CGAL users discussion list

[Josh Stratton <>]

The first is a patch of four quads (say facet A, B, C, and D labeled
from top-left, top-right, bottom-left, bottom-right).  This is a
2-manifold surface that can be represented in a polyehdron_3, correct?
 So if face B is removed, it is still a 2-manifold polyedron.  What
would happen in CGAL if facet C is then removed?  Would that result in
a run-time error?

On Sat, Oct 1, 2011 at 9:35 AM, Guillaume Damiand
<>
 wrote:
> 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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