Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
Kenneth P. Bowman (bowman@null.tamu.edu) writes: > I think that TRIANGULATE returns the convex hull of a set of points. If > the boundary of the region is concave, the perimeter is different from the > perimeter of the convex hull. Ah, yes. Now I remember why I haven't yet written that article. :-) Cheers, David -- David Fanning, Ph.D. Fanning Software Consulting Phone: 970-221-0438 E-Mail: davidf@dfanning.com Coyote's Guide to IDL Programming: http://www.dfanning.com/ Toll-Free IDL Book Orders: 1-888-461-0155
In article <MPG.12f91c174956d2d89899fc@news.frii.com>, davidf@dfanning.com (David Fanning) wrote: > Anyway, the easiest way to get a perimeter, I think is to > use the Triangulate function. > > Cheers, I think that TRIANGULATE returns the convex hull of a set of points. If the boundary of the region is concave, the perimeter is different from the perimeter of the convex hull. Ken Bowman
Ben Tupper (tupper@seadas.bigelow.org) writes: > I am looking for an efficient means of finding the perimeter of > contiguous blobs of pixels within an image. These blobs are the > regions returned by the LABEL_REGION function. I have been using the > trusty brute-force-and-ignorance appraoch where I scan rows and columns > within each blob, recording the min and max coordinates of each > row/column. It is a cumbersome task and leaves gaps in certain areas > (especially concavities in the blob.) I don't know why I haven't written an article about this, since this is about the 10th time I've needed to look this up, but maybe I will. :-) Anyway, the easiest way to get a perimeter, I think is to use the Triangulate function. An optional fourth positional parameter returns the perimeter points. You will probably have to figure out how to get the 2D indices from the 1D array of indices returned by Label_Region, but *that* is on my web page for sure: http://www.dfanning.com/tips/where_to_2d.html IDL> Triangulate, xpts, ypts, tri, boundaryPts Cheers, David -- David Fanning, Ph.D. Fanning Software Consulting Phone: 970-221-0438 E-Mail: davidf@dfanning.com Coyote's Guide to IDL Programming: http://www.dfanning.com/ Toll-Free IDL Book Orders: 1-888-461-0155