"Sampsonite! I was way off."

Now I get it.  Thanks alot for the explanation Ken.
		
		Kyle

Ken wrote:
> 
> 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

Post a reply to this message