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Re: Polygon hull [message #22994 is a reply to message #22993]

Mon, 18 December 2000 15:47

Mark Hadfield
Messages: 783
Registered: May 1995

Senior Member

"Barbara A Cohen" <bcohen@lpl.arizona.edu> wrote in message
news:91jchs$ep4$1@news.ccit.arizona.edu...
> Hi, I have an array of data and I want to plot a polygon that encompasses
> all the points within it. I have tried JHU's convexhull but it fails to
> encompass all the data (example below). Does anyone else have a program
> to do this?

I've just been reading through my brand new copy of David Fanning's "IDL
Programming Techniques 2nd Edition" and I came across the following, in a
discussion of Delaunay triangulation:

"Note that you can return the convex hull of these points with the
TRIANGULATE command too. Simply add a fourth argument to the command...and
the points on the parameter [huh? must be perimeter] of this set of points
will be returned to you."

Here's an example:

x=[0.36,0.35,0.39,0.42,0.60,0.41,0.48,0.73,0.46,0.42,0.42,0. 42,0.47,0.44,0.4
7,0.49,0.54,0.64,0.65]
y=[0.19,0.26,0.26,0.26,0.14,0.22,0.15,0.10,0.16,0.30,0.27,0. 27,0.23,0.23,0.2
2,0.16,0.16,0.08,0.08]

plot, x, y, color=0, /nodata

triangulate, x, y, triangles, b

polyfill, x[b], y[b], color=150, fill_pattern=50

plot, x, y, psym=7, color=0

---
Mark Hadfield
m.hadfield@niwa.cri.nz http://katipo.niwa.cri.nz/~hadfield/
National Institute for Water and Atmospheric Research
PO Box 14-901, Wellington, New Zealand

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[Message index]

		Re: Polygon hull By: davidf on Thu, 21 December 2000 12:04
		Re: Polygon hull By: Pavel A. Romashkin on Thu, 21 December 2000 11:14
		Re: Polygon hull By: bcohen on Tue, 19 December 2000 05:48
		Re: Polygon hull By: davidf on Mon, 18 December 2000 16:25
		Re: Polygon hull By: Mark Hadfield on Mon, 18 December 2000 15:47
		Re: Polygon hull By: bcohen on Mon, 18 December 2000 13:48
		Re: Polygon hull By: cjengo on Mon, 18 December 2000 04:18
		Re: Polygon hull By: davidf on Sun, 17 December 2000 15:57

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