CGAL users discussion list

[Monique Teillaud <>]

Dennis Endt wrote:
> Hi,
>
> this a quite ok Triangulation:

this looks like a 2d triagulation, it looks ok, but 2d.

> In the other case I have overlapping edges and triangles. 

Your input points don't look coplanar, do they? you just get 3d 
tetraedra, which is what you must get when you compute a 3d triangulation.
3d is ok, for a Delaunay_triangulation_3.

> That`s a big problem.
>
> This is the other fassade on the back side of the building.
>
> Why is the result so different  and how can I avoid this behaviour?

If you want a 2d triangulation, then take coplanar points a input, and 
compute a Delaunay_triangulation_2 in that plane.

> Manuel Caroli schrieb:
> > Hi Dennis,
> >
> > I don't actually understand what is wrong about that. The 
> > triangulation in your picture looks quite ok to me.
> > Also e.g. in your finite_edge_iterator loop you only get finite edges, 
> > so if your triangulation contains only 4 points it is a tetrahedron 
> > which consists of 6 edges.
> >
> > best
> >
> > Manuel
> >
> >
> >
> > Dennis Endt wrote:
> > > Here is a Screenshot of that waht CGAL returns.
> > >
> > > And here are the points to that fassade:
> > > 2585709.716 5703009.266 3.0
> > > 2585710.5465 5703008.192 8.0
> > > 2585711.377 5703007.118 3.0
> > > 2585711.377 5703007.118 0.0
> > > 2585709.716 5703009.266 0.0
> > >
> > > That not the only case where CGAL returns a wrong number of edges or 
> > > facets.
> > >
> > > What have I to do to get a clean triangulation?
> > >
> > > Best,
> > > Dennis
> > >
> > > Dennis Endt schrieb:
> > > > Hi,
> > > >
> > > > I`ve a problem with the 3D Delaunay Triangulation. I want to 
> > > > triangulate
> > > > buildings with multiple fassades. Ech fassade contains of a certain
> > > > number of vertices.
> > > >
> > > > That`s my code:
> > > > #include <CGAL/Simple_cartesian.h>
> > > > #include <CGAL/Filtered_kernel.h>
> > > > #include <CGAL/Delaunay_triangulation_3.h>
> > > >
> > > > typedef CGAL::Simple_cartesian<double> SK;
> > > > typedef CGAL::Filtered_kernel<SK> FK;
> > > > struct K : public FK {};
> > > > typedef K::Point_3 Point_3;
> > > > typedef K::Triangle_3 Triangle_3;
> > > > typedef CGAL::Delaunay_triangulation_3<K> Triangulation;
> > > >
> > > > .
> > > > .
> > > > .
> > > >
> > > > Triangulation T..... // the Triangulation object of my current fassade
> > > >
> > > > for(Triangulation::Finite_edges_iterator ie = 
> > > > T.finite_edges_begin(); ie
> > > > != T.finite_edges_end(); ie++)
> > > > {
> > > >     // The problem is, that the number of infinite_edges is too high.
> > > > For example the number of vertices is 5, he gives me 9 edges or 4 
> > > > and he
> > > > gives me 6 edges.
> > > > }
> > > >
> > > > Why does he gives me so a large number of edges? I would expect 7 or 5
> > > > so far. What can I do, about to get a clean and good triangulation of
> > > > each of my fassades?
> > > >
> > > > Best,
> > > > Dennis
> > > >   
> > >
> > >
> > > ------------------------------------------------------------------------