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Re: perimeter of a blob
Thanks to each of you for your help.
I have tried the convolution and contouring methods suggested by Richard
and David respectively. I used a black (0) and white (255) image of the
capital letter G (hand drawn.)
The convolution exactly defines the inclusive perimeter of the blob. I
haven't figured out how to sort the indicies into a clockwise (or
counter clockwise order yet... but I haven't tried either.)
The contour method misses the exact inclusive perimeter whenever an
inside corner is encountered (i.e. concavity.) It cuts diagonally
across these inside corners a result. The loss is nearly insignificant
in this case, but I recall have difficulty comparing polygon perimeter
estimates made in IDL with those made on the same data in ARC/INFO.
Each method works for my current purposes.
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