Wasn't it Andrea Ryan who wrote:
>> Of course this only works if you can come up with a fairly good bounding
>> box manually - perhaps not terribly hard for polyhedra, if you know your
>> trigonometry.
>
>Should bounded boxes be manually added to polyhedra if they are meshes?
>Brendan

It's not necessary. POV can easily determine a sensible automatic
bounding box for meshes just by looking for the vertex that has the min
and max values in each of the three directions.

Manual bounding boxes are only a good idea if you happen to know
something about the way that your differences or intersections reduce
the size of a surface. POV sets automatic bounds that include the whole
of every component that's involved in the difference or intersection. We
might happen to know that the intersection is much smaller than the
things that are intersecting.

In the case of the polyhedra in shapes2.inc the things that are
intersecting are infinite planes so POV sets the bounds to infinity
(i.e. no bounding box), but we happen to know that the intersection of
these planes is a finite shape and can apply smaller manual bounds.

-- 
Mike Williams
Gentleman of Leisure

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