How can I rotate a grid 90° without switching the X and Y coordinates in Surfer?

Updated December 28, 2021 18:46

In some cases, you may wish to rotate the contents of a grid file (the Z values), without changing the actual XY values. This is useful if a grid file was created in another application (i.e. not Surfer) and the Z values were recorded in the grid file starting in a different corner than the lower left corner.

For example, say you have a grid file that created this map. The XYs are correct and in the correct orientation, but the Z values are rotated within the XY extents:

To rotate the Z value contents in a grid file 90° without interchanging the X and Y coordinates in Surfer, follow these steps:

Click Grids | Edit | Convert.
In the Open Grid dialog, select the grid file and click Open.
In the Save Grid As dialog, choose to save the grid as a GRD Surfer 6 Text Grid and click Save.
Click OK in the Export Options dialog.
Open the text grid in a text editor, like Notepad.
Switch the third and fourth rows.
1. Select the fourth row and click Edit | Cut.
2. Insert a new row after row 2.
3. Click Edit | Paste and paste the information as a new third row.
4. Delete the blank row
5. Click File | Save and save the changes. Close the file.
In Surfer, click Grids | Calculate | Transform.
In the Grid Transform dialog, click Browse in the Input Grid field.
Select the newly saved text grid and click Open.
In the Grid Transform dialog, choose Operation = Rotate and Angle = 90 (to rotate 90° counterclockwise) or 270 (to rotate 90° clockwise) and click OK.

contour map in Surfer showing rotated Z values but the same XY coordinates

Rotate the Z value contents in a grid file, while leaving the XY coordinates alone

Updated December, 2021

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