Am 16.07.2016 um 15:28 schrieb Dave Blandston:

> So if you can fix POV-Ray's min_extent () and max_extent () functions to work
> with CSG intersections or think of a work-around, here's a macro to compute
> kerning values. Good luck!

Talking of "fixing" the functions is a bit off the mark: They're not
broken; they're specified to give you the coordinates of the bounding
box, and that's exactly what they do. The auto-computed bounding boxes,
in turn, do not have to be perfect -- and for fundamental reasons cannot
be. All that's necessary for bounding boxes is that they are guaranteed
to include the entire object, while still being reasonably small.

Given the vast palette of geometric primitives supported by POV-Ray,
computing the exact extensions of an arbitrary CSG intersection or
difference is in fact a "hard problem" -- in the technical sense as used
in informatics. Meaning "practically impossible".

Algorithms to compute approximations are feasible, but come with the
risk of giving erroneous results, computing dimensions that fail to
include the entire object, which is a no-go for bounding boxes.

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