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Re: Need Some Good Ideas [message #29440 is a reply to message #29439]

Wed, 20 February 2002 23:02

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

Hey David--

Interesting problem! The first thing that comes to mind is to try to
smooth the data somewhat. For example, by fitting a spline through it
(SPL_INIT), and then interpolating the spline onto a much finer grid
(SPL_INTERP).

Now, that doesn't totally solve your problem, because the interpolants
will still be irregularly spaced, but they will be much more finely
sampled. You could then sum them to get an arc-length over each
segment, and then resample after adjusting for the arc length.

Do you have some example data?

Craig

David Fanning <david@dfanning.com> writes:
> Folks,
>
> Do you have your thinking caps on? I'm looking for
> a few good ideas.
>
> I have a bunch of blobs. (Think spots on the
> Gateway cow.) I would like to analyze the curvature
> and bends in the perimeter of the blobs. I have
> the indices of the points that make up the blob, and
> I have obtained the "perimeter" points by contouring
> the blob. Unfortunately, these perimeter points are
> not evenly distributed. (Think of a blob that has a
> long, straight side. The contour command will put a
> point at either end of the straight bit, so the points
> on that side of the blob are sparse, while the points
> along a tight bend on the other side of the blob
> are dense.)
>
> I say "unfortunately" because we have a method that
> uses the derivative of the perimeter at each point
> and the FFT transform of the derivative distribution,
> but it seems to be giving funny results because of this
> point distribution problem.
>
> Has anyone heard of this kind of curvature analysis
> before? Any pointers to literature? I've heard that
> IDL can be used to solve these kinds of problems. :-)
>
> Thanks,
>
> David
> --
> David W. Fanning, Ph.D.
> Fanning Software Consulting
> Phone: 970-221-0438, E-mail: david@dfanning.com
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Toll-Free IDL Book Orders: 1-888-461-0155

--
------------------------------------------------------------ --------------
Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
------------------------------------------------------------ --------------

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[Message index]

		Re: Need Some Good Ideas By: btupper on Thu, 21 February 2002 14:35
		Re: Need Some Good Ideas By: Martin Downing on Thu, 21 February 2002 14:35
		Re: Need Some Good Ideas By: David Fanning on Thu, 21 February 2002 11:22
		Re: Need Some Good Ideas By: btupper on Thu, 21 February 2002 10:43
		Re: Need Some Good Ideas By: David Fanning on Thu, 21 February 2002 08:09
		Re: Need Some Good Ideas By: David Fanning on Thu, 21 February 2002 07:50
		Re: Need Some Good Ideas By: dw on Thu, 21 February 2002 07:22
		Re: Need Some Good Ideas By: ronn on Thu, 21 February 2002 04:46
		Re: Need Some Good Ideas By: Craig Markwardt on Wed, 20 February 2002 23:46
		Re: Need Some Good Ideas By: Craig Markwardt on Wed, 20 February 2002 23:02
		Re: Need Some Good Ideas By: Stein Vidar Hagfors H[1] on Fri, 22 February 2002 09:05

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