Joining several polygons

polys.cpp

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Polygon_2.h>
#include <CGAL/Polygon_with_holes_2.h>
#include <CGAL/Boolean_set_operations_2.h>
#include <CGAL/IO/WKT.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2                    Point_2;
typedef CGAL::Polygon_2<Kernel>            Polygon_2;
typedef CGAL::Polygon_with_holes_2<Kernel> Polygon_with_holes_2;

int main()
{
  // Read the polygons from WTK file
  std::ifstream is("polys.txt");
  std::list<Polygon_2> polys;
  int ccw = 0, cw = 0;
  ;
  do {
    Polygon_2 p;
    CGAL::IO::read_polygon_WKT(is, p);

    std::cout << p << std::endl << std::endl;
    if(!p.is_empty()){
      assert(p.is_simple());
      if(p.is_counterclockwise_oriented()){
        ccw++;
      }
      if(p.is_clockwise_oriented()){
        cw++;
        p.reverse_orientation();
      }
      polys.push_back(p);
    }
  } while(is.good() && !is.eof());

  std::cout << ccw << "  " << cw << std::endl;

  // Join the polygons
  std::deque<Polygon_with_holes_2> result;
  CGAL::join(polys.begin(), polys.end(), std::back_inserter(result));

  for(const Polygon_with_holes_2& p : result)
    {
      if(p.outer_boundary().is_empty()){
        std::cout << "outer boundary is empty" << std::endl;
        continue;
      }
      assert(p.outer_boundary().is_counterclockwise_oriented());

      for(Polygon_with_holes_2::Hole_const_iterator h_it =
            p.holes_begin(); h_it != p.holes_end(); ++h_it)
        {
          std::cout << "a hole" << std::endl;
          assert(h_it->is_clockwise_oriented());
        }
    }

  std::ofstream out("out.wkt");
  out.precision(17);
  CGAL::IO::write_multi_polygon_WKT(out, result);

  return 0;
}