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Re: Fitting an ROI to a distribution of points [message #47280 is a reply to message #47279]

Wed, 01 February 2006 09:14

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Olivia writes:

> I have a set of (x,y) coordinates which represent point-like galaxies
> in a galaxy cluster. Ultimately I want to describe the shape of the
> cluster as an ellipse, but I was planning on making some kind of blob
> first. I thought of gaussian smoothing, but I cannot work out how to
> get a filled in shape described by pixels to start working with. Does
> anyone have any ideas?

Here are a couple of articles describing techniques that you
might be able to use. The first describes how to create
a convex hull around a set of points. You could fill
in the polygon (convex hull) to create a blob of some
sort. The second describes how to calculate an ellipse
for a set of random points using a weighed average
approach.

http://www.dfanning.com/tips/convex_hull.html
http://www.dfanning.com/ip_tips/fit_ellipse.html

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Re: Fitting an ROI to a distribution of points By: Edd Edmondson on Wed, 01 February 2006 09:24
		Re: Fitting an ROI to a distribution of points By: Edd Edmondson on Wed, 01 February 2006 09:21
		Re: Fitting an ROI to a distribution of points By: David Fanning on Wed, 01 February 2006 09:14
		Re: Fitting an ROI to a distribution of points By: Olivia on Fri, 10 February 2006 07:42

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