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Re: Fitting an ROI to a distribution of points [message #47278]

Wed, 01 February 2006 09:24

Edd Edmondson
Messages: 50
Registered: January 2003

Member

David Fanning <davidf@dfanning.com> wrote:
> 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

After posting, I'd definitely take that fit_ellipse approach!

--
Edd

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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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