Join two polygons

join.cpp

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Boolean_set_operations_2.h>
#include <list>
#include <CGAL/Polygon_2.h>
#include <CGAL/IO/WKT.h>
#include <iostream>
#include <fstream>

typedef CGAL::Exact_predicates_exact_constructions_kernel K;
typedef K::Point_2                                        Point;
typedef CGAL::Polygon_2<K>                                Polygon_2;
typedef CGAL::Polygon_with_holes_2<K>                     Polygon_with_holes_2;
typedef std::vector<Polygon_with_holes_2>                 Pwh_list_2;



int main(int argc, char* argv[])
{
  std::ifstream is(argv[1]);
  Pwh_list_2 polys;

  do {
      Polygon_with_holes_2 p;
      CGAL::IO::read_polygon_WKT(is, p);
      if (!p.outer_boundary().is_empty()) {
        assert(p.outer_boundary().is_counterclockwise_oriented());
        assert(p.outer_boundary().is_simple());
        polys.push_back(p);
      }
  }while(is.good() && !is.eof());


  Pwh_list_2 unionR;



  CGAL::join(std::begin(polys), std::end(polys), std::back_inserter(unionR));

  CGAL::IO::write_multi_polygon_WKT(std::cout, unionR);

  return 0;
}

two.wkt

POLYGON(( 0 0, 1 0, 1 1, 0 1 ))
POLYGON(( 1 1, 2 1, 2 2, 1 2 ))

The output is a single polygon. We pass two times at (1,1) but is is a pinching point, but not an intersection