Wasn't it pixelphile who wrote:
>Thanks for the ideas.  Your leisure time is well spent!
>It seems to me that the fact that three of the five points are identical
>means that my CAD program ought to use a triangle primitive instead of a
>polygon.  That way there will be no need to test for coplanarity, which it
>seems to me is _bound_ to fail due to rounding in some circumstances
>(except in the trivial cases of the points all lying on a single x, y or x
>plane).
>So I'll try to speak soothingly to the writer of the CAD program...

If the writer is amenable to suggestions, then try recommending the use
of mesh2 structures rather than individual polygons. POV doesn't have
this rounding error with meshes. Meshes render faster, use much less
memory and have smaller file sizes. Meshes also provide the ability to
handle extra features, like smoothness and uv_mapping.

I did some tests on a reasonably complicated model that I had in mesh2
format, by converting it to a set of polygons. In my case I had to scale
the thing up by a factor of 1000 to avoid the Singular Matrix problem.

I examined three cases:
        Mesh2
        Individual polygons each with their own "texture {soft_blue}"
        A union of polygons with a single texture

                mesh2           polygons        polygon union
                =====           ========        =============
File size       520,295         2,655,817       2,367,241
Parse time      2 secs          7 secs          6 secs
Render time     28 secs         37 secs         42 secs
Memory used     2,807,915       47,574,731      23,078,795


-- 
Mike Williams
Gentleman of Leisure

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