Other couple questions that are related to this topic.  Here is a piece of
code from the CSG that I'm trying to optimize.

  #declare rear_tire = difference {
    sphere {<0, 85, 0>, 85 scale <1,1,.2>}
    union {
      cone {<0, 85, 20>, 50 <0, 85, -20>, 60}
      cone {<0, 85, -20>, 50 <0, 85, 20>, 60}
    }
    bounded_by { box {<-85,0, -13>, <85,170, 13>} }
  }

I can tell by viewing the bounding slabs with the +UD option that this has a
tighter bounding slab then it would if I didn't specify a bounded_by box.

First question: Why?  I did not use the -UR option and the documentation
says "To turn off the automatic removal of manual bounds you should specify
Remove_Bounds=off or use -UR. The default is Remove_Bounds=on."  Isn't the
above a manual bound?

Second question:  In terms of optimization does it make any difference if
the above union is replaced with a merge?  I also just now spotted this line
in the documentation "The CSG difference operation takes the intersection
between the first object and the inverse of all subsequent objects."  I just
verified that the above union statement isn't even needed. Would removing it
cause it to render faster?  Its a little easier for me to follow the code if
I leave it in there.

Thanks,
Carl

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