Question

我对CGAL::do_intersect的工作方式感到有些困惑。如果两个多边形中都有一个点，我认为该函数返回true。至于我没有弄错in位于out内，我应该看到true打印出来或者我错过了什么？

#include <CGAL/Point_2.h>
#include <CGAL/Polygon_2.h>
#include <CGAL/Exact_predicates_exact_constructions_kernel.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2 Point_2;
typedef CGAL::Polygon_2<Kernel> Polygon_2;
int main(int argc, char **argv)
{
  Polygon_2 in, out;
  in.push_back(Point_2(1,1));
  in.push_back(Point_2(1,2));
  in.push_back(Point_2(2,2));
  in.push_back(Point_2(2,1));

  out.push_back(Point_2(0,0));
  out.push_back(Point_2(3,0));
  out.push_back(Point_2(3,3));
  out.push_back(Point_2(0,3));

  std::cout << "IN intersect with OUT is " << (CGAL::do_intersect(in, out) ? "true":"false") << std::endl;
  std::cout << "OUT intersect with IN is " << (CGAL::do_intersect(out, in) ? "true":"false") << std::endl;
  std::cout.flush();
}

Answer 1

多边形中的顶点需要逆时针。以下代码生成所需的输出：

IN intersect with OUT is true
OUT intersect with IN is true

#include <CGAL/Point_2.h>
#include <CGAL/Polygon_2.h>
#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Boolean_set_operations_2.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
typedef Kernel::Point_2 Point_2;
typedef CGAL::Polygon_2<Kernel> Polygon_2;
int main(int argc, char **argv)
{
  Polygon_2 in, out;
  in.push_back(Point_2(1,1));
  in.push_back(Point_2(2,1));
  in.push_back(Point_2(2,2));
  in.push_back(Point_2(1,2));

  out.push_back(Point_2(0,0));
  out.push_back(Point_2(3,0));
  out.push_back(Point_2(3,3));
  out.push_back(Point_2(0,3));

  std::cout << "IN intersect with OUT is " << (CGAL::do_intersect(in, out) ? "true":"false") << std::endl;
  std::cout << "OUT intersect with IN is " << (CGAL::do_intersect(out, in) ? "true":"false") << std::endl;
  std::cout.flush();
}

CGAL Intersection返回false结果

1 个答案: