On 26 Jul 1999 07:48:32 -0400, Nieminen Mika wrote:
>  (Everyone keeps saying that merge is (always) a lot slower than union,
>but no-one has ever said why. Or even proved it.)

If we look only at the time to calculate intersections, merge is slower
than union because it has to check each intersection to see if it's inside
another element.  Thus merge might be slower than union if you use a simple 
texture like "texture {pigment {color rgbt .8} finish{ambient .8}}" with no
or maybe only a single light source.

However, in the real world many of us use very complex textures with 
reflection and complex lighting.  Calculating the various patterns, and 
especially casting all those shadow rays and reflection rays, tends to dwarf 
the time it takes to test intersections for insideness.

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