CGAL users discussion list

[David Coeurjolly <>]

Hi Laurent,

I've almost fixed my problem but without the P.erase_center_vertex()
function: I tried to use it but if you iterate on
P.erase_center_vertex() without controlling the order of the processed
halfedges, it leads to inconsistencies (non manifold surface).

I'll write a more precise reply to the cgal mailing list but here is the
 solution I'm working on:
  - track the intersection edges (edge sharing Interior/exterior
vertices) and create the new halfedges (split_facet)
  - use the erase_facet function to  split the polyhedron into two parts
(while keeping  an handle to the "exterior" part)
  - fill the hole of the "interior" part
  - bruteforce deletion of the exterior part with a
"erase_connected_component" function.

by the way, many thanks Laurent for your answer...

to be continued.

regards,
dav


Laurent Provot wrote:
> Hello David,
> 
> If I have well understood your piece of code you want to remove all the
> incident facets of a vertex (represented by an halfedge v) and if this
> creates an isolated vertex it gets automatically removed as well.
> 
> But isn't it simpler to use the P.erase_center_vertex(...) on your
> exterior vertices ? I guess it gives the same result, doesn't it ?
> 
> Laurent
> 
> 
> Le Wed, 23 May 2007 15:30:24 +0200,
> David Coeurjolly 
> <>
>  a écrit :
> 
>> Dear all,
>>
>> I've to admit that I'm a brand new CGAL user for a couple of weeks and
>> my questions may be stupid. My problem is quite simple: cut a
>> polyhedron with an oriented plane.
>>
>> It is quite easy to tag  the vertices ('exterior/interior') and to
>> create the new halfedges/vertices for intersection points
>> (edge/plane). But I have troubles to "remove" the exterior vertices.
>>
>> More precisely, I've pushed in a list<Halfedge_handle>, an halfedge
>> handle per exterior vertex (called list_exterior_handles) obtained
>> during the exterior vertex scan step. My idea was to use
>> P.erase_facet() as follows:
>>
>> Halfedge_around_vertex_circulator circ;
>> for( list<Halfedge_handle>::iterator v =
>> list_exterior_handles.begin(); v != list_exterior_handles.end() ;
>> ++v){ 
>>      circ = (*v)->vertex_begin();
>>      unsigned int deg = (*v)->vertex()->degree();
>>      for (unsigned int i=0; i< deg; i++)
>>           if (not circ->is_border()) P.erase_facet(circ);
>>      circ++;
>> }    
>>
>> But this does not work..... I obtain segfaults due to the
>> dereferencing of a NULL pointer in the (*v)->vertex()->degree()
>> computation.
>>
>> Do you have any idea of what's going on ? By the way, my choice of the
>> erase_facet operation may not be not good.. Any other suggestion ?
>>
>> Thanks in advance, regards,
>> david
>>
>>
> 

-- 
----------------
David Coeurjolly - Chargé de recherche CNRS
Laboratoire LIRIS-UMR 5205
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