Alpha_shapes_2/ex_alpha_shapes_2.cpp

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

#include <iostream>
#include <fstream>
#include <vector>
#include <list>

typedef CGAL::Exact_predicates_inexact_constructions_kernel  K;

typedef K::FT                                                FT;
typedef K::Point_2                                           Point;
typedef K::Segment_2                                         Segment;

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>                Triangulation_2;
typedef CGAL::Alpha_shape_2<Triangulation_2>                 Alpha_shape_2;

typedef Alpha_shape_2::Alpha_shape_edges_iterator            Alpha_shape_edges_iterator;

template <class OutputIterator>
void alpha_edges( const Alpha_shape_2& A, OutputIterator out)
{
  Alpha_shape_edges_iterator it = A.alpha_shape_edges_begin(),
                             end = A.alpha_shape_edges_end();
  for( ; it!=end; ++it)
    *out++ = A.segment(*it);
}

template <class OutputIterator>
bool file_input(OutputIterator out)
{
  std::ifstream is("./data/fin", std::ios::in);

  if(is.fail())
  {
    std::cerr << "unable to open file for input" << std::endl;
    return false;
  }

  int n;
  is >> n;
  std::cout << "Reading " << n << " points from file" << std::endl;
  CGAL::cpp11::copy_n(std::istream_iterator<Point>(is), n, out);

  return true;
}

// Reads a list of points and returns a list of segments
// corresponding to the Alpha shape.
int main()
{
  std::list<Point> points;
  if(! file_input(std::back_inserter(points)))
    return -1;

  Alpha_shape_2 A(points.begin(), points.end(),
                  FT(10000),
                  Alpha_shape_2::GENERAL);

  std::vector<Segment> segments;
  alpha_edges(A, std::back_inserter(segments));

  std::cout << "Alpha Shape computed" << std::endl;
  std::cout << segments.size() << " alpha shape edges" << std::endl;
  std::cout << "Optimal alpha: " << *A.find_optimal_alpha(1)<<std::endl;

  return 0;
}