如何使用CGAL获得2D alpha形状后的剩余三角形？

#include <iostream>
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Delaunay_triangulation_2.h>
#include <CGAL/Alpha_shape_2.h>

typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Alpha_shape_vertex_base_2<K>               Vb;
typedef CGAL::Alpha_shape_face_base_2<K>                 Fb;
typedef CGAL::Triangulation_data_structure_2<Vb,Fb>      Tds;
typedef CGAL::Delaunay_triangulation_2<K,Tds>            Delaunay;
typedef CGAL::Alpha_shape_2<Delaunay>                    Alpha_shape_2;

int main()
{
  std::vector<K::Point_2> points;

  // 添加点到点集
  points.push_back(K::Point_2(0, 0));
  points.push_back(K::Point_2(1, 0));
  points.push_back(K::Point_2(0, 1));

  // 创建Delaunay三角剖分
  Delaunay triangulation;
  triangulation.insert(points.begin(), points.end());

  // 创建alpha形状
  Alpha_shape_2 alpha_shape(triangulation);

  // 设置alpha值
  double alpha = 0.1;
  alpha_shape.set_alpha(alpha);

  // 提取剩余三角形
  std::vector<Alpha_shape_2::Facet> facets;
  alpha_shape.get_alpha_shape_facets(std::back_inserter(facets), Alpha_shape_2::REGULAR);

  // 输出结果
  for(auto facet : facets) {
    std::cout << "Facet: " << alpha_shape.classify(facet) << std::endl;
  }

  return 0;
}