CGAL users discussion list

["Aviv Hurvitz" <>]

Hi Fred,

Thanks. Knowing it is possible is important. My next step will be to see how well it performs, and if I get the performance I want I'll move to CGAL and do the marking thing you did.

BTW I should say that I'm working with triangle meshes and that I don't expect to see degenerate configurations (faces or edges) since the surface approximates a natural (not synthetic) object, and therefore co-planar edges are unlikely. This suggests that CGAL is "overkill" for this task - much more sophisticated than what I need. I considered trying to use a program like Autocad/3D studio/Blender for this computation. Have you had any experience with other libraries?

- Aviv

On Sat, Dec 27, 2008 at 7:10 PM, <> wrote:

> I have two closed solids bounded by triangle meshes, call them A and B.
> First, I'd like to cut one with the other, i.e. compute C=A-B. The result
> C should be a closed polyhedron, and I'd like to convert it to a triangle
> mesh.
>
> To my understanding, I can do the cut with Nef_polyhedron_3::difference().
> So far so good.

I would add that depending on your input shapes, the result might not be
just a closed polyhedron (you might have 1 and 2-dimensional features left
over). These can be discarded by regularization operations.

> Second, I'd like to identify the set of triangles in C which "came from
> B", i.e. the set in intersect(C,B). How would I find these set?

I have successfully done something similar to this for union operations. I
use a custom Mark trait to embed texture information in input facets (this
Mark is a template argument to Nef3). The textures persist through boolean
operations according to mark combination rules that I implement.

This idea can be applied to colour facets according to the shape they
originated from. It should work fine with difference/complement operations
and cascaded operations as well.

This wasn't trivial to achieve out-of-the-box, but it's certainly doable.

Fred

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