CGAL users discussion list

["Sebastien Loriot (GeometryFactory)" <>]

Hello,

From what I understand you probably need to use the 
Polyhedron_incremental_builder_3.

Have a look here for the documentation (there is an example at the end 
of the page)
http://www.cgal.org/Manual/last/doc_html/cgal_manual/Polyhedron_ref/Class_Polyhedron_incremental_builder_3.html

S.



 wrote:
> Dear programmers,
>
> I've drawn this question but no one has given me an answer. I would really
> appreciate it so much if someone could even give me a hint to solve this
> problem. It's really very important for me.
>
> Thank you in advance,
>
> Sincerely,
> Samer
>
> ---------------------------- Original Message ----------------------------
> Subject: [cgal-discuss] Tetrahedron-Polyhedron problem
> From:    "Samer Afach" 
> <>
> Date:    Fri, March 12, 2010 5:15 pm
> To:      
>
> --------------------------------------------------------------------------
>
> Hello :),
>
> I'm starting to create some simple polyhedra in order to go to bigger
> applications, and so I'm trying to understand how this library works
> with it.
>
> I have a problem, the problem is that I'm failing to create 4 triangles
> and form a tetrahedron from them. I'm avoiding using the function
> Polyhedron::make_tetrahedron(...) because my aim in the future is
> creating random polyhedra by combining triangles and check whether they
> are closed and fulfill some conditions. Here's my program:
>
> #include <CGAL/Homogeneous.h>
> #include <CGAL/Polyhedron_traits_with_normals_3.h>
> #include <CGAL/Polyhedron_3.h>
> #include <iostream>
> #include <algorithm>
>
> using namespace std;
>
> struct Normal_vector
> {
>     template <class Facet>
>     typename Facet::Plane_3 operator()( Facet& f) {
>     typename Facet::Halfedge_handle h = f.halfedge();
>     // Facet::Plane_3 is the normal vector type. We assume the
>     // CGAL Kernel here and use its global functions.
>     return CGAL::cross_product(
>     h->next()->vertex()->point() - h->vertex()->point(),
>     h->next()->next()->vertex()->point() - h->next()->vertex()->point());
>     }
> };
>     typedef CGAL::Homogeneous<int> Kernel;
>     typedef Kernel::Point_3 Point_3;
>     typedef Kernel::Vector_3 Vector_3;
>     typedef CGAL::Polyhedron_traits_with_normals_3<Kernel> Traits;
>     typedef CGAL::Polyhedron_3<Traits> Polyhedron;
>     typedef Polyhedron::Halfedge_handle Halfedge_handle;
>     int main() {
>     Point_3 p( 1, 0, 0);
>     Point_3 q( 0, 1, 0);
>     Point_3 r( 0, 0, 1);
>     Point_3 s( 0, 0, 0);
>     Polyhedron P;
>     //P.make_tetrahedron( p, q, r, s);
>
>     P.make_triangle(p,q,r);
>     P.make_triangle(p,r,s);
>     P.make_triangle(p,s,q);
>     P.make_triangle(q,s,r);
>
>     if(P.is_closed())
>     {
>         cout<<"It's closed"<<endl;
>     }
>     if(P.is_pure_trivalent())
>     {
>         cout<<"Trivalent"<<endl;
>     }
>     std::transform( P.facets_begin(), P.facets_end(), P.planes_begin(),
>     Normal_vector());
>     CGAL::set_pretty_mode( std::cout);
>     std::copy( P.planes_begin(), P.planes_end(),
>     std::ostream_iterator<Vector_3>( std::cout, "\n"));
>     return 0;
> }
>
> I copied this program from a sample in the manual. What's confusing me
> is that when I create a tetrahedron using the make_tetrahedron function,
> the conditions work fine, but I can't get the same output when creating
> a tetrahedron by "connecting" 3 dimensional triangles. I was even
> careful having the same output as the example (same order for the norms)
>
> Could anyone please tell me why that's happening, and I would appreciate
> it so much if someone also could apply the function
> Polyhedron::is_tetrahedron(Polyhedron::Halfedge_handle) also, because I
> failed to do it because I didn't know how to get the right call for
> Halfedge_handle.
>
> Sincerest regards,
> Samer Afach
> Institute of computational physics, University of Stuttgart