CGAL users discussion list

[Louis <>]

Thanks for the information Pedro. Initially I didn't set the
neighborhood information because I don't know what are done
automatically in by the data structure itself or what the user has to
specify. When I insert a vertex or face, calling vertex.is_valid() or
face.is_valid() all returned true. But the triangulation data
structure remained invalid. Now after I set the neighborhood
information, the triangulation still says it's invalid. I'm also not
sure about boundary faces where 1 or 2 neighbor faces are not defined,
do I need to do anything special in this case?

What's frustrating is the lack of information in the documentation on
what are the necessary steps to build a valid triangulation using this
data structure. There are many weird behaviors in this data structure
that need answers. Why does the class initialize with 0 vertices, 1
face, 1 edge? Calling tds.clear() made sure they became 0, but when
you add the first vertex, somehow it's not counted
(number_of_vertices() returns 0).

I wonder if anyone has a concrete example or maybe skeleton code that
shows how to build a triangulation data structure from vertices and
faces.

Thanks,
Louis


On Tue, Mar 25, 2008 at 7:27 AM, Pedro Machado Manhães de Castro
<>
 wrote:
> I meant stuffs like:
>
> fHandle->set_neighbor(0, some_face_handle_1);
> fHandle->set_neighbor(1, some_face_handle_2);
> fHandle->set_neighbor(2, some_face_handle_3);
> sry (to not confuse even more),
> Pedro
>
>
>
> On Tue, Mar 25, 2008 at 3:25 PM, Pedro Machado Manhães de Castro
> <>
>  wrote:
> > Hello,
> >
> > Do you define the neighborhood of your face inside your 2nd for iteration?
> >
> > Stuffs like:
> > fHandle->set_neighbor(0, some_face_handle_1);
> > fHandle->set_neighbor(0, some_face_handle_2);
> > fHandle->set_neighbor(0, some_face_handle_3);
> > inside
> >
> > ?
> >
> > This constructor here is easier to use:
> > create_face(Face_handle f1, int i1,
> >                    Face_handle f2, int i2,
> >                    Face_handle f3, int i3)
> >
> > You define a face by its 3 neighbors, i1, i2, i3 are any sequence defined
> by the indices 0, 1, 2.
> >
> > Hope it could help,
> > Best Regard,
> > Pedro Machado
> >
> >
> >
> >
> >
> > On Tue, Mar 25, 2008 at 11:43 AM, Louis Feng 
> > <>
> wrote:
> >
> > > Hello,
> > >
> > > I'm trying to construct a 2D triangle mesh from a list of vertices and
> > > faces. I didn't want to use Polyhedron because I needed some properties
> from
> > > the 2D triangulation class. I'm using Triangulation_2 and
> > > Triangulation_data_structure_2. Basically I use T.tds() to get a
> reference
> > > to the internal data structure. Then I add vertices and faces to it. But
> > > this has become very confusing and I couldn't find examples on this.
> > >
> > > An outline of my code:
> > >
> > > triDS.set_dimension(2);
> > > for(...) {
> > >  VertexHandle vHandle = triDS.create_vertex();
> > >  vHandle->set_point(Point2(...));
> > > }
> > > for(...) {
> > >  FaceHandle fHandle = triDS.create_face(vHandle1, vHandle2, vHandle3); }
> > >
> > > When I check triDS.is_valid() at the end, it returns false. More
> > > interestingly, before I add anything to triDS, when I check the
> vertices,
> > > edge, etc. I get this
> > >
> > > Triangulation vertices: 0
> > > Triangulation faces: 1
> > > Triangulation full faces: 1
> > > Triangulation edges: 1
> > >
> > > So am I suppose to clear this before I add something to it? Looking at
> the
> > > template file for the data structure, it check this:
> > >
> > > case 2:
> > >    result = result &&  edge_count == 3*face_count/2 ;
> > >    CGAL_triangulation_assertion(edge_count == 3*face_count/2);
> > >    break;
> > >
> > > I'm not sure what the expected behavior is. Could someone tell me what
> I'm
> > > doing wrong and how this class suppose to be used? Thanks!
> > >
> > > Louis
> > >
> > > --
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> > >
> >
> >
>
>