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| Re: 3D envelope surface around data points? [message #19456 is a reply to message #19396] |
Thu, 23 March 2000 00:00  |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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Eric Williams wrote:
>
> I was wondering if there was a way to take a set of data points (stars
> in a galaxy) that define an outer surface in 3 dimensions, and draw a
> surface that envelopes and includes the points. I haven't done much
> multi-dimensional plots in IDL so any tips and hints for trying this
> would be helpful.
What you're asking for is called the "convex hull" of a set of points.
This is a famous difficult problem. There's a fairly straightforward
algorithm that's very slow (O(N^3), IIRC), and no known algorithm that's
much faster than the straightforward one.
I found a downloadable library
<http://www.ee.byu.edu/~wilde/polyhedra.html> for dealing with
polyhedra, that is said to contain C code for a convex hull function.
I've no idea if it's any good, or even if it's what it seems to be, but
you could try translating it into IDL.
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