One example of a CSG that should be manually bound is a brick wall. If you
have a scene with a significant portion of the backgroup a brick wall (made
up of many boxes, for example) then POV will check each box for every ray.
Although POV will make bounds for the whole wall the bounding box will
sorround the whole wall and not help at all.

One way to make more effecient bounds for such a shape is something like a
box shaped bounding box around each row of bricks. If the brick wall is 40
rows high and 20 bricks wide and you make a bound for each row then each ray
will check those 40 bounds first and then the 20 bricks within it instead of
the total 800 bricks, a significant savings.

--Rainer

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