CGAL users discussion list

["Wesley Smith" <>]

I'm working on getting 3D voronoi information from
Delaunay_triangulation_3 and am getting some information I'm not sure
is valid.  The points in the triangulation are:

(0, 0, 0)
(1, 0, 0)
(0, 1, 0)
(0, 0, 1)
(1, 1, 1)

These are the cells
p0: 0 0 0
p1: 1 0 0
p2: 0 1 0
p3: 0 0 1
dual: 0.5 0.5 0.5

p0: 1 0 0
p1: 1 1 1
p2: 0 1 0
p3: 0 0 1
dual: 0.5 0.5 0.5


And the duals for the finite facets:

segment:
p0: 0.5 0.5 0.5
p1: 0.5 0.5 0.5

What I'm trying to figure out is why I get a degenerate segment
(basically a point) as the only dual.  The code for getting the duals
looks like:



        for(Finite_facets_iterator fi = T.finite_facets_begin();
                fi != T.finite_facets_end();
                fi++)
        {
                CGAL::Object o = T.dual(*fi);
                
                if(const Segment * seg = CGAL::object_cast<Segment>(&o)) {
                        
                        Point p0 = seg->vertex(0);
                        Point p1 = seg->vertex(1);
                }
        }


Is this how it's supposed to be done?  I'm trying to figure out how
Object works but am not sure if I got it right.  The entire code is
here:

#include <CGAL/basic.h>

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>

#include <CGAL/Delaunay_triangulation_3.h>
#include <CGAL/Triangulation_cell_base_with_circumcenter_3.h>

#include <CGAL/IO/Triangulation_geomview_ostream_3.h>

#include <iostream>

// exact constructions (circumcenter computations) are needed in this
// demo, not only predicates
typedef CGAL::Exact_predicates_exact_constructions_kernel K;

typedef CGAL::Triangulation_vertex_base_3<K>                 Vb;
typedef CGAL::Triangulation_cell_base_with_circumcenter_3<K> Cb;
typedef CGAL::Triangulation_data_structure_3<Vb, Cb>         TDS;
typedef CGAL::Delaunay_triangulation_3<K, TDS>               Triangulation;
// typedef CGAL::Delaunay_triangulation_3<K> Triangulation;

typedef Triangulation::Cell_handle                                      
Cell_handle;
typedef Triangulation::Finite_cells_iterator            Finite_cells_iterator;

typedef Triangulation::Point          Point;
typedef Triangulation::Finite_facets_iterator           
Finite_facets_iterator;
typedef Triangulation::Segment                                          
Segment;

int main()
{
        Triangulation T;

        std::cout <<"          Inserting points" << std::endl ;
        
        T.insert(Point(0, 0, 0));
        T.insert(Point(1, 0, 0));
        T.insert(Point(0, 1, 0));
        T.insert(Point(0, 0, 1));
        T.insert(Point(1, 1, 1));
        
        for(Finite_cells_iterator it = T.finite_cells_begin(); it !=
T.finite_cells_end(); it++) {
                Cell_handle c = it;
                Point p0 = c->vertex(0)->point();
                Point p1 = c->vertex(1)->point();
                Point p2 = c->vertex(2)->point();
                Point p3 = c->vertex(3)->point();
                
                Point dual = T.dual(c);
                
                std::cout << std::endl;
                std::cout << "p0: " << p0.x() << " " << p0.y() << " " << 
p0.z() << std::endl;
                std::cout << "p1: " << p1.x() << " " << p1.y() << " " << 
p1.z() << std::endl;
                std::cout << "p2: " << p2.x() << " " << p2.y() << " " << 
p2.z() << std::endl;
                std::cout << "p3: " << p3.x() << " " << p3.y() << " " << 
p3.z() << std::endl;
                
                std::cout << "dual: " << dual.x() << " " << dual.y() << " " <<
dual.z() << std::endl;
        }
        
        int segments = 0;
        for(Finite_facets_iterator fi = T.finite_facets_begin();
                fi != T.finite_facets_end();
                fi++)
        {
                CGAL::Object o = T.dual(*fi);
                
                if(const Segment * seg = CGAL::object_cast<Segment>(&o)) {
                        printf("\nsegment: %d\n", segments);
                        segments++;
                        
                        Point p0 = seg->vertex(0);
                        Point p1 = seg->vertex(1);
                        
                        std::cout << "p0: " << p0.x() << " " << p0.y() << " " 
<< p0.z() << std::endl;
                        std::cout << "p1: " << p1.x() << " " << p1.y() << " " 
<< p1.z() << std::endl;
                }
        }

        return 0;
}