CGAL users discussion list

[Efraim Fogel <>]

You are trying to do something that is currently not supported, but
there is a simple workaround.

The manual of compute_intersection_points() says, and I quote "The
Traits type must be a model of the  ArrangementTraits_2 concept, such
that the value-type of InputIterator is Traits::Curve_2". Gps_traits_2
does not model the  ArrangementTraits_2 concept. As a matter of fact, it
doesn't even define the nested type Curve_2, which is required to be the
value type of the iterators that you pass as input parameters to the
compute_intersection_points() function.

You need to define your input curves as Conic_traits_2::Curve_2. You
will notice that Conic_traits_2::Curve_2 does not have a constructor
that accepts two points. Instead you need to provide the entire set of 6
coefficients that define a general conic, and the endpoints, (which you
have). The first 3 should be zero, and the remaining three are the
coefficients of the underlying line.

Notice that compute_intersection_points() accepts the traits as an
optional parameter. It might be easier to debug if you pass it
explicitly, as in:

  Conic_traits_2 traits;
  compute_intersection_points(iss, iss+1, std::back_inserter (pts),
false, traits);

zickphy wrote:
> Hi, Thanks for your reply.
> The relevant code is all included here. It is simple, but I do not know what
> wrong with this.
>
> -------------------------------------------------------------
> #include <CGAL/basic.h>
> #include <CGAL/Timer.h>
> #include <CGAL/Cartesian.h>
> #include <CGAL/CORE_algebraic_number_traits.h>
> #include <CGAL/offset_polygon_2.h>
> #include <CGAL/Arr_conic_traits_2.h>
> #include <CGAL/Sweep_line_2_algorithms.h>
>
> typedef CGAL::CORE_algebraic_number_traits Nt_traits;
> typedef Nt_traits::Rational Rational;
> typedef Nt_traits::Algebraic Algebraic;
> //struct Rat_kernel : public CGAL::Cartesian<Rational> {};
> //struct Alg_kernel : public CGAL::Cartesian<Algebraic> {};
> //struct Conic_traits_2 : public CGAL::Arr_conic_traits_2<Rat_kernel,
> Alg_kernel, Nt_traits> {};
> typedef CGAL::Cartesian<Rational> Rat_kernel;
> typedef CGAL::Cartesian<Algebraic> Alg_kernel;
> typedef CGAL::Arr_conic_traits_2<Rat_kernel, Alg_kernel, Nt_traits>
> Conic_traits_2;
> typedef Rat_kernel::Point_2 Point_2;
> typedef CGAL::Polygon_2<Rat_kernel> Polygon_2;
> typedef CGAL::Gps_traits_2<Conic_traits_2> Gps_traits_2;
> typedef Gps_traits_2::Polygon_2 Offset_polygon_2;
> typedef Gps_traits_2::Polygon_with_holes_2 Offset_polygon_with_holes_2;
> typedef Gps_traits_2::X_monotone_curve_2 X_monotone_curve_2;
> typedef CGAL::Arrangement_2<Gps_traits_2> Arrangement_2;
> typedef Gps_traits_2::Point_2 Query_Point_2;
>
> using namespace std;
>
> void main()
> { 
>       Query_Point_2 pt1(0, 0); 
>       Query_Point_2 pt2(0, 10); 
>       Query_Point_2 pt3(10, 0); 
>       Query_Point_2 pt4(0, 10); 
>       std::list<Query_Point_2> pts; 
>       X_monotone_curve_2 is1(pt1, pt2); 
>       X_monotone_curve_2 is2(pt3, pt4); 
>       X_monotone_curve_2 iss[] = {is1, is2}; 
>
>       compute_intersection_points(iss, iss+1, std::back_inserter (pts)); 
> }
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