CGAL users discussion list

[Matthias Baas <>]

Hi,

recently I was playing around with doing CSG operations with Nef
polyhedra which, after some initial hiccups, works quite well so far.
But there's one case where I don't get the results that I would have
expected and that's when I do a CSG operation with an object that is
"hollow". I was creating a cube and a slightly smaller cube whose
faces have a different orientation and merged the two (or think of
taking the difference of a solid cube and a slightly smaller solid
cube). My expectation would have been that this describes a hollow
cube but with walls that have some thickness. But when I do an
intersection with another solid cube that partially overlaps the
hollow cube then the result is as if both cubes were solid whereas I
would have expected to just get a part of the walls.
But when I create a little hole somewhere in that hollow cube (so that
from the outside you could get into the inside just by walking along
the surface), then the above CSG operation works as expected.

Now my question just is, is this hollow cube representation a valid
input for the CSG algorithm which is supposed to work or is this an
invalid object? (the is_valid() method on the Nef polyhedron returned
true though)

Thanks,

- Matthias -