Achill wrote:
> 
> [...]
> 
> Well, ok.
> A concrete example would be the sum of the tetrahedron T with vertices
> <0,0,0>, <1,0,0>, <0,1,0> and <0,0,1> with "its negative" -T with
> vertices <0,0,0>, <-1,0,0>, <0,-1,0> and <0,0,-1>.
> The outcome is a polyhedron (polytope) with vertices
> <-1, 0, 0>, <0, -1, 0>, <0, 0, -1>, <1, 0, 0>, <1, -1, 0>, <1, 0, -1>,
> <0, 1, 0>, <-1, 1, 0>, <0, 1, -1>, <0, 0, 1>, <-1, 0, 1>, <0, -1, 1>.
> 
> Generally, such vector sums of polytopes can be evaluated for example
> with the program "polymake" (www.math.tu-berlin.de/polymake/)

Well, so much for polyhedra - you can surely create any polyhedron you
want with meshes.  

> > Let's say we have a unit cube between <0,0,0> and <1,1,1> and a sphere at
> > <0,0,0> with radius 1.  What is the 'vector sum' of these objects?
> 
> As far as I understand the macro
> "Round_Box_Union(PtA, PtB, EdgeRadius)",
> it would be "Round_Box_Union(<0,0,0>, <1,1,1>, 1)".

So the vector sum of an arbitrary surface and a sphere at <0,0,0> with
radius 1 is the same as with any other sphere with the radius 1?  Sounds
strange.  Furthermore this means that this sum is not commutative.  

Christoph

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