On Thu, 02 Dec 1999 19:27:01 -0500, Chris Huff wrote:
>I am working on a curvature pattern, inspired by the patina thread, 
>which would be for textures only(it would return a constant value if 
>used in media density). It would return a value depending on the amount 
>the surface the evaluation point is on is curving.

Given what you're trying to do, you only need the maximum curvature at 
that point.  Depending on direction of evaluation, the radius of 
curvature of the surface can vary from zero (a ridge) to infinity (a 
flat surface.)  A cube, for example, will have infinite radius of 
curvature everywhere on its faces, and the edges will have either 
zero or infinite radius of curvature depending on where your sample 
point falls.  The vertices will have zero radius of curvature in all
directions, ideally (though precision errors will give you infinite
radii for them, too.)

For the sake of determining accessibility, the smallest radius of 
curvature is the indicator: it doesn't matter that the surface is
perfectly flat in the X direction if it's so sharply curved in the 
Y direction that you can't get your cleaning implements into the 
groove.

Another consideration is that accessibility depends on which side 
of the surface you're looking at.  You can't clean the outside 
surface of that groove, because it's too narrow to fit your cleaning
tools, but you could clean the inside surface of the groove (i.e.
the other side of the sheet of metal) with any size tools, because
it bulges out from the surrounding surface.  This would generally
be handled by the texture map that's applied to the surface, but
your code may have to consider the possibility that surface normals 
might be inverted (i.e. pointing into the surface) which would cause 
some texturing wierdness.

-- 
These are my opinions.  I do NOT speak for the POV-Team.
The superpatch: http://www2.fwi.com/~parkerr/superpatch/
My other stuff: http://www2.fwi.com/~parkerr/traces.html

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