Customizing CGAL Kernel with my own Point class

Question

I would like to use a custom Point class with the CGAL constrained delaunay triangulation. However, with the following MyPoint class (which should behave the exact same as a CGAL::Point_2 no?) I get segmentation faults. It works perfectly if I set the Point_2 typedef inside MyKernel to CGAL::Exact_predicates_inexact_constructions_kernel::Point_2. What am I doing wrong?

template<class P>
struct MyPoint : public P {
    MyPoint() : P() {}
    MyPoint(const MyPoint& p) : P(p) {}

    MyPoint( int x, int y) : P(x,y) {}
    MyPoint( double x, double y) : P(x,y) {}
};

struct MyKernel : CGAL::Exact_predicates_inexact_constructions_kernel {
    typedef MyPoint<CGAL::Exact_predicates_inexact_constructions_kernel::Point_2> Point_2;
};

typedef MyKernel K;

typedef CGAL::Triangulation_vertex_base_2<K>                     Vb;
typedef CGAL::Constrained_triangulation_face_base_2<K>           Fb;
typedef CGAL::Triangulation_data_structure_2<Vb,Fb>              TDS;
typedef CGAL::Exact_predicates_tag                               Itag;
typedef CGAL::Constrained_Delaunay_triangulation_2<K, TDS, Itag> CDT;
typedef CDT::Point          Point;

Code which segfaults at last line:

CDT cdt;
Point cgal_p1;
Point cgal_p2;
cgal_p1 = Point(p1[1],p1[2]);
cgal_p2 = Point(p2[1],p2[2]);
cdt.insert_constraint(cgal_p1,
                      cgal_p2);

Answer 1

Changing the kernel is tricky. What happens here is that, seen from the triangulation class, the only thing that changes compared to the kernel is the point type, by deriving from it. This can be good enough for predicates functors, but not for constructions functors, like the intersection that is required by the CDT.

I think you have two options :

1. Write the full traits interface for ConstrainedTriangulationTraits_2 for your types.

2. Use the Extensible Kernel mechanism that is supposed to do what you want.