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["Sebastien Loriot (GeometryFactory)" <>]

魏华祎 wrote:
> Thanks, Sebastien,
>
>       After some tests, I found that when I create a new "Triangulation 
> tri;", there already exist a face in tri, too. So I 
> use  "tri.tds().faces().clear(); " to clear it before I create my own 
> triangulation. Then the numbers of vertices and faces in tri are rihgt now.
>
>     But I don't understand, for a empty triangulation, why it include a 
> face in it?
It is an implementation details.

To make things clean, you should use these functions for the 3 first points:

Vertex_handle t.insert_first ( Point p)
Vertex_handle t.insert_second ( Point p)
Vertex_handle t.insert_in_face ( Point p, Face_handle f)

S.

> Huayi
>
>  
>
> On Sun, May 22, 2011 at 11:43 PM, Sebastien Loriot (GeometryFactory) 
> <sloriot.ml <http://sloriot.ml>@gmail.com <http://gmail.com>> wrote:
>
>     If you want to create your own triangulation, all operations
>     must be done at the TDS level. The TDS knows nothing about
>     finite or infinite simplices, they are simply simplices.
>
>     So the answer is yes, you need to create them.
>
>     S.
>
>     魏华祎 wrote:
>
>         Hi, Sebastien,
>
>            Thanks for your reply. Yes, you are right, the infinite
>         vertex is already present there. But, what about the infinite
>         faces? Do I need create them explicitly? The output of
>         tri.number_of_faces() is still three. It should be two.
>            
>         Huayi
>
>         On Sun, May 22, 2011 at 11:29 PM, Sebastien Loriot
>         (GeometryFactory) <sloriot.ml <http://sloriot.ml>
>         <http://sloriot.ml>@gmail.com <http://gmail.com>
>         <http://gmail.com>> wrote:
>
>            The infinite vertex is already present in the triangulation even
>            when empty, so you don't need to create it.
>
>            S.
>
>
>
>            魏华祎 wrote:
>
>
>                 Hi, everyone,
>                          I have a 2d simple triangulation with four
>         vertices:
>                p1 = (0,0),  p2 = (1,0), p3  = (1,1), p4 = ( 0,1),  and two
>                triangles: (p2, p3, p1) and (p4,p1,p3). And I want to
>         construct
>                a object of Triangulation_2 class, explicitly ( not write
>         these
>                information into files, then use >> read them). The
>         following is
>                my code. But at last, I got five finite vertices and three
>                finite faces. I am confused,  can anyone give me some
>                suggestions about it?  Thanks very much!
>
>                   By the way, I follow the code of  the "file_input" member
>                function in Triangulation_data_structure_2.h to write my
>         own code.
>
>
>
>                #include
>         <CGAL/Exact_predicates_inexact_constructions_kernel.h>
>                #include <CGAL/IO/Color.h>
>                #include <CGAL/Triangulation_2.h>
>
>                #include <CGAL/Triangulation_face_base_2.h>
>                #include <CGAL/Triangulation_vertex_base_2.h>
>
>                typedef
>         CGAL::Exact_predicates_inexact_constructions_kernel K;
>                typedef CGAL::Triangulation_vertex_base_2<K> Vb;
>                typedef CGAL::Triangulation_face_base_2<K> Fb;
>                typedef CGAL::Triangulation_data_structure_2<Vb,Fb> Tds;
>                typedef CGAL::Triangulation_2<K,Tds> Triangulation;
>
>                typedef Triangulation::Face_handle Face_handle;
>                typedef Triangulation::Vertex_handle Vertex_handle;
>                typedef Triangulation::Point Point;
>
>                typedef Triangulation::Finite_vertices_iterator Fvi;
>
>                int main(){
>
>
>                 int n = 4, m = 2, d = 2;
>                 std::vector<Point> P(4);
>                 P[0] = Point(0,0);
>                 P[1] = Point(1,0);
>                 P[2] = Point(1,1);
>                 P[3] = Point(0,1);
>
>                 std::vector<Vertex_handle> V(n+1);
>                 std::vector<Face_handle> F(m);
>
>                 Triangulation tri;
>                 tri.tds().set_dimension(d);
>                 // if I comment the following two lines, there will four
>         finite
>                vertices, but still three faces
>                 V[0] = tri.tds().create_vertex();        
>          tri.set_infinite_vertex(V[0]); // set the infinite vertex of tri
>
>                 // create the vertex_handles
>                 for(int i = 1; i< 5;i++){
>                   V[i] = tri.tds().create_vertex();
>                   V[i]->set_point(P[i-1]);
>                 }
>
>                 //create the first face and set its vertices
>                 F[0] = tri.create_face();
>                 F[0]->set_vertex(0,V[2]);
>                 V[2]->set_face(F[0]);
>
>                 F[0]->set_vertex(1,V[3]);
>                 V[3]->set_face(F[0]);
>
>                 F[0]->set_vertex(2,V[1]);
>                 V[1]->set_face(F[0]);
>
>                 // create the second face and set its vertices
>                 F[1] = tri.create_face();
>                 F[1]->set_vertex(0,V[4]);
>                 V[4]->set_face(F[1]);
>
>                 F[1]->set_vertex(1,V[1]);
>                 V[1]->set_face(F[1]);
>                   F[1]->set_vertex(2,V[3]);
>                 V[3]->set_face(F[1]);
>
>                 // set neighbor information
>                 F[0]->set_neighbor(0,F[1]);
>                 F[1]->set_neighbor(0,F[0]);
>
>                
>         std::cout<<tri.number_of_vertices()<<std::endl<<tri.number_of_faces()<<std::endl;
>
>                 return 0;
>                }
>
>
>
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