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Re: fitting contours with ellipse [message #69341 is a reply to message #69338]

Tue, 05 January 2010 05:02

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Francis Burton writes:

> One requirement for a 'good fit' in this case is to have as
> much of the ellipse represented by data points as possible
> (i.e. no big gaps). The set of coordinates returned by CONTOUR
> using the PATH_INFO keyword should be well-spaced at least;
> whether there are enough coordinates will depend on the size
> of the contour path in relation to the grid spacing. I would
> simply feed the coordinates to the ellipse-fitting routine
> and see if it produces sensible results for your data.

Alas, the problem with the contours that come from
the contour command is that some of the time they
are NOT "well spaced". In fact, they are vectors.
So, if a contour segment is straight (say along an edge)
there will be no points at all between the ends
of the straight segment.

It was to get around this problem (among others) that
I wrote ArcSample, which samples a closed curve at
approximately equal intervals. It essentially
digitizes a contour line so you can do something
useful with it later. (I used it in my ActiveContour
program.)

http://www.dfanning.com/programs/arcsample.pro

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: fitting contours with ellipse By: fburton on Tue, 05 January 2010 07:55
		Re: fitting contours with ellipse By: David Fanning on Tue, 05 January 2010 05:02
		Re: fitting contours with ellipse By: fburton on Tue, 05 January 2010 03:22
		Re: fitting contours with ellipse By: natha on Fri, 08 January 2010 10:24

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