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Grid Operations (T25)

The Grid Operations tool enables you to perform a wide range of operations on grid datasets. In this manual:

General
Grid operation methods
More about using Grid Operations

Introduction

Parent topic: Grid Operations (T25)

Tensor grid operations overview

The Grid Operations tool enables you to perform the following operations on both standard full tensor grids (FTG) and Falcon grids:

  • Create a tensor grid from its component grids
  • Deconstruct a tensor grid into its component grids.

General grid operations overview

The Grid Operations tool enables you to perform the following operations on grid datasets:

  • Resample a grid to change its cell size and origin. You can choose from four available smoothing methods.
  • Subsample a grid.
  • Smooth a grid using Minimum Curvature to improve its appearance.
  • Rotate a grid about the grid origin.
  • Export all non-null values from a grid to an INTREPID point dataset.
  • Extract single band grids from a multi-band grid.
  • Insert single band grids into a multi-band grid.
  • Change the precision of data in a grid.
  • Homogenise a set of grids so that they have uniform bounds and cell size.
  • Calculate the difference of two grids, without the grids needing to have the same origin and cell size.
  • Detrend a grid using the 2D least squares technology from grid filter.
  • Create GRF grids for your selected input grid. You must supply date of survey acquisition and survey flying height.
  • Capture the grid outline into a shape or polygon file.
  • Create a null grid that has the same dimensions as the input grid.

The Grid Operations tool

Parent topic: Grid Operations (T25)

Follow these steps to use the Grid Operations tool interactively. For batch mode, see Running the tool in batch mode.

To use Grid Operations interactively:
  1. In Project Manager, from the Gridding menu, choose Grid Operations or use the command gridop.exe. INTREPID displays the Grid Operations window.
  2. If you have previously prepared file specifications and parameter settings for Grid Operations, load the corresponding task specification file—see Specifying input, settings and output using a .task file for detailed instructions. If all of the specifications are correct in this file, go to step 6. If you want to modify any settings, carry out the following steps as required.
  3. gop.png
  4. Specify the input and output datasets for the operation. Specify the reference input dataset for resampling or smoothing, if required. See Specifying input and output files for detailed instructions.
  5. Select the grid operation that you require and set its parameters.
  6. gop-op-type.png
  7. If you want to record your settings so that you can re-use them, save a .task file. See Saving settings for later use for detailed instructions.
  8. Run the process. See Running the Grid Operations task interactively.
  9. If you want to repeat the process, repeat steps 2–6, varying the parameters and data files as required.
  10. To exit from this tool, see Exit from Grid Operations.

After using this tool, you can inspect the output using 3D Explore visualisation tool (See 3D Explore (T61).

For information about on-line help while you are using the tool, see Grid Operations Help.

You can also execute Grid Operations as a batch task using a task specification file that you have previously prepared. See for details.

Specifying input and output files

Parent topic: Grid Operations (T25)

To use Grid Operations, you need to specify the grid datasets to be processed and for saving the results.

In this section:

Note: The user interface for input files is different for some operations. See the sections in Specifying input manually.

Specifying input, settings and output using a .task file

You can specify input data, settings and output files for this tool by loading a .task file. From the File menu choose Open task file or press ctrl+o

jmenu-file.png

From the Load a Task File dialog box, select a .task file and then choose Open. INTREPID loads the task file and displays its settings in the tool window.

Note: Some tools have options that are available in batch mode only. If you load a .task file for interactive use and settings are not shown in the user interface then INTREPID may not apply them. It is better to run the tool in batch mode if you want to control these settings.

Specifying input manually

Specify input in the Input grids area.

Type in or paste the path and filenames or use the Browse button (ico-java-folder.png). If you use a Browse button, INTREPID displays an Open or Save As dialog box for you locate or specify the file you require. (See “Specifying input and output files” in Introduction to INTREPID (R02) for information about specifying files).

The grid operations in this tool have different input file requirements. For detailed instructions about input files for your operation, see the steps for the section that describes it.

Specifying output manually

Specify output data in the Output options area.

Type in or paste the path and filenames or use the Browse button (ico-java-folder.png). If you use a Browse button, INTREPID displays an Open or Save As dialog box for you locate or specify the file you require. (See “Specifying input and output files” in Introduction to INTREPID (R02) for information about specifying files).

gop-output.png

Viewing input file information

For any input file that is open in the tool, you can conveniently view its extents and its datum and projection.

To view file information:
  1. EITHER:
    From the Window menu choose View file info or press ctrl+i.
  2. jmenu-window-fileinfo-menu.png

    OR
    in the application window, choose Input Info java-2018-input-info-button.png.

    The Input Data Info dialog box appears.

  3. From the File info to display drop-down list, select the input dataset required.
jmenu-window-fileinfo-select.png

INTREPID displays the file information for the selected input dataset.

jmenu-file-info-example.png

Optimising processing performance for large grids

Parent topic: Grid Operations (T25)

For large grids, INTREPID uses a tiling system. This involves processing the grid a section at a time. You can optimise the performance of your computer in this task by adjusting the value of the INTREPID_MEMORY system parameter. INTREPID automatically decides whether to use the tiling process and it takes into account your INTREPID_MEMORY setting.

For information about INTREPID_MEMORY, see “INTREPID Memory limits and tiling” in Configuring and using INTREPID (R04) .

Constructing a tensor grid

Parent topic: Grid Operations (T25)

You can use Grid Operations to create tensor grids, including Falcon grids, from their component grids.

In this section:

Creating a full tensor gradient (FTG) grids from components

Use the following steps to create an FTG or other non-Falcon grid.

To create an FTG tensor grid from its components:
  1. In the Select Operation Type panel, select Operation Type > Create from Parts
  2. Ensure that you have a set of six component grids:
    • With matching size, location and cell size
    • In ERMapper (.ers) or .semi format
  3. In the Input Grids panel > Create from Parts tab specify the component grids XX, XY, ZX, YY, YZ, ZZ.
  4. gop-input-create-from-parts.png

    Use the input boxes or browse buttons for specifying the inputs

  5. In the Operation Properties panel Combination tab specify the Maximum Trace Error.
  6. gop-op-combination.png

    When we are forming a tensor grid from its component grids, we often find the component grids to not fit with some of the known physics. In particular, the sum of the Txx, Tyy, Tzz components should equal exactly zero, and this is rarely the case. This is the trace error. We specify the Maximum Trace Error as the largest acceptable error for data in the current task. If the sum is below the value specified then we still count the signal as viable.

  7. In the Output Options panel > Output Grid specify the Output Grid.
  8. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  9. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  10. general-task-completed.png

    Choose OK.

Example .task file

Here are examples of .task files for Grid Operations extraction tensor components.

Falcon dataset

Here is an example of an Grid Operations task specification file for creating a Falcon tensor grid from four component grids.

# create a Falcon tensor grid from 4 component grids! IntrepidTask { GridOp { AUV: “${cookbook}/tensors/BrokenHill_Falcon/BH_2_GRIDS/BH_AUV.ers”; ANE: “${cookbook}/tensors/BrokenHill_Falcon/BH_2_GRIDS/BH_ANE.ers”; BUV: “${cookbook}/tensors/BrokenHill_Falcon/BH_2_GRIDS/BH_BUV.ers”; BNE: “${cookbook}/tensors/BrokenHill_Falcon/BH_2_GRIDS/BH_BNE.ers”; Output: “BH_Rebuilt.ers” Method: ManipulateTensor; TensorOperation: TENSOR_Complete; OutputDataType: TensorGrid; Maximum_Tensor_Trace_Error: 20.0;# not able to be enforced for falcon anyway! } }

FTG or other tensor dataset

Here is an example of an Grid Operations task specification file for creating an FTG tensor grid from six component grids.

# create a tensor grid from 6 component grids! # unfortunately, you must run dbedit in the directory where all the grids are stored # this test when the trace condition is not exactly met, still allows the creation of a tensor grid IntrepidTask { GridOp { XX: “${examples}/datasets/TensorGradients/single_txx.ers”; XY: “${examples}/datasets/TensorGradients/single_tyx.ers”; ZX: “${examples}/datasets/TensorGradients/single_txz.ers”; YY: “${examples}/datasets/TensorGradients/single_tyy.ers”; YZ: “${examples}/datasets/TensorGradients/single_tyz.ers”; ZZ: “${examples}/datasets/TensorGradients/single_tzz.ers”; Output: “Traw.ers”; Method: ManipulateTensor; TensorOperation: TENSOR_Complete; OutputDataType: TensorGrid; } }

Creating Falcon tensor grids from components

This section is about creating Falcon grids from parts.

To create a Falcon tensor grid from its components:
  1. In the Select Operation Type panel, select Operation Type > Create From Parts
  2. Ensure that you have a set of four component grids:
    • With matching size, location and cell size
    • In ERMapper (.ers) or .semi format
  3. In the Input Grids panel > Falcon Create from Parts tab specify the component grids AUV, ANE BUV, BNE.
  4. gop-input-falcon-create-from-parts.png
  5. In the Operation Properties panel Combination tab specify the Maximum Trace Error.
  6. gop-op-combination.png

    When we are forming a tensor grid from its component grids, we often find the component grids to not fit with some of the known physics. In particular, the sum of the Txx, Tyy, Tzz components should equal exactly zero, and this is rarely the case. This is the trace error. We specify the Maximum Trace Error as the largest acceptable error for data in the current task. If the sum is below the value specified then we still count the signal as viable.

  7. In the Output Options panel > Output Grid specify the Output Grid.
  8. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  9. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  10. general-task-completed.png

    Choose OK.

Extracting components from a tensor grid

Parent topic: Grid Operations (T25)

In this section:

Available tensor grid components

Parent topic: Extracting components from a tensor grid

You can extract grids of the following components and derived values from a tensor grid.

Components overview

Components here include both Full Tensor Gradiometry (FTG) and Falcon.:

Component

Description

Auv,Ane,Buv,Bne,Guv,Gne

Falcon data components

XX, XY, ZX, YY, YZ, ZZ

Normal Component gradients

Max, Mid, Min eigenvalue

Principal components

Trace, SQRT 1st, CubeRT 2nd

1st, 2nd, 3rd scaled invariants

Ratio I2 / I1

Ratio of second to first scaled invariant. This may help to tell if causative body has 2-dimensional characteristics. See:

Pedersen L.B., Rasmussen T.M., The Gradient Tensor of Potential Field Anomalies: Some Implications on Data Collection and Data Processing of Maps. Geophysics, 55, No 12, 1558–1566.

Phase, Tensor Tilt, Tensor EigenAxis

Independent rotational component of tensor curvature. We use this for enhancing subtle features and suppressing strong features

Scalar Magnitude

David Clarke’s suggestion for a measure of invariant amplitude.

Curvature Gradient

Falcon Hilbert pair magnitude (sqrt(Guv2 + Gne2))

Attributes a value to the amount of curvature.

WormsTotalHorizontal Gradient

For scalar and tensor grids (sqrt(Tzx2 + Tyz2))

First balanced gradient

This enhancement is more like a component of the tilt angle vector. It has several advantages computationally, especially in Euler deconvolution

List of all components available for extracting from tensor grids

Some components are only available in batch mode.

Component

Notes

TENSOR_XX

TENSOR_YY

TENSOR_ZZ

TENSOR_XY

TENSOR_YZ

TENSOR_ZX

TENSOR_UV

Falcon equivalent is gradient measure

TENSOR_Determinant

Matrix property

TENSOR_Max_Eigen

TENSOR_Mid_Eigen

TENSOR_Min_Eigen

TENSOR_Trace

TENSOR_Second_Invariant

TENSOR_Ratio

TENSOR_Strike

When the causative body is 2D the mid eigen value is close to zero

TENSOR_CubeRoot_of_Determinant

TENSOR_SquareRoot_of_Second_Invariant

TENSOR_Horizontal_Gradient_Amplitude

TENSOR_Horizontal_Gradient_Direction

TENSOR_Curvature_Gradient_Amplitude

TENSOR_Curvature_Gradient_Direction

TENSOR_Octahedral_Normal

TENSOR_Octahedral_Shear

TENSOR_Complete

Output a complete tensor grid, just returning the tensor as itself, especially in gridding

TENSOR_Norm

TENSOR_Maximum_Magnitude

TENSOR_Unit_EigenVector_Volume

TENSOR_Phase

TENSOR_Modulo

TENSOR_EigenAxis

TENSOR_TILT

The near horizontal rotational component when the causative body is 2D (strike/dip)

TENSOR_BRUTE

Brute force conjugate gradient integration for Falcon

TENSOR_SCALAR_MAGNITUDE

Suggested by David Clarke

Quaternion

Rotational properties, as expressed via a quaternion representation

TENSOR_Quaternion_Real_part

TENSOR_Quaternion_I_part

TENSOR_Quaternion_J_part

TENSOR_Quaternion_K_part

TENSOR_Quaternion_RGB_Phase

Falcon

TENSOR_AUV

TENSOR_ANE

TENSOR_BUV

TENSOR_BNE

TENSOR_BRUTE_B

Balanced gradients

Exploration geophysics, 2014 Guoqing Ma. These are like a tilt angle used in Euler deconvolution. Together they are analagous to Roll, Pitch,Yaw

TENSOR_FirstBalancedGradientX

TENSOR_FirstBalancedGradientY

TENSOR_FirstBalancedGradientZ

Second balanced gradients ratio of horizontal derivatives to analytic signal

TENSOR_SecondBalancedGradientX

TENSOR_SecondBalancedGradientY

TENSOR_SecondBalancedGradientZ


Falcon Read options

From the Falcon Read drop-down list, select the version of the data you require

gop-input-falcon-read.png

Falcon_A —Use the data from the Falcon A disc.

Falcon_B —Use the data from the Falcon B disc.

Falcon_Average —Use the average of the data from the Falcon A and B discs—this is the most common practice.

Falcon_Difference —Use the difference between the data from the Falcon A and B discs—the error estimate.

Steps for extracting a component grid

To extract a grid of a component or calculated value from a tensor grid:
  1. In the Select Operation Type panel, select Operation Type > Extract Components
  2. Specify the input tensor grid. Select Input Grid.
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

    Note: Always specify the input grid before selecting the operation that you want to perform. INTREPID identifies grid type and displays corresponding options.

  5. For Falcon datasets, in the Input Grids panel select the required Falcon Read. (for details, see Falcon Read options)
  6. gop-input-falcon-read00352.png
  7. Select the component or derived value that you want to extract from the Output Grid Type drop-down menu under Operation Properties.
  8. gopmtens.png

    For information about the possible Output Grid Types see Available tensor grid components.

  9. In the Output Options panel > Output Grid specify the Output Grid.
  10. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  11. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  12. general-task-completed.png

    Choose OK.

  13. Example .task files

Here are examples of .task files for Grid Operations extraction tensor components.

Falcon dataset

This example extracts the ANE component.

# extract a tensor product/component from the tensor grid.. # Usage: fmanager -batch gridop_extract_TZZ_component.task # IntrepidTask { GridOp { Input : “${cookbook}/tensors/BrokenHill_Falcon/BH_2_GRIDS/whole_T.ers”; Output : “BH_ANE.ers”; OutputDataType: IEEE4ByteReal; Method: ManipulateTensor; TensorOperation: TENSOR_ANE; FalconQuery: FALCON_A; } } # list of tensor components, or scalar grids that can be dumped from a tensor grid # TENSOR_XX=10; # TENSOR_YY=11; # TENSOR_ZZ=12; # TENSOR_XY=13; # TENSOR_YZ=14; # TENSOR_ZX=15; # TENSOR_UV=16; // falcon equivalent gradient measure # TENSOR_Determinant=17; // matrix property # TENSOR_Max_Eigen=18; # TENSOR_Mid_Eigen=19; # TENSOR_Min_Eigen=20; # TENSOR_Trace=21; # TENSOR_Second_Invariant=22; # TENSOR_Ratio=23; # TENSOR_Strike=24; # TENSOR_CubeRoot_of_Determinant=25; # TENSOR_SquareRoot_of_Second_Invariant=26; # TENSOR_Horizontal_Gradient_Amplitude=27; # TENSOR_Horizontal_Gradient_Direction=28; # TENSOR_Curvature_Gradient_Amplitude=29; # TENSOR_Curvature_Gradient_Direction=30; # TENSOR_Octahedral_Normal=31; # TENSOR_Octahedral_Shear=32; # TENSOR_Norm=34; # // start of rotational properties, as expressed via a quaternion representation # TENSOR_Quaternion_Real_part=35; # TENSOR_Quaternion_I_part=36; # TENSOR_Quaternion_J_part=37; # TENSOR_Quaternion_K_part=38; # TENSOR_Maximum_Magnitude=39; # TENSOR_Unit_EigenVector_Volume=40; # TENSOR_Phase=41; # TENSOR_Modulo=42; # TENSOR_EigenAxis=43; # TENSOR_Quaternion_RGB_Phase=44; # TENSOR_FREQ = 45; // EM/MT tensor frequency; # TENSOR_Quaternion_Isotropic_Phase=50; # TENSOR_Quaternion_Deviatoric_Phase=51; # TENSOR_Quaternion_Modulo_Phase=52; # TENSOR_TILT = 60;

FTG or other tensor dataset

This example extracts the Tzz component.

# extract a tensor product/component from the tensor grid.. # Usage: fmanager -batch gridop_extract_TZZ_component.task # IntrepidTask { GridOp { Input : “${cookbook}/tensors/BrokenHill_Falcon/BH_2_GRIDS/whole_T.ers”; Output : “BH_ANE.ers”; OutputDataType: IEEE4ByteReal; Method: ManipulateTensor; TensorOperation: TENSOR_ANE; FalconQuery: FALCON_A; } } # list of tensor components, or scalar grids that can be dumped from a tensor grid # TENSOR_XX=10; # TENSOR_YY=11; # TENSOR_ZZ=12; # TENSOR_XY=13; # TENSOR_YZ=14; # TENSOR_ZX=15; # TENSOR_UV=16; // falcon equivalent gradient measure # TENSOR_Determinant=17; // matrix property # TENSOR_Max_Eigen=18; # TENSOR_Mid_Eigen=19; # TENSOR_Min_Eigen=20; # TENSOR_Trace=21; # TENSOR_Second_Invariant=22; # TENSOR_Ratio=23; # TENSOR_Strike=24; # TENSOR_CubeRoot_of_Determinant=25; # TENSOR_SquareRoot_of_Second_Invariant=26; # TENSOR_Horizontal_Gradient_Amplitude=27; # TENSOR_Horizontal_Gradient_Direction=28; # TENSOR_Curvature_Gradient_Amplitude=29; # TENSOR_Curvature_Gradient_Direction=30; # TENSOR_Octahedral_Normal=31; # TENSOR_Octahedral_Shear=32; # TENSOR_Norm=34; # // start of rotational properties, as expressed via a quaternion representation # TENSOR_Quaternion_Real_part=35; # TENSOR_Quaternion_I_part=36; # TENSOR_Quaternion_J_part=37; # TENSOR_Quaternion_K_part=38; # TENSOR_Maximum_Magnitude=39; # TENSOR_Unit_EigenVector_Volume=40; # TENSOR_Phase=41; # TENSOR_Modulo=42; # TENSOR_EigenAxis=43; # TENSOR_Quaternion_RGB_Phase=44; # TENSOR_FREQ = 45; // EM/MT tensor frequency; # TENSOR_Quaternion_Isotropic_Phase=50; # TENSOR_Quaternion_Deviatoric_Phase=51; # TENSOR_Quaternion_Modulo_Phase=52; # TENSOR_TILT = 60;

First balanced gradient

This enhancement is more like a component of the tilt angle vector. It has several advantages computationally, especially in Euler deconvolution.

# extract a tensor product/component from the tensor grid.. # Usage: fmanager -batch gridop_extract_FirstBalancedGradientX.task # This enhancement is more like a component of the tilt angle vector # has several advantages computationally, especially in Euler deconvolution # FirstBalancedGradientX = atan(sqrt(Txx*Txx+Txy*Txy)/Txz) etc, so a combination of the measured components, with units of radians. IntrepidTask { GridOp { Input : “${cookbook}/tensors/Aurizonia/A_2_GRIDS/auriz_line_levelled_Rotate135.ers”; Output : “aurizonia_T_fa_FirstBalancedGradientX.ers”; OutputDataType: IEEE4ByteReal; Method: ManipulateTensor; TensorOperation: TENSOR_FirstBalancedGradientX; } } # list of tensor components, or scalar grids that can be dumped from a tensor grid # TENSOR_XX=10; # TENSOR_YY=11; # TENSOR_ZZ=12; # TENSOR_XY=13; # TENSOR_YZ=14; # TENSOR_ZX=15; # TENSOR_UV=16; // falcon equivalent gradient measure # TENSOR_Determinant=17; // matrix property # TENSOR_Max_Eigen=18; # TENSOR_Mid_Eigen=19; # TENSOR_Min_Eigen=20; # TENSOR_Trace=21; # TENSOR_Second_Invariant=22; # TENSOR_Ratio=23; # TENSOR_Strike=24; // when the causitive body is 2D , mid eigne value is close to zero # TENSOR_CubeRoot_of_Determinant=25; # TENSOR_SquareRoot_of_Second_Invariant=26; # TENSOR_Horizontal_Gradient_Amplitude=27; # TENSOR_Horizontal_Gradient_Direction=28; # TENSOR_Curvature_Gradient_Amplitude=29; # TENSOR_Curvature_Gradient_Direction=30; # TENSOR_Octahedral_Normal=31; # TENSOR_Octahedral_Shear=32; # TENSOR_Complete = 33; // output a complete tensor grid;// just return the tensor as itself, especially in gridding # TENSOR_Norm=34; # start of rotational properties, as expressed via a quaternion representation # TENSOR_Quaternion_Real_part=35; # TENSOR_Quaternion_I_part=36; # TENSOR_Quaternion_J_part=37; # TENSOR_Quaternion_K_part=38; # TENSOR_Maximum_Magnitude=39; # TENSOR_Unit_EigenVector_Volume=40; # TENSOR_Phase=41; # TENSOR_Modulo=42; # TENSOR_EigenAxis=43; # TENSOR_Quaternion_RGB_Phase=44; # TENSOR_TILT = 60; // the near horizontal rotational component when the causitive body is 2D ( strike/dip) # TENSOR_BRUTE = 61; // brute force conjugate gradient integration for Falcon # TENSOR_SCALAR_MAGNITUDE = 62; /// david clarke special # TENSOR_AUV = 63; // falcon # TENSOR_ANE = 64; # TENSOR_BUV = 65; # TENSOR_BNE = 66; # TENSOR_BRUTE_B = 67; # balanced gradients, exploration geophysics, 2014 Guoqing Ma # like a tilt angle, used in Euler deconvolution, so together, analagous to Roll, Pitch,Yaw # TENSOR_FirstBalancedGradientX = 70; # TENSOR_FirstBalancedGradientY = 71; # TENSOR_FirstBalancedGradientZ = 72; # second balanced gradients ratio of horizontal derivatives to analytic signal # TENSOR_SecondBalancedGradientX = 73; # TENSOR_SecondBalancedGradientY = 74; # TENSOR_SecondBalancedGradientZ = 75;

Resampling a grid

Parent topic: Grid Operations (T25)

In this section:

Introduction to resampling

Resampling creates a new grid with a specified cell size and an origin based on a specified reference grid. If you do not specify a reference grid, INTREPID uses the origin of the input grid. It uses an interpolation process to calculate the value for each output cell. The output cell size may be larger or smaller than the input grid cell size. The output cell size does not need to be an exact multiple of the input grid cell size.

Each cell value in the output grid is derived from a single input grid cell or a group of neighbouring input grid cells. There are four resampling methods available to interpolate values for the output cells. They are Newton 4th Order, Cubic Spline, Minimum Curvature or Cubic Polynomial.

Input and output for Resampling

Specify the original grid as the Input Grid. You can set the origin of the new grid to that of an existing grid. Set the existing grid as the Reference Grid.

For an example of a situation where you would want to change the origin, see Resampling for grid merges).

Specify a name for the output grid (the resampled grid).

Resampling methods—introduction

Grid Operations provides four resampling methods:

Resampling – Newton 4th Difference— This is our recommended general purpose method. It works well for a wide range of datasets. It is the best method to use for radiometric or electromagnetic data. It computes quickly on large grids, and honours the original values faithfully. See Resampling—about Newton 4th Difference

Resampling – Cubic Spline— This is best suited to datasets with small amplitude changes between cells (ie; not radiometric or electromagnetic data). It is slower to compute than Newton 4th order. See Resampling—about Cubic Spline

Resampling – Cubic Polynomial— This is especially suited to potential field data. This method ensures the highest quality local estimates of a field that is Laplacian. It provides genuinely 2-dimensional interpolation, rather than one-dimensional interpolation applied in orthogonal directions. See Resampling—about Cubic Polynomial

Resampling – Minimum Curvature— This is especially suited to potential field data. It is our recommended method for magnetic or gravity datasets. It also computes quickly on large grids, and honours original values well. See Resampling—about Minimum Curvature

Resampling—about Newton 4th Difference

This method calculates the value for the new cell from the values of the 5 nearest non-Null cell values. INTREPID adjusts the new value using the 4th difference to allow for the gradient in that neighbourhood. The following diagram illustrates the process.

Resampling—about Cubic Spline

This method involves two passes.

In the first pass, INTREPID uses spline curves along the rows to calculate values that will correspond to the columns in the resampled grid.

In the second pass, INTREPID uses the column values obtained in the first pass (and original data values wherever the column coincides with a column from the original dataset) to calculate a spline curve along each resampled column. The following diagram illustrates the process.

INTREPID uses a spline curve to calculate the value for each new cell centroid in each column as illustrated in the following diagram.

Resampling—about Cubic Polynomial

The Cubic Polynomial method is applicable to resampling within a grid cell, where the values of the field at the corners and also the gradients, are known quantities. An analytic function is used locally to calculate the field value at the required point. This method is often used in contouring as well, to ensure high quality local estimates of a field that is Laplacian.

Resampling—about Minimum Curvature

INTREPID calculates the value of the new cell centroid using a weighted combination of surrounding original cell values in one pass. The Minimum Curvature resampling process uses values from the current original grid row, and from the two grid rows either side of the current grid row. This method is an inverse of the Honour Original Data method (See “Minimum Curvature” in Gridding (T22a)). The following diagrams illustrate the process.

Resampling steps

Grid Operations resamples the grid and then applies the smoothing method of your choice to the output grid. The smoothing stage is optional and you can turn it off by setting the number of smoothing iterations to zero.

To resample a grid
  1. In the Select Operation Type panel, from the Operation Type drop-down list, select the resampling option with the smoothing method that you require. .
  2. gop-op-resample-menu.png
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

    For descriptions of the methods, see:

  5. Specify the grid cell size required for the resampling process. Select Output Grid Cellsize from the Operation Properties.
  6. gop-op-resample-prop.png

    You must specify the cell size before resampling the dataset. (The Cell Size text box may not contain the cell size of the input dataset.) Specify the required cell size for the output dataset (in the distance units of the dataset) and choose OK.

    Note: If your dataset is geodetic (latitude and longitude) you need to specify the Grid Cell Size in degrees.

  7. In the Output Options panel > Output Grid specify the Output Grid.
  8. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  9. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
general-task-completed.png

Choose OK.

Example .task files

Here are examples of .task files for Grid Operations resampling.

Tensor dataset

This example uses the Cubic Polynomial method.

# # Example job file - gridop # # Resamples a tensor grid to a different cell size # actually, the resample also invokes the SLERP methods, via only the chosen Cubic_OP , no other option will work for tensors. # # Usage: fmanager -batch gridop_resample_tensor.task # IntrepidTask { GridOp { Input: “${cookbook}/SyntheticModels/S5_GRIDS/coal_seam_redone.ers”; Output: “coal_seam_redone_resample.ers”; Method: Cubic_OP;# resample with a cubic equations, not a spline OutputDataType: TensorGrid; Cellsize: 10.0; }}

Scalar dataset

This example uses the Cubic Polynomial method.

# # Example job file - gridop # # Resamples a grid to a different cell size # # Usage: fmanager -batch gridop_resample.task # IntrepidTask { GridOp { Input: “${examples}/datasets/mlevel_grid.ers”; Output: “mlevel_grid_resample.ers”; Method: Cubic_OP; OutputDataType: IEEE4ByteReal; Cellsize: 40.0; }}

Resampling and resizing a grid

Parent topic: Grid Operations (T25)

In this section:

Resampling and resizing with Grid Operations

INTREPID resamples the input grid with specified cell dimensions using the cubic polynomial method. No smoothing is applied to the grid. New bounds for the grid can be defined used X min, X max, Y min, Y max.

To resample and resize a grid using Grid Operations
  1. In the Select Operation Type panel, select Operation Type > Resample and Resize
  2. Specify the Input Grid
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  5. Specify values for X min, X max, Y min, Y max and cell dimensions X Cell, Y Cell.
  6. gop-resample-resize.png
  7. In the Output Options panel > Output Grid specify the Output Grid.
  8. gop-output.png

    For detailed instructions about output, see Specifying output manually.

    Tip: If you don’t specify a file type INTREPID will create a .ers file by default.

  9. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  10. general-task-completed.png

    Choose OK.

Resampling for grid merges

Parent topic: Resampling and resizing a grid

When you are merging grids it is normal practice to prepare them by matching their cell sizes. You can do this with Grid Operations or Grid Merge.

Resampling for grid merges using Grid Operations

In some situations you may want to combine a pair of grids with minimal Grid Merge tool resampling. Using Grid Operations you can specify an origin and cell size for the resampled grid so that it fits neatly with the grid with which you intend to merge it. For minimum Grid Merge resampling, the cell size of one grid needs to be a whole number multiple of the cell size of the other grid.

Using Grid Merge to pre-minimise resampling

The INTREPID Grid Merge tool has a resampling scheme superior to the earlier GridStitch. This reduces the need to perform resampling in Grid Operations.

To prepare grids for low resample merging

If you want to stitch grids A and B, and you will be resampling grid A to fit with grid B (the reference grid), follow these steps in the Grid Merge tool:

  1. Specify grid A as the input grid and grid B as the reference grid.
  2. Specify a new grid cell size for the resampled dataset (A').

    For no resampling of A' by Grid Merge specify the cell size of A' equal to that of B.

    INTREPID produces a resampled dataset (A') whose origin is a whole number of reference grid cells away from the origin of the reference grid (B).

  3. Smooth grid A' if necessary.

You can then use Grid Merge to stitch grids A' and B with minimal or no resampling.

Specify grid B as the grid to Calculate Geographic Reference From.

Specify the output cell size (Mesh Size) the same as that of grid B.

Grid Merge will still perform adjustment and feathering as specified by you.

For full instructions on the use of the Grid Merge tool see GridMerge—merging multiple grids (T24).

Subsampling a grid

Parent topic: Grid Operations (T25)

INTREPID decreases the resolution of the grid by keeping cells at specified increments along row and column (sample and line). The value of the kept cell becomes the value for the new larger cell.

For tensor grids, INTREPID automatically applies SLERP (Spherical Linear intERPolation) methods to make the best estimate of the signal. See https://en.wikipedia.org/wiki/Slerp

See also Dataset Refactor (T25a) for other methods of resampling data.

To subsample a grid
  1. In the Select Operation Type panel, select Operation Type > Subsampling
  2. Specify the Input Grid
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  5. Define the Sample Increment, Line Increment, First Sample, First Line, Number of Samples and Number of Lines as necessary.
  6. gop-subsample.png

    With a Sample Increment and Line Increment of 2, INTREPID samples every second cell in every second line and produce cells in the output grid that are 4 times as large. The output grid will have one quarter of the data that was in the input grid. In the same way, with a value of 3, INTREPID samples every third cell or line or both.

    Use First Sample and First Line to specify the first cell and the first line to sampled.

    You can use Number of Samples and Number of Lines to define a subsection of the dataset.

  7. In the Output Options panel > Output Grid specify the Output Grid.
  8. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  9. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  10. general-task-completed.png

    Choose OK.

Smoothing a grid

Parent topic: Grid Operations (T25)

You may have a grid that, for some reason, appears pixelated. You can improve its appearance by smoothing it. Specify your grid as the input grid.

INTREPID uses a minimum curvature smoothing process. It performs several smoothing iterations, examining and adjusting each cell in the input grid according to the values of the cells in the corresponding region. It repeats the process until:

  • It has done the number of iterations that you specified OR
  • The maximum residual change for all interpolated cells is less than the value you specify.
To smooth a grid
  1. In the Select Operation Type panel, select Operation Type > Smoothing
  2. In the Input Grids panel > Input Grids tab specify the Input Grid.
  3. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  4. Choose Smoothing from the Operation Type menu.
  5. gopmsmoo.png
  6. In the Operation Properties > Smoothing tab specify the stage at which you consider that the cell values are sufficiently settled.
  7. gopmpara.png
    • Use Number of Iterations to specify the number of times that INTREPID may scan through the grid during the Minimum Curvature smoothing process.
    • Specify the Maximum Residual.

    Each time INTREPID scans in its attempt to smooth the grid, it may cause a change in the value of each cell. As it completes each scan, the change in each cell becomes smaller—the interpolated values are becoming settled.

    When all cell changes in a pass are less than the Maximum Residual, the process terminates. Specify the Maximum Residual in the same units as the cell data.

  8. In the Output Options panel > Output Grid specify the Output Grid.
  9. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  10. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  11. general-task-completed.png

    Choose OK.

Rotating a grid

Parent topic: Grid Operations (T25)

The Grid Operations tool can rotate a grid dataset. The result is a change in the orientation of the grid rows and columns.

INTREPID performs grid rotation around the grid origin. Positive angles are anti-clockwise. You may specify the rotation angle parameter in two possible ways:

  • The output grid rotation angle OR
  • A rotation through the specified angle.

Reasons for rotating a grid

Parent topic: Rotating a grid

When you are using INTREPID there are two situations where you may want to rotate a grid.

  • The INTREPID Bicubic Spline algorithm creates a rotated grid if the survey lines were not acquired in a North–South or East–West direction. In this case you would use the Grid Operations tool to unrotate the grid back to a rotation angle of zero.
  • If you want to use the INTREPID Decorrugation tool, this tool requires that the input grid have rows and columns with North–South or East–West orientation. However the INTREPID Minimum Curvature gridding algorithm creates grid columns which run parallel to the survey lines. For survey lines which were not acquired in a North–South or East–West direction, the grid rows and columns will not have North–South or East–West orientation. In this case you will need to use Grid Operations to rotate the grid such that the input grid is correctly oriented for for Decorrugation.

Steps for rotating a grid

Parent topic: Rotating a grid

Follow these instructions:

To rotate a grid dataset
  1. In the Select Operation Type panel, select Operation Type > Rotation.
  2. prjbrota2.png
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  5. Specify the angle to or by which you wish to rotate the grid. Do this by either:
    • Selecting the target angle (Output Rotation Angle) OR
    • The amount of rotation (Rotate Through Angle).

    Specify the angle in degrees (positive angles are anticlockwise) in the text box corresponding to the selected option.

    prjbrota.png
  6. Select the Rotate Method from the drop-down list:
  7. gop-rotate-method.png
  8. When you are rotating grids, you can also change their precision. Use the Precision tab to select the precision that you require. For detailed instructions, see Changing grid precision.
  9. In the Output Options panel > Output Grid specify the Output Grid.
  10. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  11. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  12. general-task-completed.png

    Choose OK.

Example .task file

Here is an example of a .task file for Grid Operations rotating a grid.

# # Example job file - gridop # # Rotate a grid # # Usage: fmanager -batch gridop_rotate.task # IntrepidTask { GridOp { Input: “${examples}/datasets/mlevel_grid.ers”; Output: “mlevel_grid_rotated.ers”; Method: Rotate; RotateMethod: Cubic; OutputDataType: IEEE4ByteReal; Cellsize: 80.0; OutputRotation: 45.0; }}

Dumping non-null grid values to point datasets—rows or columns

Parent topic: Grid Operations (T25)

This operation uses the non-null values in your input grid to create a standard INTREPID point dataset containing X, Y, Signal fields. This is a "reverse" gridding process that enables you to regain some of the original observations from a grid. This can be useful for work with 3D GeoModeller, as you sometimes need just a few points to indicate the observation of a contact. See also the Dataset Sampler tool for similar functionality: Dataset Refactor (T25a).

Tip: When you specify output of a point dataset, you must include a database extension, for example, ..DIR. This tells Grid Operations that you require a vector dataset output, not a grid dataset.

To export dataset rows or columns to a point dataset
  1. In the Select Operation Type panel, select Operation Type > Dump Dataset Rows or Dump Dataset Columns as required.
  2. gop-type-dump.png
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  5. In the Operation PropertiesDump tab select the Coordinate System you require for the point dataset that you are creating.
  6. gop-dump.png

    Elevation or tensor coordinate conventions—Select the coordinate convention required from ENU, END, NED, WSD, WSU, Local. DTM grids usually have an elevation, so positive Z is up. For more information, see “Axes conventions” in INTREPID database, file and data structures (R05).

    rand-mag-dip-elev-conv.png
  7. If you want to subsample the output dataset to control its size, check Enable Subsampling of Output. INTREPID enables the Subsample tab
  8. gop-dump-subsample.png

    In the Subsample tab specify the sampling rate for columns and rows of the grid.

    gop-dump-subsample-tab.png

    With a Sample Increment and Line Increment of 2, for example, INTREPID converts every second cell in every second line. The number of data points in the output point dataset 25% of the number of cells in the input grid dataset.

    In the same way, with a value of 3 in both the Sample Increment and Line Increment INTREPID samples every third cell in every third line and the resulting point dataset will have about 1/9 or 11% of the number of cells in the input grid dataset.

    In this context you cannot specify the first sample or line and nor can you limit the number of samples or lines.

  9. In the Output Options panel > Output Grid specify the Output Grid.
  10. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  11. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  12. general-task-completed.png

    Choose OK.

Example .task files

Here are examples of .task files for Grid Operations dumping values to point datasets.

Tensor dataset

# # Example V6.0 file - gridop # # dump a grid into a line dataset # # Usage: fmanager -batch gridop_dump_dataset.task # IntrepidTask { GridOp { Input: “${cookbook}/tensors/Aurizonia/A_2_GRIDS/aurizonia_BG_200_tensor_nomitre.ers”; Output : “auriz_tensor..DIR” #Method : Dump_Dataset_Columns Method : Dump_Dataset# dump any non-null data into a database from the grid by rows OutputDataType : IEEE4ByteReal Subsample { SINC: 3;# every 3rd sample LINC: 2;# every second line } }}

Scalar dataset

# # Example V6.0 file - gridop # # dump a grid into a line dataset # # Usage: fmanager -batch gridop_dump_dataset.task # IntrepidTask { GridOp { Input: “${examples}/datasets/mlevel_grid.ers”; Output : “mlevel..DIR” #Method : Dump_Dataset_Columns Method : Dump_Dataset# dump any non-null data into a database from the grid by rows OutputDataType : IEEE4ByteReal Subsample { SINC: 3;# every 3rd sample LINC: 2;# every second line } }}

Extracting a band from a multiband grid

Parent topic: Grid Operations (T25)

This option enables you extract a new single band grid from an existing multiband grid.

To extract a single band grid from a multiband grid:
  1. In the Select Operation Type panel, select Operation Type > Get Band.
  2. Specify the Input Grid
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

    gop-input-multiband.png
  5. In Operation PropertiesBand tab select the band you require from the Get Band drop down list. The list may contain band names or just band numbers.
  6. gop-op-multiband.png
  7. In the Output Options panel > Output Grid specify the Output Grid.
  8. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  9. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  10. general-task-completed.png

    Choose OK.

Example .task file

Here is an example of a .task file for Grid Operations extracting a band from a multiband grid.

# # Example job file - gridop # # Get Band (extract one band from a multiband grid) # # Usage: fmanager -batch gridop_get_band_2.task # IntrepidTask { GridOp { Input: “${examples}/datasets/Newcastle_Radiometrics.ers” Output: “Newcastle_Radiometrics_Band_2.ers” Method: GetBand GetBand: 2 } }

Appending a new band to a multiband grid

Parent topic: Grid Operations (T25)

This option enables you to combine existing single band grids into a new multiband grid.

To append grids to create a multiband grid:
  1. In the Select Operation Type panel, select Operation Type > Append Bands
  2. In the Input Grids panel > Input Grids tab specify the Input Grid and Reference Grid.
  3. gop-input-single-ref.png

    For detailed instructions about input, see Specifying input manually

    The Reference Grid can be either single-band or multi-band. Ensure that it has geolocation in common with the Input grid.

    In Object Properties INTREPID enables the Band tab, but no parameters are required.

  4. In the Output Options panel > Output Grid specify the Output Grid.
  5. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  6. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  7. general-task-completed.png

    Choose OK.

  8. Repeat steps 1–4 until you have populated each band of your multiband grid.

Example .task file

Here is an example of a .task file for Grid Operations appending bands to a multiband grid.

# # Example job file - gridop # # Put Band (append bands to another grid) # # Usage: fmanager -batch gridop_put_band.task # IntrepidTask { GridOp { Input: “${examples}/datasets/Newcastle_Radiometrics.ers” Reference: “${examples}/datasets/Newcastle_Radiometrics.ers” Output: “Newcastle_Radiometrics_Combined.ers” Method: PutBand } }

Changing grid precision

Parent topic: Grid Operations (T25)

Using this option you can change the precision of the grid data. INTREPID has a range of data precisions available.

Follow these steps

To change precision of a grid:
  1. In the Select Operation Type panel, select Operation Type > Change Precision.
  2. In the Input Grids panel > Input Grids tab specify the Input Grid.
  3. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  4. In the Operations Properties panel > Precision select your required precision. For more information see Output precision.
  5. gop-op-precision.png
  6. In the Output Options panel > Output Grid specify the Output Grid.
  7. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  8. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  9. general-task-completed.png

    Choose OK.

Output precision

See “Data types in INTREPID datasets” in INTREPID database, file and data structures (R05).

fft-output-precision.png

Example .task file

Here is an example of a .task file for Grid Operations changing grid precision.

# # Example job file - gridop # # Change precision (aka. promote) # # Usage: fmanager -batch gridop_change_precision.task # IntrepidTask { GridOp { Input: “${examples}/datasets/mag_tmi.ers”; Output: “mag_tmi_promoted.ers”; Method: ChangePrecision; OutputDataType: IEEE8ByteReal; }}

Homogenising grids

Use Homogenise grids to adjust a set of grids so that their cell-sizes and bounds all match. This enables you to carry out grid arithmetic.

To homogenise grids
  1. In the Select Operation Type panel, select Operation Type > Homogenize Grids.
  2. gop-input-homogenise.png
  3. Specify the Input Grids using:
    • Add – Enter or paste the full path of the grid in the Add files text box and then choose Add – OR
    • Browse and Add– Choose Browse and Add and then browse to the required dataset
    gop-browse-homogenise-grid.png

    INTREPID lists the grids you have selected in the Homogenize Grids panel.

    To remove a grid that you don’t require, choose Remove for that grid.

    gop-homogenise-grid-collection.png

    There are no Operation Properties for this operation.

  4. In the Output Options panel > Output Grid specify the Output Grid.
  5. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  6. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  7. general-task-completed.png

    Choose OK.

Example .task file

Here is an example of a .task file for Grid Operations homogenising grids.

# # Example job file - gridop # # take a collection of grids from same area, find smallest cellsize, resample and output all grids to finest cellsize # the output griud has “_out” appended to its name # Usage: fmanager -batch gridop_makesame.task # IntrepidTask { FileManager { Action: Copy Input: “${tutorial}/Gridmerge/Raw/Beatrice_Mag.ers” Output: “./Beatrice_Mag.ers” } } IntrepidTask { FileManager { Action: Copy Input: “${tutorial}/Gridmerge/Raw/MilingimbiSub_Mag.ers” Output: “./MilingimbiSub_Mag.ers” } } IntrepidTask { FileManager { Action: Copy Input: “${tutorial}/Gridmerge/Raw/WestArnhemSub_Mag.ers” Output: “./WestArnhemSub_Mag.ers” } } IntrepidTask { GridOp { Input : “./Beatrice_Mag.ers”; Input : “./MilingimbiSub_Mag.ers”; Input : “./WestArnhemSub_Mag.ers”; Method: MakeSame; } }

Calculating the difference of two grids

Parent topic: Grid Operations (T25)

Takes an input grid and reference grid, then subtracts the input grid from the reference grid.

To create a grid that is the difference between two input grids
  1. In the Select Operation Type panel, select Operation Type > Difference
  2. In the Input Grids panel > Input Grids tab specify the Input Grid and Reference Grid.
  3. gop-input-single-ref.png

    For detailed instructions about input, see Specifying input manually

    The bounds and cell-size of the grids need to be similar, but don’t have to be identical.

    There are no Operation Properties for this operation.

  4. In the Output Options panel > Output Grid specify the Output Grid.
  5. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  6. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  7. general-task-completed.png

    Choose OK.

Example .task file

Here is an example of a .task file for Grid Operations difference of two grids.

# # Example job file - gridop # # do a spatial grid difference.. does not require 100% overlap, or same cell size # compare what an RTP operation, using equivalent layer technique, has done to the measured magnetic signal # Usage: fmanager -batch gridop_difference.task # IntrepidTask { GridOp { Input : “${examples}/datasets/equivalent_layer/tmi55.ers”; Reference : “${examples}/datasets/equivalent_layer/tmi90.ers”; Output : “difference.ers”; Method: Difference; } }

Detrending a grid

Parent topic: Grid Operations (T25)

This operation creates an output grid that is detrended using the same 2D polynomial technology used in the Spectral domain grid filters tool (GridFFT). For more information about that method, see Spectral domain grid filters tool (GridFFT) (T40).

To detrend a grid
  1. In the Select Operation Type panel, select Operation Type > Detrend.
  2. In the Input Grids panel > Input Grids tab specify the Input Grid.
  3. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  4. In the Operations Properties panel > Detrend enter your required Detrend Polynomial Degree.
  5. gop-detrend.png
  6. In the Output Options panel > Output Grid specify the Output Grid.
  7. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  8. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  9. general-task-completed.png

    Choose OK.

Creating geomagnetic reference field (GRF) grids

Parent topic: Grid Operations (T25)

The Geomagnetic option creates three grid datasets with the extents of the input grid. It creates grids of the the amplitude, inclination and declination of the Earth’s magnetic field. INTREPID calculates them using the IGRF theoretical model.

You need to specify a survey flying height above the spheroid (GPS height) and the survey acquisition date.

INTREPID creates three grid datasets. They have the same name as the output dataset you specify, but with _amplitude, _inclination and _declination appended.

This feature can be useful for comparing trends in your supplied dataset with predicted theory.

You may also want to restore a regional trend to your dataset. You can use the Spreadsheet editor tool to add this trend back into your input grid.

To create a GRF grid
  1. In the Select Operation Type panel, select Operation Type > Geomagnetic.
  2. In the Input Grids panel > Input Grids tab specify the Input Grid.
  3. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  4. Calculate the IGRF data for the input grid.
  5. In Operation Properties > GRF tab choose IGRF.

    INTREPID displays the IGRF Properties dialog box. See International geomagnetic reference field (IGRF) dialog box in this section for details.

    Adjust any values as required and choose Apply to Task.

    gop-grf-result.png
  6. In the Output Options panel > Output Grid specify the Output Grid.
  7. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  8. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
general-task-completed.png

Choose OK.

International geomagnetic reference field (IGRF) dialog box

Use this dialog box to look up the IGRF for the location you are studying.

igrf-selector.png

Time and location

Use these controls to enter the time and location of the survey.

Day, Month Year time of the survey

Epoch x

Altitude—Altitude of the survey instrument

Latitude, Longitude—Latitude and Longitude of survey

Resultant field

INTREPID displays the IGRF for the time and location that you specified.

Magnetic field strength Earth magnetic field strength at the location of the survey instrument

Declination Earth magnetic field declination at the location of the survey instrument

Inclination Earth magnetic field declination at the location of the survey instrument

Push to task file

Use this control to send the IGRF information to the INTREPID application that your are using, store it in the .task file for the current operation and return the INTREPID application you are using.

Example .task file

Here is an example of a .task file for Grid Operations creating GRF grids.

# for a magnetic grid, compute the IGRF model terms and save to 3 grids # in this case, after the task has completed, you can see the 3 auxiliary grids # amplitude: ${examples}/datasets/mlevel_grf_amplitude.ers # declination: ${examples}/datasets/mlevel_grf_declination.ers # inclination: ${examples}/datasets/mlevel_grf_inclination.ers IntrepidTask { FileManager { Action: Copy Input: “${examples}/datasets/mlevel_grid.ers” Output: “./mlevel_grid.ers” } } IntrepidTask { GridOp { Input: “./mlevel_grid.ers”; Output: “mlevel_grf.ers” Method: GeoMagnetic IGRF { Magnitude: 31992.57 Inclination: -30.23 Declination: -4.93 SurveyYear: 2018 SurveyMonth: 9 SurveyDay: 5 Elevation: 0.0 } } }

Creating a grid outline polygon

The Outline option creates a polygon dataset that describes the boundaries of the input grid.

Steps to follow

To create a grid outline polygon:
  1. In the Select Operation Type panel, select Operation Type > Outline.
  2. Specify the Input Grid
  3. In the Input Grids panel > Input Grids tab specify the Input Grid.
  4. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

  5. In the Output Options panel > Output Grid specify the Output Grid.
  6. gop-output.png

    For detailed instructions about output, see Specifying output manually.

    If you wish to output a .shp file you will need to add the extension manually. If there is no extension INTREPID will output a ..DIR.

  7. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  8. general-task-completed.png

    Choose OK.

Example .task file

Here is an example of a .task file for Grid Operations creating an outline polygon.

# # This job file create a sub-directory called ‘outlines’, and for each # grid defined in the list, runs gridop and generates an # outline polygon. IntrepidTask { GridOp { Input: “${tutorial}/Gridmerge/Raw/Beatrice_Mag.ers”; Outline: “outline_Beatrice_Mag.shp”; Method: Outline;# create a polygon of the bounding edge of a grid }}

Creating a null grid

Parent topic: Grid Operations (T25)

The Create Null Grid option produces an output grid whose cells all have the value null. The output grid has the same bounds, datum and projection as the input grid.

To create a null grid based on the input grid
  1. In the Select Operation Type panel, select Operation Type > Create Null Grid.
  2. In the Input Grids panel > Input Grids tab specify the Input Grid.
  3. gop-input-single.png

    For detailed instructions about input, see Specifying input manually

    There are no Operation Properties for this operation.

  4. In the Output Options panel > Output Grid specify the Output Grid.
  5. gop-output.png

    For detailed instructions about output, see Specifying output manually.

  6. Choose Run. INTREPID creates a .task file for your specifications and then executes it. It displays a message box showing the file name and location of the .task file.
  7. general-task-completed.png

    Choose OK.

Running the Grid Operations task interactively

Parent topic: Grid Operations (T25)

When you are satisfied with your settings, run the operation that you have prepared and view the results.

To run the task:

  • From the File menu choose Run OR
  • From the bottom right corner of the window, choose Run. OR
  • Press ctrl+r
jmenu-file-run.png

See also:

Running the tool in batch mode

Saving the resulting grid

Grid Operations saves data:

Displaying options and using task specification files

Parent topic: Grid Operations (T25)

This section has information about .task file operations with this tool:

Displaying current tool settings

Parent topic: Displaying options and using task specification files

You can, of course, examine the settings in the Grid Operations window.

Alternatively, for a complete, convenient list of all settings, save a .task file. You can then examine the current tool settings in the .task file using a text editor. See Saving settings for later use.

Saving settings for later use

You can save the current settings to a .task file. This enables you to repeat the operation later with the same settings. You can also change the settings by editing the file. For more information about .task files, see INTREPID task, HISTORY, report and log files (R06). To save the .task file, use options in the File menu:

jmenu-savetask.png

Save Task File— If you want to save the current file specifications and parameter settings in the current task specification (.task) file, use this option. If there is no current file then INTREPID prompts you to specify a name for the new file. Shortcut keystroke: ctrl+s

Save Task File As— If you want to save the current file specifications and parameter settings as a new task specification (.task) file or to replace an existing one, use this option. INTREPID prompts you to specify a name for the new file. Shortcut keystroke: ctrl+shift+s

Running the tool in batch mode

Parent topic: Displaying options and using task specification files

You can run this tool in batch mode.

To use a task specification file for a batch mode Grid Operations task

Type the command gridop.exe with the switch -batch followed by the name of the task specification file.

For example, if you had a task specification file called surv329.task in the current directory, you would use the command:

gridop.exe –batch surv329.task

Task specification file examples

You can find .task file examples within the sections on the various Grid Operations methods.

Grid Operations Help

Parent topic: Grid Operations (T25)

You can find Help for this tool:

  • In this manual
  • In tool tips that the tool displays for most screen elements. Point to an element and the relevant tool tip appears.

To open this manual from the tool, choose Help > Open Manual.

jmenu-help00409.png

Exit from Grid Operations

Parent topic: Grid Operations (T25)

To exit from this tool, choose File > Exit from the menu or press ctrl+q.

jmenu-exit.png

If you have unsaved settings in the tool, INTREPID displays a warning about saving your current settings.

java-2018-unsaved.png

Save— Save the current settings into the current .task file and then exit.

Don’t Save— Exit without saving any current settings.

Cancel— Close the warning box and return to the tool window with its current settings unchanged. Use this option if you want to save the current settings to a new .task file.