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Re: perimeter of a blob [message #18760 is a reply to message #18634]

Thu, 27 January 2000 00:00

Ben Tupper
Messages: 186
Registered: August 1999

Senior Member

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.

Thanks again!

Ben

--
Ben Tupper
Pemaquid River Company
248 Lower Round Pond Road
POB 106
Bristol, ME 04539

Tel: (207) 563-1048
Email: PemaquidRiver@tidewater.net

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[Message index]

		perimeter of a blob By: Ben Tupper on Wed, 26 January 2000 00:00
		Re: perimeter of a blob By: Ben Tupper on Thu, 27 January 2000 00:00
		Re: perimeter of a blob By: davidf on Thu, 27 January 2000 00:00
		Re: perimeter of a blob By: Richard Adams on Thu, 27 January 2000 00:00

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