When your XYZ data are collected or generated on regular intervals it is possible to produce a grid file that uses your values directly and does not interpolate the values for the grid nodes. You can use the Grid Data command to create a grid file in the correct format.
When you have a complete array of XYZ data (or a nearly complete set of data with only a few "holes"), you can use the Nearest Neighbor gridding method to convert your data directly to a grid file. The Nearest Neighbor method does not interpolate data but merely picks the closest point and assigns that value to the grid node.
To use the Home | Grid Data | Grid Data command to produce a .GRD grid file from regularly spaced data:
Create an XYZ data .DAT file from your data.
Select the Home | Grid Data | Grid Data command.
Specify the name of the XYZ data file in the Open dialog and click Open.
In the Grid Data dialog, select the Nearest Neighbor gridding method from the Gridding Method list. During gridding, the nearest Z value from the data file is assigned to the grid node.
Set the Spacing values in the Output Grid Geometry group to match the spacing of your data in the X and Y directions. This assures that the grid nodes coincide with your data. For example, if your data are separated by 100 meters over the extent of your map, enter 100 for the X Direction and Y Direction boxes.
Click OK in the Grid Data dialog and the grid file is created.
You can also produce grid files directly from an evenly spaced array of Z values. When your Z values are organized correctly in an ASCII file, you can use the file directly as a TXT Formatted Text Grid file. Alternatively, add some header information identifying the data as a grid file, specify the limits of the data, and then save the file. The ASCII grid file format is given in Surfer 6 Text Grid Format.