will save the sample points for the process as a point dataset called fast See INTREPID system parameters and install cfg RO7 for further information about system parameters in INTREPID Extrapolation limit You need to specify cell extrapolation limits for a number of Gridding processes At the start of the gridding process INTREPID creates edge regions around the original data cells These regions will contain extrapolated interpolated data The edge regions should ideally meet or overlap to satisfactorily fill gaps between original data points e g the gap
67. xamining trends This filter is in the form of a moving average INTREPID uses the residual values from this moving average filter You can specify the size Gn grid cells of the window for the filter Minimum Anomaly INTREPID will not process maxima or minima with amplitude less than the value you specify here 1 Brindt L and Hauska H 1985 Direction dependent interpolation of aeromagnetic data Eleventh International Symposium on Machine Processing of Remotely Sensed Data Purdue University Indiana USA 2 Fitzgerald D Yassi N and Dart P 1997 A case study on geophysical gridding techniques INTREPID perspective Exploration Geophysics 28 1 2012 Intrepid Geophysics 4 Back gt INTREPID User Manual Gridding T22a 32 Library Help Top Library Help Top lt 4 Back gt Minimum Search Angle INTREPID will not record trends at angles closer to the line direction than the angle you specify here Trends close to the line direction are too hard to follow using the trend gridding method because of the oblique distances between the lines Trends in the line direction do not need enhancement in any case Save Trend Points Dataset To save the additional trend points turn on this check box and specify the name for the additional trend points dataset This option replaces the use of the INTREPID_TREND_POINTS system parameter and the procedure described in Trend Variance Factor You can save a recor

Gridding (T22a) - Intrepid Geophysics

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