In article <uCVIPAAGvl7$EwpE@econym.demon.co.uk>,
 Mike Williams <nos### [at] econymdemoncouk> 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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