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In article <3a4e2a28@news.povray.org>, "Greg M. Johnson"
<"gregj;-)56590\""@aol.c;-)om> wrote:
> 1) Does anyone have code for making a mesh which is an icosahedron?
You might find something here:
http://www.swin.edu.au/astronomy/pbourke/
> 2) Does anyone have code for making a N-triangle approximation of a
> sphere (please don't code this just for me--does it already exist)?
Maybe you can find something useful in one of the discussions about
"evenly spaced points on a sphere" on these groups...
> 3) Say I'm going to put a few thousand spheres in a union, but then want
> to replace the spheres with meshes for memory's sake. How many
> triangles (I assume it's several thousand) does it take to cause the
> same memory usage/parse time as one sphere?
A single-triangle mesh will probably use more memory than a single
sphere, assuming texturing is the same. A copy of a mesh (of any size)
will probably use slightly less memory than a sphere, again with all
else equal.
For parse time, you will have to test it...but it would most likely be
less for a copy of a mesh than a sphere.
--
Christopher James Huff
Personal: chr### [at] mac com, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
<><
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Chris Huff wrote:
> > 2) Does anyone have code for making a N-triangle approximation of a
> > sphere (please don't code this just for me--does it already exist)?
>
> Maybe you can find something useful in one of the discussions about
> "evenly spaced points on a sphere" on these groups...
I've actually coded the scenario you described fairly successfully. The
problem comes in trying to figure out which of the points should be the
vertices of the triangles.
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I did one some weeks ago (of course in POV) ...
(just a try for myself) ...
I'll post it in p.b.s-f (If I find it again ...)
--
Jan Walzer
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> > > 2) Does anyone have code for making a N-triangle approximation of a
> > > sphere (please don't code this just for me--does it already exist)?
> >
> > Maybe you can find something useful in one of the discussions about
> > "evenly spaced points on a sphere" on these groups...
>
> I've actually coded the scenario you described fairly successfully. The
> problem comes in trying to figure out which of the points should be the
> vertices of the triangles.
I made some thoughts about this myself ...
It should be go with a recursive algorithm .... (sounds like StarTrek,
heheeee ...)
Imagine a regular tetraedron (ABCD),
with it's center (M),
having |A-M|=|B-M|=|C-M|=|D-M|=r
1) do for every triangle (ABC,ACD,ABD,BCD):
2) divide it into 4 regular triangles
3) normalize the distance of the 3 new points and the center (M) to r
4) go back to 1 until the sphere is fine enough ...
all clear ???
--
Jan Walzer
(currently no Signature)
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In article <3a4e6e6c$1@news.povray.org>, "Jan Walzer" <jan### [at] lzernet>
wrote:
> It should be go with a recursive algorithm .... (sounds like StarTrek,
> heheeee ...)
...snip...
That won't let you specify a specific number of triangles to use, only a
recursion level. The number of triangles increases rather rapidly with
recursion level.
--
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
<><
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"Greg M. Johnson" wrote:
> 1) Does anyone have code for making a mesh which is an icosahedron?
That reminds me, I was gonna unzip most of the source at my website...
http://davidf.faricy.net/source/meshpoly.inc
> 2) Does anyone have code for making a N-triangle approximation of a
> sphere (please don't code this just for me--does it already exist)?
I did this once, start with a regular polyhedron (tetra, octa or icosa will
work), subdivide each face into four triangles and normalize the vertices.
Recursive macro of course.
--
David Fontaine <dav### [at] faricynet> ICQ 55354965
My raytracing gallery: http://davidf.faricy.net/
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David Fontaine wrote:
> > 2) Does anyone have code for making a N-triangle approximation of a
> > sphere (please don't code this just for me--does it already exist)?
>
> I did this once, start with a regular polyhedron (tetra, octa or icosa will
> work), subdivide each face into four triangles and normalize the vertices.
> Recursive macro of course.
BTW I just thought of something, to use fewer triangles you could make the last
iteration subdivide into 2 or 3 instead.
--
David Fontaine <dav### [at] faricynet> ICQ 55354965
My raytracing gallery: http://davidf.faricy.net/
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Greg M. Johnson wrote:
> 2) Does anyone have code for making a N-triangle approximation of a
> sphere (please don't code this just for me--does it already exist)?
Uwe Zimmermann wrote a utility called "geodesic.inc" which
does this. I forget the URL but I know there is a pointer to it
from somewhere on the main povray site (the macros & include files
section). It's rather handy.
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"Greg M. Johnson" wrote:
>
> 1) Does anyone have code for making a mesh which is an icosahedron?
If you download my Surface Subdivision Suite at
http://users4.50megs.com/enphilistor/sss.htm
you should find therein code that will make you an icosahedron; it
can also subdivide it to make a smoother sphere.
Regards,
John
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On Sat, 30 Dec 2000 18:40:37 -0500, Chris Huff wrote:
>In article <3a4e6e6c$1@news.povray.org>, "Jan Walzer" <jan### [at] lzernet>
>wrote:
>
>> It should be go with a recursive algorithm .... (sounds like StarTrek,
>> heheeee ...)
>
>...snip...
>
>That won't let you specify a specific number of triangles to use, only a
>recursion level. The number of triangles increases rather rapidly with
>recursion level.
One way to provide more options is to also allow starting with a regular
octahedron or icosahedron.
My golfball code (at the address below) contains the germ of this algorithm
for a starting point of an icosahedron. It only generates the vertices,
not the triangles, but it might be a good starting point. I've been meaning
to generalize it a little (replace the constant #defines with a smaller number
of constant #defines) but I haven't gotten around to it yet.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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