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[Nicklas SB Karlsson <>]

In attached files I do this for polygon. Have complete program that compile and run if you need?

Did not find any examples so had to struggle a while before I figured how it should be done so guess maybe this help you how to solve your problem.

Nicklas Karlsson

sön 2025-06-22 klockan 17:45 +0800 skrev ж��:

I submitted three straight lines and one circular arc to the CGAL Arrangement, as shown in the left figure. The final calculation result, shown in the right figure, is incorrect. However, if I discretize the arc into line segments, the result becomes correct. so how to do .

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卸甲

 

#ifndef CONSTRUCT_POLYGON_CPP_INCLUDED
#define CONSTRUCT_POLYGON_CPP_INCLUDED

#include "construct_polygon.hxx"

void add_to_polygon (Polygon_2& pgn, const K_Point_2& source,
                     const K_Point_2& mid, const K_Point_2& target)
{
    std::list<CGAL::Object> objects;

    {
        Traits_2 traits;
        Curve_2 circular_arc(source, mid, target);

        traits.make_x_monotone_2_object() (circular_arc, std::back_inserter(objects));
    }
    //assert(objects.size() == 2);

    // Construct the polygon.
    for (std::list<CGAL::Object>::iterator iter = objects.begin(); iter != objects.end(); ++iter)
    {
        X_monotone_curve_2 arc;

        CGAL::assign (arc, *iter);
        pgn.push_back(arc);
    }
}

void add_to_polygon (Polygon_2& pgn, Curve_2& circular_arc)
{
    std::list<CGAL::Object> objects;

    {
        Traits_2 traits;

        traits.make_x_monotone_2_object() (circular_arc, std::back_inserter(objects));
    }
    //assert(objects.size() == 2);

    // Construct the polygon.
    for (std::list<CGAL::Object>::iterator iter = objects.begin(); iter != objects.end(); ++iter)
    {
        X_monotone_curve_2 arc;

        CGAL::assign (arc, *iter);
        pgn.push_back(arc);
    }
}

Polygon_2 construct_polygon (const K_Circle_2& circle)
{
    // Subdivide the circle into two x-monotone arcs.
    Traits_2 traits;
    Curve_2 curve (circle);
    std::list<CGAL::Object>  objects;
    traits.make_x_monotone_2_object() (curve, std::back_inserter(objects));
    assert(objects.size() == 2);

    // Construct the polygon.
    Polygon_2 pgn;
    X_monotone_curve_2 arc;
    std::list<CGAL::Object>::iterator iter;
    for (iter = objects.begin(); iter != objects.end(); ++iter)
    {
        CGAL::assign (arc, *iter);
        auto p0 = arc.source();
        auto p1 = arc.target();

        pgn.push_back (arc);
    }
    return pgn;
}

// Construct a polygon from a rectangle.
Polygon_2 construct_polygon (const K_Point_2& p1, const K_Point_2& p2,
                             const K_Point_2& p3, const K_Point_2& p4)
{
    Polygon_2 pgn;
    X_monotone_curve_2 s1(p1, p2);
    pgn.push_back(s1);
    X_monotone_curve_2 s2(p2, p3);
    pgn.push_back(s2);
    X_monotone_curve_2 s3(p3, p4);
    pgn.push_back(s3);
    X_monotone_curve_2 s4(p4, p1);
    pgn.push_back(s4);
    return pgn;
}

#endif // CONSTRUCT_POLYGON_CPP_INCLUDED

#ifndef CONSTRUCT_POLYGON_HXX_INCLUDED
#define CONSTRUCT_POLYGON_HXX_INCLUDED

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Gps_circle_segment_traits_2.h>
#include <CGAL/General_polygon_set_2.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2                                   K_Point_2;
typedef Kernel::Circle_2                                  K_Circle_2;
typedef CGAL::Gps_circle_segment_traits_2<Kernel>         Traits_2; /* The traits class Gps_circle_segment_traits_2 models the GeneralPolygonSetTraits_2 concept.
                                                                     * It enables Boolean set-operations on general polygons bounded by linear segments or circular arcs. It should be parameterized with a kernel. */
typedef CGAL::General_polygon_set_2<Traits_2>             Polygon_set_2;
typedef Traits_2::General_polygon_2                       Polygon_2;
typedef Traits_2::General_polygon_with_holes_2            Polygon_with_holes_2;
typedef Traits_2::Curve_2                                 Curve_2;
typedef Traits_2::X_monotone_curve_2                      X_monotone_curve_2;
typedef Polygon_2::Point_2                                P_Point_2;
typedef Polygon_2::X_monotone_curve_2                     P_X_monotone_curve_2;
typedef Kernel::FT                                        FT;
typedef Kernel::RT                                        RT;
typedef Traits_2::CoordNT                                 coordnt;

void add_to_polygon (Polygon_2& pgn, const K_Point_2& source,
                     const K_Point_2& mid, const K_Point_2& target);    // Create and insert a circular arc into polygon
void add_to_polygon (Polygon_2& pgn, Curve_2& circular_arc);
Polygon_2 construct_polygon (const K_Circle_2& circle);                 // Create circular polygon
Polygon_2 construct_polygon (const K_Point_2& p1, const K_Point_2& p2,  // Create polygon between the four points
                             const K_Point_2& p3, const K_Point_2& p4);

#endif // CONSTRUCT_POLYGON_HXX_INCLUDED