CGAL users discussion list

[Monique Teillaud <>]

Dennis Endt wrote:
> Hi Monique,
>
> yes I have had a look.
>
> But it seemed to work with the 3d Delaunay Triangulation and so it
> didn`t matter.

It worked of course, since cgal 3d triangulations are working.
But apparently it did not give you what you wanted.

> But now I found this situation.

but have you read the 2d triangulation manual...?

> So plz tell me if I`m wrong:
>
> Because I don`t know which wall is a vertical or a horizontal wall and
> so on I would use:
>
> CGAL::Triangulation_euclidean_traits_xy_3<K>
> CGAL::Triangulation_euclidean_traits_xz_3<K>
> and CGAL::Triangulation_euclidean_traits_yz_3<K>
>
> for every of my fassades and then merge the results of all of them?
>
> Could this work? Or is there a more simple way to do this?

no
If you are lucky (= your points really don't belong to a plane parallel 
to any xy,xz,yz plane), you will get the same triangulation three times, 
which is not what you want (I guess so). Yhen using one of these random 
traits should give you what you want.
If you are less lucky, one of the computationa will crash. Then, use one 
of the other two.
I'm afraid that's the best you can do if you don't know anything about 
your data, except the fact that they are almost coplanar.

> Two other questions:
> How do I get the points of an edge of a 2d Delaunay Triangulation:
>
> for(Delaunay::Finite_edges_iterator ie = T.finite_edges_begin(); ie !=
> T.finite_edges_end(); ie++)
> {
>     ie->first->vertex(ie->second)->point() // doesn`t work so far
>     ie->first->vertex(ie->third)->point()
> }

You can not just use your 3d code and hope it will work in 2d now. 
Please have a look at the 2d triangulation manual and read how edges are 
represented. Also, there have been several recent threads answering 
similar questions recently.

> What`s wrong on this:
> for(Delaunay::Finite_faces_iterator it = T.finite_faces_begin(); it !=
> T.finite_faces_end(); it++)
> {
>                 Triangle_3 delaunayTriangle = T.triangle(*it);  // error
> }

the 2d triangulation does not have a Triangle_3

again, please read the 2d triangulation manual, this will solve most of 
your questions.

best,
        Monique Teillaud