Grid File Utilities

Function

This command has many functions to modify grid files. The modifications can be done manually and in a batch mode using the grid macros. To modify manually, start by picking the Select Grid(s) button. There is another option to use inclusion and exclusion polylines. With this option active, the program will prompt for inclusion and exclusion polylines when a grid action is started. Only grid cells inside the inclusion polylines will be modified. Grid cells inside the exclusion polylines will not be modified. If no inclusion and exclusion polylines are selected, then the entire grid will be modified. Each function is described below.

• Max Value: Compares a grid and a value and takes the Maximum value of either. This is a way to stop a grid from going negative, below zero.
  
• Max Grids Compares a grid with another grid and takes the Maximum (higher) value of either.
• Min Value: Compares a grid and a value and takes the Minimum value of either. This is a good way to cap a grid off at a certain value so it never goes higher than the specified value.
  
• Min Grids: Compares a grid with another grid and takes the Minimum (lessor) value of either.
• Less Value: Asks for a value to compare and a value to assign and uses the following logic:
  If GridA < compare_value then GridA =assign_value, otherwise no change
• Less Grids: Asks for a grid to compare and a grid to assign and uses the following logic:
  If GridA < compare_GridB then GridA = GridC, otherwise no change
• Greater Value: Asks for a value to compare and a value to assign and uses the following logic:
  If GridA > compare_value then GridA =assign_value, otherwise no change
• Greater Grids: Asks for a grid to compare and a grid to assign and uses the following logic:
  If GridA > compare_GridB then GridA = GridC, otherwise no change
• Add Value: Adds an entered value to the grid values. (GridA + X)
  
• Add Grid: Adds one grid to another grid. (GridA + GridB)
  
• Subtract Value: Subtracts an entered value from the grid values. (GridA - X)
• Subtract Grid: Subtracts one grid from another grid. (GridA - GridB)
• Multiply Value: Multiplies the grid values by an entered value. (GridA * X)
• Multiply Grid: Multiplies the grid values by another grid. (GridA * GridB)
• Divide Value: Divides the grid values by an entered value. (GridA / X)
• Divide Grid: Divides the grid values by another grid. (GridA / GridB)
• Power Value: Raises the grid values to the specified power. (GridA squared, or Grid A to the 1.8 power)
• Power Grid: Raises the grid values to another grid for the "power". (GridA raised to GridB)
• Set Value: assigns the grid elevations to the user-specified value. For example by using Set Value with the inclusion perimeter option, you could set the grid values to 0.0 within the inclusion polyline for a strata thickness grid. The four options are Value to Value which will set all values to one value, Null to Value, which will set all Nulls to one value, Null to Grid, which will set all Nulls to another specified grid and Value to Null, which will set all values to Null. Using inclusion and exclusion perimeters are usually required for this command.
  

• Extrapolate: can be used to assign elevations to all grid corners by any of four methods. Global Trend finds the average slope and slope direction from the existing grid elevations and applies this slope to calculating the missing elevations. Average method calculates a grid elevation as the average of its nearest neighbors. Projected method extends the trend at the edge. Combined method uses both Average and Projected.
  
• Change Position: This lets you change the lower left and upper right corners of the grid file. For example, you can use this routine to localize a grid file if you have a large grid for the entire site but are currently working on a smaller area. If the new position covers area outside the original position, any grid cells in this area will be assigned a null value. Otherwise the program uses the original grid values for the new grid position.
• Change Resolution: This changes the grid resolution (number or dimensions of grid cells). The program uses the original grid values for calculating the grid values at the new resolution. Enter a new value for X and Y number of cells or dimensions of cells.
  

• Match Dimensions: Sets the grid position and resolution to match another grid file. The program will prompt for a grid file to get the position from. Certain commands require grids match position and resolution. Running this command will set that.
  
• Smooth Grid: Smoothing applies a quadratic smoothing algorithm to the grid by using neighboring nodes to adjust each grid node. This routine can be used to refine a grid so that the contours from the Contour from Grid routine appear smoother. Typically this adjustment is relatively small. To get more smoothing, run the routine more times.
• Plot Grid: This runs the Draw 3D Grid command. It is documented elsewhere in the manual.
  
• Export Grid: There are four choices for export options: Carlson CRD file, ASCII text as XYZ, ASII text as YXZ, and as a DTM format. There are two options for the ASCII delimiter, either a comma or a space. There is an option to skip a number of rows and columns between the exported points. When exporting as the Carlson CRD file, the description for the points is set below.
  


Export to DTM writes the current grid file to a DTM format text file. The format of this file is the following:

DTM 1.0         Header Line
test.dtm         Name of file
51                 Number of cells in X direction
51                 Number of cells in Y direction
79442.4697   Lower left grid corner Y coordinate
14899.0326   Lower left grid corner X coordinate
0.0                Lower left grid corner Z coordinate
11.5618         Dimension of cell in X direction
7.0639           Dimension of cell in Y direction
1581.2612     Grid cell values starting from lower left, moving from left to right
1580.8879
1580.3257
etc...


• Merge Grids: creates a grid file by merging together two existing grid files, grid1 and grid2. The current grid is grid1 and the program will prompt for a second grid. These two grids must overlap with the same location and resolution. The inclusion and exclusion perimeters apply to grid2 such that the merged grid will consist of grid2 cells within the inclusion perimeters and outside the exclusion perimeters and grid1 cells everywhere else. The result is stored in the current grid.
• Import Grid: There are 3 main formats that may be imported. They are from an ASCII file, from the program Surfer (both ASCII and Binary), and from a DEM (digital elevation model) such as from the USGS (US Geological Survey). The ASCII file can match various formats.

Import from ASCII File creates a grid file from X Y Z data in any text file. There does not need to be a current grid file loaded since this routine will create a grid file. The text file should consist of one X Y Z coordinate per row with the first coordinate being the lower left grid corner and the last coordinate as the upper right grid corner. There are options for space or comma separated coordinates and for the order of the coordinates as either row (left to right) or column (bottom to top). The prompting will be as follows:

Separation type [<Space>/Comma/FixedWidth]?
Column number for X coordinate <1>:
Column number for Y coordinate <2>:
Column number for Z value <3>:

• List Grid: displays a list of the northing, eastings and elevation of each grid corner. A grid corner will have no elevation, or Null value, listed as None, if the grid corner was outside the limits of the data during Make 3D Grid File.

• Spreadsheet: displays the grid elevations in a row and column spreadsheet that is in the same layout as the grid file. Grid elevations can be edited in this spreadsheet and saved upon exiting the spreadsheet.

• Select Grid(s): This is the first step to load a grid. Usually a grid needs to be loaded before running a function. If Batch Process Grids is turned on, then multiple grids may be selected while holding down the Shift or CTRL buttons.
  
• Grid Info: This function displays information about the grid file. It is a form of Grid Statistics. The items it displays are shown in the report below:

• Macro Command Recorder: If there is a GFU that is done over and over again, or for many different grids, then this Macro Recorder is an efficient way to perform Grid File Utilities on many files, for many functions.
  

When recording a step that involves another grid file, there are three options for storing this grid into the script. Use Grid Variable will use the grid assigned to the Grid Variable Name. Prompt for Grid File Name will bring up a grid file selection dialog each time the macro is run. Store the Grid File Name will save the specific grid file name into the macro.

To start the recording process, choose Record. Then go through the functions. Each will appear in the macro window. When done recording, choose Stop. The Append will add on to the end of an existing GFU file. Load will recall a save GFU file. Run will execute the Macro, and Edit will bring the text editor up for editing the GFU file. If Copy, Paste, Search and Replace are useful tools here. Sometimes it helps to record a function once, then copy and paste it many times while using the Search and Replace function to change grid file names etc.

• AutoExtrapolate On Load: This will extrapolate values for any null or empty values in the grid as the grid is loaded.
• Use Inclusion/Exclusion Areas: If this is turned on, then the GFU function will only be applied within the selected inclusion polyline and outside the selected exclusion polyline.
  
• Batch Process Grids: When this option is turned on, GFU functions can be executed on many grids at once. It is recommended to move the grids to a backup directory, or create a copy of them, as the grids are over-written with the same name. The functions that cannot be batched are: Plot Grid, Merge Grid, List Grid, Export Grid, Import Grid and Spreadsheet.
  

Pulldown Menu Location: Surface
Keyboard Command: GFU
Prerequisite: Make a grid (.GRD) file with the Make 3D Grid File command.
File Name: \lsp\makegrid.arx