> Well, one easy way to do what you want is to make several hundred
> ellipsoids spread along the axis of your shape, linearly changing from
> one shape to the next. This takes quite a few spheres to make a smooth
> shape, and has some obvious inefficiencies, but is quite feasible...in
> fact, it was a common way of creating swept shapes before the
> sphere_sweep primitive.

I'd thought of that but was afraid it'd be too inefficient.

> You can optimize it further by clipping of the
> inner spheres and heiarchial bounding. (Split the object in half, put
> each half in a nested union. Split each half in half, again putting the
> two halves in unions. Repeat...you end up with a heirarchial structure
> which removes most of the shapes from consideration early on in
> intersection testing.)

Ok... I'm very very new at RAY-Tracing and I'm not sure I
could follow that.  Are you saying built the object up my only
every taking the union of two shapes at a time.  Start by taking
the union of two ellipsoids.  Then taking the union of two of
those shapes and so on?  I don't know enough about how POV-Ray
works to see how that removes any of the shapes as each shape
will still form a part of the surface of the final shape.  Should merge
be used as I know it removes all the interior surfaces?  But I'm
still not sure why a merge of a merge would be faster then a
single merge.  I assume I'm missing something and my guess is
that its experience.  Would it be possible for you to post a
small piece of code that uses this "heiarchial bounding" so I
could study it and maybe get a better understanding of what
you are talking about?

Thanks,
Carl

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