In Surfer 22 and newer, this is no longer an issue as you can choose how the grids aligned. See Surfer's Help for more information on the Align Grids field.
In Surfer 21 and previous, while viewing the Grid Math or Grid Volume dialog, you can select a grid and click on the Grid Info button to get information about the grid, including the grid size (the number of rows and columns) and the X and Y extents.
You can correct this problem by changing one grid to match the XY extents and grid size of the other grid. You can do this a couple different ways:
Method 1: If you have the original XYZ data, you can regrid one (or both) of the grids by:
- Clicking Home | Grid Data | Grid Data.
- In the Grid Data - Select Data dialog, click Browse and select the data file, or, if the data file is open, click None and select the file. Ensure the X, Y, Z columns are assigned correctly.
- Click Skip to End
- On the Grid Data - <gridding method> - Output dialog, click None next to Copy geometry from and either select an open grid whose extents you'd like to match from the list, or click Browse to browse to a grid file.
- In Surfer 15 and previous, you will need to manually specify the # of Nodes, the Minimum, and the Maximum in the X and Y directions (X is columns, Y is rows) so it matches that of the other grid.
- Click OK to create the grid.
Method 2: You can resample one or both grids using the Grids | Resize | Mosaic command:
- Click Grids | Resize | Mosaic, select one of the grid files and click Open.
- In the Grid Mosaic dialog, specify the # of Nodes, the Minimum, and the Maximum in the X and Y directions (X is columns, Y is rows) so it matches that of the other grid.
- Click OK to create the grid
Once the two grid files match in XY extents and grid size, then you can use them together in Grid Math or Grid Volume.
Updated November 26, 2019