Calculating the default Grid Spacing or # of Nodes in the Grid Data dialog in Surfer

The default grid resolution is defined by either the grid Spacing or the # of Nodes in the Output Grid Geometry section, in the Output page of the Grid Data dialog.

These fields are calculated as follows:
  1. 100 grid nodes are assigned to the longest direction.
  2. The grid Spacing for the longest direction is then calculated:
         (Maximum-Minimum) / (# of Nodes – 1)
  3. The same grid Spacing (or as close to it as possible) is applied to the shorter direction.
  4. The # of Nodes for the shortest direction is calculated:
         ((Maximum-Minimum) / Spacing) + 1

Note: If the # of Nodes in the shorter direction is not greater than 4, then the Minimum and Maximum values in that direction will be adjusted so that there are at least 4 grid nodes. This means that for data sets where one direction has a vastly different range than the other direction, the grid extents in the shorter direction may not exactly match the extents in the original data.


Updated March 2024

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