Kyle wrote:
> 
> I've been wondering the same thing.  This is my interpretation.... If
> you put a bounding box around an object, when POV-Ray parses the scene,
> it uses the boxes to determine if the enclosed object is visible in the
> scene. If not, it will not include the object, thus reducing memory
> consumption.  Like i said, I really don't know for sure so I wouldn't
> trust a word of what I wrote above.  I'm curious to know what it is
> exactly.
>                 Kyle

  That is not quite correct. Think of it this way. A box has 6 faces and
12 edges. When pov shoots rays in to the scene to see what they rays strike
it will have to account for the bouncing of the rays from the different
faces and edges that the rays encounter. When you have multiple objects
used in a csg operation, the objects, even though some of the edges are
missing from being in a csg, are still intact from the point of view of
the ray calculation process. What the bounding box does is confine the
shape of the object as a single entity instead of a group of objects
joined together. This speeds up rendering because it doesn't have to
calculate all of the interior edges that have been removed by the csg
operation. In other words it's no longer a group of primitives it is a
new primitive with a unique shape.

  As to whether this may be allowed with media and if it would make a
difference is something of a different matter. I just did a simple test
using one of the example files that comes with Pov and it took 2 sec.
longer with a bounding object. It appears that the benefits are 0.
The extra two second were probably the added time it took to issue the
warning that the sphere I bounded was unnecessarily bounded.
-- 
Ken Tyler

mailto://tylereng@pacbell.net

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