CGAL users discussion list

[Guillaume Damiand <>]

Le 01/10/2011 00:05, Josh Stratton a écrit :
> I had a quick question regarding the half-edge data structure present
> in CGAL.  I've read over the documentation several times and
> understand that the mesh must be 2-manifold and doesn't support holes
> inside facets, which is fine.  What I couldn't find however, was
> whether the structure supports singular vertices, where one vertex is
> attached to multiple non-joining facets.
>
> *---*---*
> |     |    |
> *---*---*
> |     |    |
> *---*---*
>
>
>
> *---*
> |     |
> *---*---*
>        |    |
>        *---*
>
> For the vertex in the middle bridging the two facets, it will only
> point to an edge on one of the two faces.  Looking over the API, I
> don't see anything that allows lookup of the other face given just the
> vertex.  Is this not a supported mesh configuration in CGAL's
> half-edge implementation, or is it okay, but requires additional code
> to handle these cases?

I don't understand your first example.

The second one is not a 2-manifold, thus it can not be represented by a 
Polyhedron_3 (by definition).

You can  add the surrounding face englobing your two squares => you 
obtain a 2 manifold and thus one vertex (this is probably always the 
case for Polyhedron_3 but I am not sure...)



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