CGAL users discussion list

[gang wang <>]

Hi All,
I am confused about Polyhedra edges, and found it difficult to manipulate.

1. I created a project including examples/Polyhedron/polyhedron_prog_cube.cpp, build and run, the result of P.is_tetrahedron(h) is false. Is the fact true?
    Are the figures in the manual(P1488) right?

2. In P1513, said "The opposite() member function returns this halfedge of opposite orientation."
    I edit the below code:
    CGAL_precondition( P.is_valid());
    typedef Polyhedron::Point_3         Point;
    typedef Polyhedron::Halfedge_handle Halfedge_handle;
    Halfedge_handle h = P.make_tetrahedron( Point( 1, 0, 0),
                                            Point( 0, 0, 1),
                                            Point( 0, 0, 0),
                                            Point( 0, 1, 0));
    Halfedge_handle g = h->next()->opposite()->next();             // Fig. (a)
    std::cout << "h" << std::endl;
    std::cout << h->vertex()->point() << std::endl;
    std::cout << h->next()->vertex()->point() << std::endl;
    std::cout << std::endl;

    std::cout << "h opposite" << std::endl;
    Halfedge_handle ho = h->opposite();
    std::cout << ho->vertex()->point() << std::endl;
    std::cout << ho->next()->vertex()->point() << std::endl;
    std::cout << std::endl;
   
    The result is:
    h
    1 0 0
    0 0 1

    h opposite
    0 0 0
    0 1 0
    It seems h opposite is not h of opposite orientation.
    Did I misunderstand something?

3. Is there any other way to construct a polyhedra or 3D surface?

Thanks

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