CGAL users discussion list

[Camille Wormser <>]

> > CGAL error: precondition violation!
> > Expr: circulator_size(h->vertex_begin()) >= size_type(3)
> > while trying to remove a halfedge
>
> This means that you have degenerate faces, probably because some of  
> the collapsing you did before was not acceptable, because the link  
> condition was not satisfied.


Sorry, I answered a bit too fast:

In fact it means that there is a vertex with only 2 incident edges.  
This can happen when you join facets (my link condition was not  
relevant, since you do not maintain a triangulation), and it is  
perfectly valid.

The problem is that you cannot join two facets whose common boundary  
consists in two or more consecutive edges: it would result in a  
dangling edge.

To deal with that, you should first remove this degree 2 vertex by  
joining it with one of its two neighbors, check that these two  
neighbors have degree greater than 2 (otherwise apply the same  
treatment), and then you can merge the two facets.
--
Camille