Hi Paul, here an example that may work for you: Define an area that is one and zero: yes? use coads_climatology yes? set region/ l=1 yes? let mask= if sst gt 15 then 1 else 0 Now define the left, lower, and right and upper derivative: yes? let myp = mask[y=@ddf] yes? let mxm = mask[x=@ddb] yes? let mym = mask[y=@ddb] Make a plot. If you are not familiar with the derivatives, please consult the manual. Now define the line, where the derivative is greater or smaller than 0: yes? let line = if mxp gt 0 or myp gt 0 or mxm lt 0 or mym lt 0 then 1 else 1/0 This is the result: yes? shade/l=1 mask yes? shade/over/l=1/pal=black line or yes? shade sst yes? shade/over/pal=black line May be this is a good starting point to play with modifications. Other schemes for corner points? Finally, in ferret there is a check whether or not a point is within a polygone. Please find details in the manual. Best, Martin Am 19.07.2016 um 19:17 schrieb Paul
Goddard:
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