compile error in CGAL4.6 for a code that successfully compiles in CGAL4.2

Question

I have the following code that is successfully compiled and executed with CGAL4.2.

cgal_intersection.h

typedef struct {double x; double y;} coordinate;

int cgal();

extern "C" int find_intersections_of_curves(
    coordinate *curve_1, long curve_1_size,
    coordinate *curve_2, long curve_2_size,
    coordinate *intersections, int max_num_of_intersections);

cgal_intersection.cpp

#include <CGAL/Cartesian.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arr_polyline_traits_2.h>
#include <CGAL/Sweep_line_2_algorithms.h>
#include <vector>
#include <list>

#include "cgal_intersection.h"

typedef CGAL::Cartesian<double>                    Kernel;
typedef CGAL::Arr_segment_traits_2<Kernel>              Segment_traits;
typedef CGAL::Arr_polyline_traits_2<Segment_traits>     Traits;
typedef Traits::Point_2                                 Point;
typedef Traits::Curve_2                                 Polyline;

extern "C" int find_intersections_of_curves(
    coordinate *curve_1, long curve_1_size,
    coordinate *curve_2, long curve_2_size,
    coordinate *intersections, int max_num_of_intersections)
{

    std::vector<Point> points_1(curve_1_size);
    for (long i_1 = 0; i_1 < curve_1_size; i_1++)
        points_1[i_1] = Point(curve_1[i_1].x, curve_1[i_1].y);
    Polyline  polyline_1(points_1.begin(), points_1.end());

    std::vector<Point> points_2(curve_2_size);
    for (long i_2 = 0; i_2 < curve_2_size; i_2++)
        points_2[i_2] = Point(curve_2[i_2].x, curve_2[i_2].y);
    Polyline  polyline_2(points_2.begin(), points_2.end());

    Polyline polylines[] = {polyline_1, polyline_2};
    std::list<Point> intersection_points;
    CGAL::compute_intersection_points(polylines, polylines + 2,
                                      std::back_inserter(intersection_points));

    int num_of_intersections = intersection_points.size();
    Point intersection_point;
    for (int j = 0; j < num_of_intersections; j++){
        if (j == max_num_of_intersections)
            break;
        intersection_point = intersection_points.front();
        intersections[j].x = intersection_point.x();
        intersections[j].y = intersection_point.y();
        intersection_points.pop_front();
    }

    return num_of_intersections;
}

But when using CGAL4.6, I get a compile error like the following:

Scanning dependencies of target cgal_intersection
[100%] Building CXX object CMakeFiles/cgal_intersection.dir/cgal_intersection.cpp.o
In file included from /home/chan/mose/mose/cgal_intersection/cgal_intersection.cpp:5:0:
/usr/include/CGAL/Sweep_line_2_algorithms.h: In instantiation of ‘OutputIterator CGAL::compute_intersection_points(CurveInputIterator, CurveInputIterator, OutputIterator, bool) [with CurveInputIterator = CGAL::polyline::Polyline_2<CGAL::Arr_segment_2<CGAL::Cartesian<double> >, CGAL::Point_2<CGAL::Cartesian<double> > >*; OutputIterator = std::back_insert_iterator<std::list<CGAL::Point_2<CGAL::Cartesian<double> > > >]’:
/home/chan/mose/mose/cgal_intersection/cgal_intersection.cpp:36:78:   required from here
/usr/include/CGAL/Sweep_line_2_algorithms.h:134:48: error: no type named ‘Traits’ in ‘struct CGAL::Default_arr_traits<CGAL::polyline::Polyline_2<CGAL::Arr_segment_2<CGAL::Cartesian<double> >, CGAL::Point_2<CGAL::Cartesian<double> > > >’
   typename Default_arr_traits<Curve>::Traits   traits;
                                                ^
/usr/include/CGAL/Sweep_line_2_algorithms.h:134:48: error: no type named ‘Traits’ in ‘struct CGAL::Default_arr_traits<CGAL::polyline::Polyline_2<CGAL::Arr_segment_2<CGAL::Cartesian<double> >, CGAL::Point_2<CGAL::Cartesian<double> > > >’
make[2]: *** [CMakeFiles/cgal_intersection.dir/cgal_intersection.cpp.o] Error 1
make[1]: *** [CMakeFiles/cgal_intersection.dir/all] Error 2
make: *** [all] Error 2

I looked into the header files but I don't see why it works in CGAL4.2 but fails in CGAL4.6. I would be grateful for any help.

Answer 1

I successfully compiled the code after two modifications.

1. It turned out that the API of Arr_polyline_traits_2 was changed significantly from CGAL4.2 to CGAL4.4. For example, when using CGAL4.6.1, one should use Construct_curve_2 to construct a polyline, as described in the example code Arrangement_on_surface_2/polylines.cpp.

2. There are two overloaded definitions of compute_intersection_points. Here, one should explicit designate which trait is being used, i.e. one should use the API described at: http://doc.cgal.org/latest/Sweep_line_2/group__PkgIntersectionOfCurves2.html#ga69bf75d5c190cf566c1f6eba93a20a29.

The code that works after incorporating the above modifications are like the following:

// Computing intersection points among curves using the sweep line.
#include <CGAL/Cartesian.h>
#include <CGAL/Arr_segment_traits_2.h>
#include <CGAL/Arr_polyline_traits_2.h>
#include <CGAL/Sweep_line_2_algorithms.h>
#include <vector>
#include <list>

#include "cgal_intersection.h"

typedef CGAL::Cartesian<double>                         Kernel;
typedef CGAL::Arr_segment_traits_2<Kernel>              Segment_traits;
typedef CGAL::Arr_polyline_traits_2<Segment_traits>     Polyline_traits;
typedef Polyline_traits::Point_2                        Point;
typedef Polyline_traits::Curve_2                        Polyline;

extern "C" int find_intersections_of_curves(
    coordinate *curve_1, long curve_1_size,
    coordinate *curve_2, long curve_2_size,
    coordinate *intersections, int max_num_of_intersections)
{
    Polyline_traits polyline_traits;
    Polyline_traits::Construct_curve_2 construct_polyline =
        polyline_traits.construct_curve_2_object();

    int num_of_curves = 2;
    coordinate *curves[] = {curve_1, curve_2};
    long size_of_curve[] = {curve_1_size, curve_2_size};
    std::vector<Polyline> polylines;

    for(int n = 0; n < num_of_curves; n++){
        std::vector<Point> points;
        Point p_0 = Point(curves[n][0].x, curves[n][0].y);
        points.push_back(p_0);
        for(long i = 1; i < size_of_curve[n]; i++){
            Point p_i = Point(curves[n][i].x, curves[n][i].y);
            if(p_i != points.back()){
                points.push_back(p_i);
            }
        }
        polylines.push_back(construct_polyline(points.begin(), points.end()));
    }

    std::list<Point> intersection_points;
    CGAL::compute_intersection_points(polylines.begin(), polylines.end(),
                                      std::back_inserter(intersection_points),
                                      false, polyline_traits);

    int num_of_intersections = intersection_points.size();
    Point intersection_point;
    for (int j = 0; j < num_of_intersections; j++){
        if (j == max_num_of_intersections)
            break;
        intersection_point = intersection_points.front();
        intersections[j].x = intersection_point.x();
        intersections[j].y = intersection_point.y();
        intersection_points.pop_front();
    }

    return num_of_intersections;
}