Grid Data - Output (XYZC Data)
The Output page in the Grid Data dialog includes output options for the grid file, including geometry, data limits and transforms, and generating a report.
Specify grid file output options in the Output page.
Output Grid Geometry
The Copy geometry from option copies the grid geometry from an existing map layer or grid file. This option is useful if you have many grids that you'd like to all use the same geometry.
To copy the geometry from an existing layer, select the layer in the Copy geometry from list. To copy the geometry from a grid file, click Browse and select the file in the Open Grid dialog. Select <None> to return the Output Grid Geometry options to their default values and to manually edit the grid geometry.
Grid limits are the minimum and maximum X, Y, and Z coordinates for the 3Dgrid. Surfer computes the minimum and maximum X, Y, and Z values from the XYZC data file. These values are used as the default minimum and maximum coordinates for the grid.
Grid limits define the X, Y, and Z extents of the output grid. The extents of the grid define the extents of contour maps, color relief maps, shaded relief maps, vector maps, 3D wireframes, and 3D surfaces created from grid files. When creating a grid file, you can set the grid limits to the X, Y, and Z extents you want to use for your map. Once a grid file is created, you cannot produce a grid-based map larger than the extent of the grid file. If you find you need larger grid limits, you must regrid the data. You can, however, read in a subset of the grid file to produce a map smaller than the extent of the grid file.
When either the X, Y, or Z value is in a date/time format, the date/time values are converted and stored in the grid as numbers.
Grid density is a measure of the number of grid nodes in the grid. The direction (X Direction, Y Direction, or (Z Direction) that covers the greater extent (the greater number of data units) is assigned 100 grid nodes by default. The number of grid nodes in the other directions are computed so that the grid nodes Spacing in the three directions are as close to one another as possible.
By defining the grid limits and the number of rows and columns, the Spacing values are automatically determined as the distance in data units between adjacent rows and adjacent columns.
Note on High Density Grid Files
Higher grid densities (smaller Spacing and a larger # of Nodes) increase the smoothness in grid-based maps. However, an increase in the number of grid nodes proportionally increases the gridding time, drawing time, and the grid file size. You can have up to 2,147,483,647 rows and columns in a grid file. It is likely your computer will run out of memory before reaching the maximum grid size. The primary use for the large grid size maximum is to allow grids with extreme aspect ratios to be created.
More information on grid file density can be found here.
Grid C Limits
In some cases, the gridding interpolation and extrapolation can result in undesired values, for example negative numbers in cases where negative values are physically impossible. The Grid C Limits options clamp the grid output to specific minimum and maximum values.
The Grid C Limits are applied after the interpolation operation. After the grid interpolation is performed, Surfer locates any grid values less than the Minimum and replaces them with the Data min or Custom value. Surfer locates any grid values greater than the Maximum and replaces them with the Data max or Custom value.
To clamp the output to a specific minimum value, click the current selection next to Minimum, and select None, Data min, or Custom from the list. If Data min is selected, the data minimum will be displayed in the field to the right of the Minimum list. Select Custom and type a value in the input box to use a user-defined Minimum.
To clamp the output to a specific maximum value, click the current selection next to Maximum, and select None, Data max, or Custom from the list. If Data max is selected, the data maximum will be displayed in the field to the right of the Maximum list. Select Custom and type a value in the input box to use a user-defined Maximum.
The C Transform option changes how the C values are gridded. Available options are Linear; Log, save as log; and Log, save as linear. To change the C Transform option, click on the existing option and select the desired option from the list.
Linear uses the C values in the worksheet for gridding. No transformation is applied to the C values. The Linear method is a good option for data that gradually increases over space. This is the default C Transform.
Both Log options use take the log (base 10) of the C values before gridding. The log (base 10) of the C value is then used for gridding. The Log, save as log takes the log (base 10) of the C values and uses the log value for gridding. The grid is then saved with the log (base 10) values. The Log, save as linear takes the log (base 10) of the C values and uses the log value for gridding. The grid is then converted back to the linear C values by taking the antilog of the gridded results. When Log, save as log or Log, save as linear is selected, at least three data points must be positive C values. Negative values are ignored for gridding. Both Log methods are good options when the data changes very quickly over a small area or when very high and very low values occur very closely to each other. This can be common with concentration values in ground water or geochemical data.
The images above display the difference in gridding the posted data with linear (top right) and log (bottom contours). The log contours on bottom show the difference in C values between the grid when Log, save as log (bottom left) and Log, save as linear (bottom right) are selected.
Choose a path and file name for the grid file in the Output Grid group. You can type a path and file name, or click the button to browse to a new path and enter a file name in the Save Grid As dialog.
Check the box next to the Grid Report option to create a gridding report that includes all the gridding parameters used to generate a grid. This report also includes statistics about the grid. You can also access the grid statistics by creating a grid information report. Create a grid information report in the Grid Editor by clicking the Grid Editor | Options | Grid Info command or by clicking the Grids | Info | Grid Info command from any document window.
Add New Map or Layer
Check the Add grid as layer to check box to automatically add the created grid to a new or existing map. Select [New Map] in the Add grid as layer to field to create a new map. Click the current selection and select an existing map to add a new layer to the map. Select the layer type by clicking the current selection in the New layer type field and selecting the desired layer type from the list.
Click Save Settings to save the current Grid Data dialog settings from all dialog pages (Select Data, Options, and Output) to a Grid Data Settings file. Grid Data Settings files can be loaded on the Select Data page when creating grids.
Click Finish to create the grid file, or click Back to return to previous dialog pages.