Grid files are necessary in Surfer to create grid-based maps types. Data files are typically randomly spaced files, and this data must be converted into an evenly spaced grid before using many of Surfer's features. Grid files are produced from XYZ/XYZC data using the Home | Grid Data | Grid Data, the button, or the Grids | New Grid | Grid Data command. With this command, you can specify the parameters for the particular gridding method and the extents of the grid. The gridding methods define the way in which the data are interpolated when producing a grid file.
Data files should be arranged with all X data in one column, all Y data in another column, and all Z data in a third column. If gridding XYZC data, all C data should be in another column. Each data column can be any column in the data file and in any order. The columns are selected in the Select Data page.
When creating a grid file you can usually accept all of the default gridding parameters and generate a grid file that represents your data well. Under most circumstances, the recommended gridding method is kriging with the default linear variogram. This is the selected default gridding method because it gives good results for most XYZ data sets.
There are several gridding parameters you can set when producing a grid file. Refer to the gridding method for more information on specific parameters. Most gridding methods require at least three non-collinear data points. The Inverse Distance, Nearest Neighbor, Moving Average, and Data Metrics methods require at least three data points, collinear or not. Some methods require more data points. For example, a higher-order polynomial fit needs more than three data points; there must be at least as many data as there are degrees of freedom. When the Z Transform is set to Log, save as log or Log, save as linear, at least three data points must contain Z values that are non-negative and non-zero. Click the Grids | New Grid | Grid Data or Home | Grid Data | Grid Data command to choose the data to be used in the gridding process.
Grid Data Dialog
Click the Grids | New Grid | Grid Data or Home | Grid Data | Grid Data command to display the Grid Data dialog. The Grid Data dialog includes multiple pages:
Choosing a Gridding Method Based on the Number of XYZ Data Points
General Gridding Recommendations