"Mike Williams" <nos### [at] econymdemoncouk> wrote in message
news:9eg### [at] econymdemoncouk...
> Wasn't it Captain Chemistry who wrote:
> >Hello everyone.
> >
> >I know this sounds extremely arrogant and I apologise if it doesn't do
the
> >same thing on anyone else's computer but you should check this out:
>
> It appears to be a bounding bug.
>
> If you switch bounding off, ("-MB" in the command line) then the POV
> results match what you'd expect from set theory. So the POV code doing
> the actual intersection, union and inversion code is working as you
> would expect ... snip ...

Hi Captain,
I think Mike has answered your main question about why bits of your shape
were missing,
but I think that POV is not doing quite what you think it is.

I'm not very familiar with set theory, but I suspect that the 'union' in set
theory combines both sets, whereas in POVRay it combines the two surfaces
(leaving internal surfaces in place). I think you probably want the POVRay
'merge' operation which creates a surface around the outside of the points
considered to be inside the object. You can see the difference if you add a
'clipped_by {plane{-z,0}}' to your CSG.

p.s.
In your left hand POVRay object you've transposed the intersection and merge
(and objects A and C), which seems to avoid the bounding bug. If you reverse
these to the form represented by your set description A ^ (C U B') you get
the same sort of problem as you had with your other two shapes.

Chris B.

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