.grd file extension

The RockWorks program uses the GRD file extension to store regularly spaced XYG data for use in contour maps and 3D surfaces in an ASCII format. "XYG" indicates that the dependent variable could be anything and not just the Z value typically associated with depth or elevation. The "G" originally meant the grade or value of concentration of ore in rock, but has been extended to mean any variable.

The first line lists the X-coordinate of the westernmost grid node.
The second line lists the Y-coordinate of the southernmost grid node.
The third line lists the number of cells (nodes - 1) that are listed for the X-axis (west to east), and the fourth lists the number of cells listed for the Y-axis (south to north).
The fifth and sixth lines list the spacing, in map units, of the grid nodes along the X-axis and Y-axis, respectively.
Starting in the seventh line, the Z-values for the grid nodes are listed, starting with the grid node in the southwestern corner of the grid and proceeding to the north. When the top of that first column of nodes is reached, the listing proceeds with the second column, starting with the southernmost node and listing upward. A Z-value will be listed for each node in the GRD file.

4.10000000000000E+0001
1.53000000000000E+0002
50
49
5.54000000000087E+0000
5.54000000000087E+0000
3.78120173233096E+0002
3.79369176873937E+0002
3.80618180514313E+0002
3.81867184155155E+0002
3.83116187795997E+0002
3.84365191436838E+0002
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