[GRASS-user] distance from extent to origin cost surfaces

[Hamish]

Dylan:
> This is slightly incorrect -- as we are growing the cost surface to
> compute the perimeter, when we should be shrinking it. However it
> appears that r.grow cannot use a negative radius.

create a negative mask, grow that, then invert again:


r.mapcalc "inv_mask = if(isnull(mask), 1, null())"

r.grow in=inv_mask out=inv_mask.grown

r.mapcalc "mask_shrunk = if(isnull(inv_mask.grown), 1, null())"



Hamish




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