Surfer can use the polynomial regression gridding method to calculate a grid file representing the trend of a surface, and then you can use Grid Math to remove that trend from your original grid file.
To remove a first or second order trend surface from a grid file, follow these steps:
- Click Home | Grid Data | Grid Data, select your data file and click Open.
- Select your desired gridding method and options. Note the Minimum, Maximum, and # of Nodes in the X and Y directions, and click OK.
- Click Home | Grid Data | Grid Data again, select your data file again and click Open.
- This time, select the Polynomial Regression gridding method.
- Click the Advanced Options button, specify the order of the trend surface and click OK.
- Make sure the Grid Line Geometry section has the same Minimum, Maximum, and # of Nodes in the X and Y directions as your original grid file.
- Specify a new grid file name and click OK.
- Click Grids | Calculate | Math.
- In the Grid Math dialog, click the Add Grids button.
- Select both grids and click Open.
- Make sure the original grid has the variable A and the polynomial regression grid has the variable B.
- Click the yellow Change Filename icon to the right of Output Grid, and specify a new grid file name and location and click Save.
- Enter the function A - B and click OK. The new grid file will be the original data minus the trend.
Updated October 16, 2018