CGAL users discussion list

[Guillaume Damiand <>]

Le 03/12/2014 15:31, Per Zetterlund a écrit :
> To split the non-manifold vertices to get
> a manifold, closed mesh is pretty easy.
> But to split the non-manifold edges and
> still have a closed mesh is hairier. But
> perhaps I just haven't figured it out yet.
>
>   /Per

Hi Per,

Another possibility, convert the Triangulation_3 into a 3D linear cell 
complex (see CGAL::import_from_triangulation_3 [1]), then remove all the 
faces (using remove_cell<2>(lcc, d) [2]) of the LCC that do not belong 
to the boundary (to test if a dart d of a face belongs to the boundary, 
just use lcc.is_free<3>(d) [3]).

Guillaume


[1] 
http://doc.cgal.org/latest/Linear_cell_complex/group__PkgLinearCellComplexConstructions.html#ga7e8cde514b93c3441a4df2bc09c24068
[2] 
http://doc.cgal.org/latest/Combinatorial_map/group__PkgCombinatorialMapsOperations.html#gab70174b3358188a92dd3a0a054d02e42
[3] 
http://doc.cgal.org/latest/Combinatorial_map/classCombinatorialMap.html#acde359e3f68495a16b1eb615c23b6615



> On Wed, Dec 3, 2014 at 2:38 PM, Sebastien Loriot (GeometryFactory)
> <>
>  wrote:
> > On 12/03/2014 02:23 PM, Per Zetterlund wrote:
> > > As far as I understand, it can extract
> > > a manifold Polyhedron as long as the the
> > > surface embedded in the triangulation
> > > actually is manifold. It does not in any
> > > way enforce or aid in the process of making
> > > the surface manifold, right?
> > Right.
> >
> > > When I try it I get lots of errors such as
> > >
> > > CGAL::Polyhedron_incremental_builder_3<HDS>::
> > > add_vertex_to_facet(): input error: disconnected facet complexes at vertex
> > > 352:
> > >              involved facets are: 1815 1814 1813 (closed cycle) and.
> > > terminate called after throwing an instance of 'CGAL::Assertion_exception'
> > >     what():  CGAL ERROR: assertion violation!
> > > Expr: check_protocoll == 1
> > > File: /usr/local/include/CGAL/Polyhedron_incremental_builder_3.h
> > > Line: 225
> > > Aborted (core dumped)
> > >
> > > I guess that is because the embedded surface
> > > was not manifold.
> > Most probably.
> > A simple hack is to duplicate the non-manifold vertices.
> >
> > Sebastien.
> >
> >
> > >    /Per
> > >
> > >
> > >
> > >
> > > On Tue, Dec 2, 2014 at 1:32 PM, Sebastien Loriot (GeometryFactory)
> > > <>
> > >  wrote:
> > > > On 11/24/2014 09:10 AM, Per Zetterlund wrote:
> > > > > Hi all,
> > > > >
> > > > > This is an issue I've run into several times
> > > > > in different applications. Say that I have a
> > > > > Triangulation_3 and I do a binary labelling of
> > > > > the cells. Then I want to extract the interface
> > > > > surface between the labels as a manifold
> > > > > Polyhedron_3. Often it happens that that the
> > > > > topology of the actual triangle faces in the
> > > > > triangulation is not manifold. Are there any
> > > > > routines in CGAL to extract a manifold surface
> > > > > from a triangulation that (in some sense) is
> > > > > close to the true interface surface?
> > > >
> > > >
> > > > There is nothing working out-of-the-box but looking
> > > > at the file CGAL/IO/Complex_2_in_triangulation_3_polyhedron_builder.h
> > > > should give you ideas of how a manifold surface mesh is extracted
> > > > from a 3D triangulation.
> > > >
> > > > Sebastien.
> > > >
> > > > > Any ideas?
> > > > >
> > > > >     /Per
> > > >
> > > > --
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Guillaume DAMIAND

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