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How To: Calculate the maximum difference between a grid cell and it's neighbours

Summary

Using a 'kernal file' will restrict the analysis to the neighbours surrounding the cell currently being processed. Some simple mathematical evaluations will lead to the final result.

Procedure

  1. Create a text file (any_name.txt) with the following four lines:

       3 3
    1 1 1
    1 0 1
    1 1 1

    Make sure you type a return after the last number.

  2. Determine the maximum and and minimum values around the cell.

    Code:
    Grid: fmax = FOCALMAX (in_grd, IRREGULAR, donut.txt)
    Grid: fmin = FOCALMIN (in_grd, IRREGULAR, donut.txt)

  3. Determine the difference between the cell and the max/min values.

    Code:
    Grid: diffmax = ABS (fmax - in_grd)
    Grid: diffmin = ABS (in_grd - fmin)

  4. Assign the maximum difference to the output grid.

    Code:
    Grid: finaldiff = MAX (diffmax, diffmin)