Nieminen Juha wrote:
> 
> Ken <tyl### [at] pacbellnet> wrote:
> :   Not being a programmer I can only suggest that it might be useful in
> : csg operations - if the program had the ability to internally tessellate
> : primitives.
> 
>   Sorry, I didn't understand one thing:
> 
>   If we already have mathematically perfect objects, what's the point in
> tesselating it and then calculating subdivisions? AFAIK subdivision is done
> to approximate better the object the mesh is trying to represent, but we
> already have the mathematically perfect model. So what's the point?
>   And besides, couldn't it be done just by tesselating it with more accuracy?


  First I am really talking about adding two major processes here. The
first is the ability to internaly tessellate Pov primitives. The second
would be the addition of subdivision surfaces. The two together are a
powerful combination when applied in the correct circumstances.

  The point is that primitives are too perfect in some cases. Ever try
to make a realistic looking rock from a sphere primitive by applying a
normal to it ?

 I also think (and may be wrong) that with subdivision surfaces you can
create smooth curves between intersecting objects that would normally in
POV-Ray result only in perfect right angles. An example would be where
you had a cross shaped object. In Pov you would use two scaled boxes in
a union to create the cross. With subdivision you could also create a
radius where the intersecting surfaces meet. It is of course possible
to do this in Pov now but it requires several more csg operations to
get there.

There was a good example of this posted by Van Sickle when demonstrating
his Subdivision Surface Suite. He showed a crossing of two cylinders
before and after subdivision. In the final image the two cylinders
looked like they had been smoothly welded together with nice radiuses
in the corners.

Smoothing triangles with normals is not nearly as accurate or desirable
as have the ability to further tessellate an object mechanically. Another
benefit of adding subdivision surfaces.

And again I will point out that I am not saying primitives should be
replaced or that tessellating should be a default procedure. I would
like to see it as an optional process that could be turned on by the
user with a specific control function applied.

Also visit the site that Ron linked to. It is a good read.

-- 
Ken Tyler -  1300+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

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