William L. Baker
BakerWL at UWYO.EDU
Sat Jul 10 10:49:19 EDT 1999
Most shape indices (including perimeter/area) are measuring
boundary complexity to some extent, but are more a measure
of compactness. Perimeter/area has the undesirable trait
of varying with the size of the polygon even if polygon shape
remains constant, so it's not a good measure of
compactness/boundary complexity if polygons vary in size.
A better measure is either the corrected perim./area index
or the related circumscribing circle index. Both are in the
r.le programs which work with GRASS.
> -----Original Message-----
> From: Rich Shepard [SMTP:rshepard at appl-ecosys.com]
> Sent: Friday, July 09, 1999 11:56 PM
> To: grass at cecer.army.mil
> Subject: Re: Boundary shape
> On Thu, 8 Jul 1999, C.D.Lloyd wrote:
> > My colleague is looking for software that will characterise the
> > complexity of the boundary of an area. That is, if the boundary of an
> > area had very `wiggledy' complex edges then it would be distinct from an
> > area of which the edges were very smooth. The ultimate aim is to
> > describe and compare the shape of different boundaries of enclosed areas
> > derived from an interpretation of remotely-sensed imagery.
> The way we do it in ecology is to calculate the ratio of perimeter to
> area. The higher the number the more irregular the edge. You need to
> calibrate it for your purposes. Quick and easy to do. Even a spreadsheet
> will work.
> Dr. Richard B. Shepard, President
> Applied Ecosystem Services, Inc.
> 2404 SW 22nd Street
> Troutdale, OR 97060-1247 U.S.A.
> + 1 503-667-4517 (voice) | + 1 503-667-8863 (fax)
> rshepard at appl-ecosys.com
> Making environmentally-responsible mining happen.
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