CGAL users discussion list

["Shi Yan" <>]

hello folks, Lutz and Fernando,

i need the edge collapsing feature in my program which is not
supported by the CGAL polyhedron_3 class. so i checked out the one
implemented by Fernando as part of the mesh simplification program.

that edge collapsing routine uses join_vertex() for collapsing. but it
seems that this routine doesn't check the 2-edge loop situation before
joining the vertices.

suppose we have two vertices, one is P and the other is T, and now on
the polyhedron, we have two edges PT and TP, that form a two edge
loop.

what will happen, if i want to collapsing PT, or join the vertex T
pointed by the half-edge PT?


i've made up such a model for testing, it seemed that the join_vertex
call can pass, but the result model cannot pass the
polyhedron.is_valid() check.



i don't think this is right, at lease, "no two edge loop" should be a
precondition of the join_vertex() routine, because collapsing a
halfedge on a two edge loop caused my program to crash.

a half-edge Euler Operator should return a valid half-edge structure
when finished, but it seems not the case here.


thank you.