CGAL users discussion list

[Fernando Cacciola <>]

Hi Rob,

> More precisely,  I can't seem to get a good handle on what from the
> EdgeProfile is modified during the collapse. 

The EdgeProfile is local cached "view" of the mesh around the collapsing 
edge.

After the collapse, there is no *explicit* guarantee for the validity of 
the cached elements, just like an iterator over a std::vector might or 
might be valid after removal.

> The EdgeProfile is passed
> to the OnCollapsing function in the visitor *before* the actual collapse
> occurs.  Therefore, some of the information it points to becomes
> invalid, or no longer actually represents the topology of the mesh.

Indeed.

> Can I reverse the edge collapses with just the information from the
> EdgeProfiles passed into OnCollapsing?

Off the top of my head you could also need the "placement" argument 
which indicates where the remaning vertex will be placed. Unless in your 
particular application vertices are not moved.

> Is any of the collapsed info
> discarded (destructed etc.), or should it still reside in memory unused?
The profile stores vertex and halfedge handles, some of which will be 
invalidated after the collapse. Wich ones depends on the actual euler 
operations applied based on the local topology before the collapse 
(topology which is described by the profile)


I'll take a close and I'll get back to you with details on how to 
implement the reverse operation using a stack of edge profiles.


Best

Fernando Cacciola
www.geometryfactory.com