CGAL 6.1.2 - 2D Alpha Shapes

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Alpha_shapes_2/ex_periodic_alpha_shapes_2.cpp
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
#include <CGAL/Periodic_2_Delaunay_triangulation_traits_2.h>
#include <CGAL/Periodic_2_Delaunay_triangulation_2.h>
#include <CGAL/Alpha_shape_2.h>
#include <CGAL/Alpha_shape_face_base_2.h>
#include <CGAL/Alpha_shape_vertex_base_2.h>
#include <fstream>
#include <iostream>
// Traits
typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
typedef CGAL::Periodic_2_Delaunay_triangulation_traits_2<K> Gt;
// Vertex type
typedef CGAL::Periodic_2_triangulation_vertex_base_2<Gt> Vb;
typedef CGAL::Alpha_shape_vertex_base_2<Gt, Vb> AsVb;
// Cell type
typedef CGAL::Periodic_2_triangulation_face_base_2<Gt> Cb;
typedef CGAL::Alpha_shape_face_base_2<Gt, Cb> AsCb;
typedef CGAL::Triangulation_data_structure_2<AsVb, AsCb> Tds;
typedef CGAL::Periodic_2_Delaunay_triangulation_2<Gt, Tds> P2DT2;
typedef CGAL::Alpha_shape_2<P2DT2> Alpha_shape_2;
typedef Gt::Point_2 Point;
typedef Gt::Segment_2 Segment;
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;
std::copy_n(std::istream_iterator<Point>(is), n, out);
return true;
}
int main()
{
std::list<Point> points;
if(! file_input(std::back_inserter(points)))
return -1;
// Define the periodic square
P2DT2 pdt(Gt::Iso_rectangle_2(-10,-10, 700,700));
// Heuristic for inserting large point sets (if pts is reasonably large)
pdt.insert(points.begin(), points.end(), true);
// As pdt won't be modified anymore switch to 1-sheeted cover if possible
if(pdt.is_triangulation_in_1_sheet())
pdt.convert_to_1_sheeted_covering();
std::cout << "Periodic Delaunay computed." << std::endl;
// compute alpha shape
Alpha_shape_2 as(pdt);
std::cout << "Alpha shape computed in REGULARIZED mode by default." << std::endl;
// find optimal alpha values
Alpha_shape_2::NT alpha_solid = as.find_alpha_solid();
Alpha_shape_2::Alpha_iterator opt = as.find_optimal_alpha(1);
std::cout << "Smallest alpha value to get a solid through data points is " << alpha_solid << std::endl;
std::cout << "Optimal alpha value to get one connected component is " << *opt << std::endl;
as.set_alpha(*opt);
assert(as.number_of_solid_components() == 1);
as.set_alpha(10000);
std::vector<Segment> segments;
alpha_edges(as, std::back_inserter(segments));
std::cout << segments.size() << " alpha shape edges" << std::endl;
return 0;
}
CGAL::Alpha_shape_2
The class Alpha_shape_2 represents the family of -shapes of points in a plane for all positive .
Definition: Alpha_shape_2.h:87
CGAL::Alpha_shape_2::alpha_shape_edges_begin
Alpha_shape_edges_iterator alpha_shape_edges_begin()
Starts at an arbitrary finite edge which belongs to the -shape for the current .
CGAL::Alpha_shape_face_base_2
The class Alpha_shape_face_base_2 is the default model for the concept AlphaShapeFace_2.
Definition: Alpha_shape_face_base_2.h:26
CGAL::Alpha_shape_vertex_base_2
The class Alpha_shape_vertex_base_2 is the default model for the concept AlphaShapeVertex_2.
Definition: Alpha_shape_vertex_base_2.h:27
CGAL::Exact_predicates_inexact_constructions_kernel
CGAL::Periodic_2_Delaunay_triangulation_2
CGAL::Periodic_2_Delaunay_triangulation_traits_2
CGAL::Periodic_2_triangulation_face_base_2
CGAL::Periodic_2_triangulation_vertex_base_2
OutputIterator