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Wasn't it Christopher James Huff who wrote:
>Vertex normals aren't perfect in all situations either. Consider a cone
>formed of a fan of triangles. Each triangle has only one vertex at the
>point of the cone. You will have as many normals as triangles at that
>point, and no interpolation between them...
There's no reason why a mesh can't have several vertices at a single
point in space. Modelling programs split vertices at places where
there's a discontinuity in the normals (like where the side of the cone
meets the base) and the same thing can be done for the apex of the cone.
If the cone mesh is uv-mapped, then the apex point has to be split into
multiple vertices anyway.
I had a quick look at a cone object generated by Poser5, and it turns
out that the vertices at the point of the cone aren't exactly
coincident. What it appears to so is take a cylinder and shrink one end
until it's *almost* a point. It actually uses 4-sided polygons for the
surface. Each polygon has two vertices on the base and two vertices at
the apex of the cone.
--
Mike Williams
Gentleman of Leisure
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In article <uCVIPAAGvl7$EwpE@econym.demon.co.uk>,
Mike Williams <nos### [at] econym demoncouk> wrote:
> There's no reason why a mesh can't have several vertices at a single
> point in space. Modelling programs split vertices at places where
> there's a discontinuity in the normals (like where the side of the cone
> meets the base) and the same thing can be done for the apex of the cone.
I don't think you understood what I said. Each triangle has only one
corner at the point of the cone, and one normal for that point. This
makes it impossible to properly interpolate the normals. It would need
for the cone-point vertex of each triangle to have *two* normals, one
associated with each edge of the triangle, and for normals to be
interpolated between the edges rather than the corners. Essentially a
quad with one side zero-length.
> I had a quick look at a cone object generated by Poser5, and it turns
> out that the vertices at the point of the cone aren't exactly
> coincident. What it appears to so is take a cylinder and shrink one end
> until it's *almost* a point. It actually uses 4-sided polygons for the
> surface. Each polygon has two vertices on the base and two vertices at
> the apex of the cone.
Right, that's what you have to do if you want smooth normals on a cone.
You can still put the point on, if it's small enough that the normal
transitions are unnoticeable and still large enough to matter, but it
adds a lot of triangles to the cone for very little benefit.
--
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/
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On Tue, 23 Dec 2003 19:22:10 +0100, Fabien Mosen <fab### [at] skynetbe>
wrote:
> POV-Ray was never intended to be used in production.
> [...]
> POV-Ray has it's own "personality"
On the other hand thinking about "production" as "high quality art" and
observing quality of average image nowadays and 5 years ago in
povray.binaries.images I think POV-Ray's personality allows it to be used in
production succesfuly. I can easy imagine book, pictures in art-museum,
decorations and illustartions in newspaper made only with POV-Ray. Every tool
has its masters and its newbies.
ABX
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