Subject:
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Re: Sphere tesselation
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Newsgroups:
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lugnet.cad.dev
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Date:
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Tue, 12 Sep 2000 19:06:39 GMT
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Viewed:
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1391 times
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"Steve Bliss" <steve.bliss@home.com> wrote in message
news:f5csrssq9rkotteig88soujitik82bkj48@4ax.com...
> In lugnet.cad.dev, Travis Cobbs wrote:
>
> > "Steve Bliss" <steve.bliss@home.com> wrote in message
> > news:ppnprssksi9anl3hi45qgq5kkbarndid1n@4ax.com...
> > > In lugnet.cad.dev, Travis Cobbs wrote:
> > >
> > > At some point, I'd like to replace the sphere p-files with something
> > > better-looking. Something like the 48\1-8sphe.dat I posted (see
> > > <http://news.lugnet.com/cad/dat/parts/primitives/?n=39>), but with only • 5
> > > vertices on each edge, to fit with the standard curved p-files.
> >
> > How did you generate this file? It certainly looks like it was
> > algorithmically generated. Don't tell me you figured out all those • points
> > BY HAND?
>
> It was a fractal-thingy--it started with a 10-vertex triangular mesh (the
> three points on the axes, two points along each edge, and the point at the
> center of the surface of the hemi-demi-semi-sphere). Then it divided each
> triangle in the mesh into 4 subtriangles. To figure the new points, it
> found the midpoint of each edge, and projected that point onto the surface
> of the unit sphere. These divisions were repeated for a specified number
> of iterations.
Thanks for the info. The next thing I'm going to try will be similar, but
iterative instead of recursive in order to allow for a set of points that's
not a power of 2 (which may or may not work). You had to make your starting
case overly complicated in order to handle 12, as explained below.
> I'm not sure why I started with the 10-mesh that I did. It would have • been
> a lot less code to start with just the 3 points on the axes. Maybe I
> wanted to have that center-point?
You had to, because 12 (the number of subdivisions along each edge) is not a
power of two, and since you could only cut the edge of each triangle in half
(subdividing it into 4 new triangles), you had to start with nine triangles
which could then be subdivided twice each to yield 9*n^4 total triangles,
where n is the number of subdivisions of those triangles, or 9*2^4=144
triangles.
--Travis Cobbs (tcobbs@san.REMOVE.rr.com)
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Message has 1 Reply:
 | | Re: Sphere tesselation
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| (...) I wonder if it's possible to push the (initial?) vertices toward the center. I was playing around with fractaling from a simplest case (1 triangle in the mesh). I noticed the center area was made up of one type of triangle (nearly (...) (26 years ago, 12-Sep-00, to lugnet.cad.dev)
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Message is in Reply To:
| | Re: Sphere tesselation
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| (...) It was a fractal-thingy--it started with a 10-vertex triangular mesh (the three points on the axes, two points along each edge, and the point at the center of the surface of the hemi-demi-semi-sphere). Then it divided each triangle in the mesh (...) (26 years ago, 12-Sep-00, to lugnet.cad.dev)
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