The example itself

Spatial_searching/examples/Spatial_searching/searching_triangulation_vertices.cpp

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+#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
+#include <CGAL/Search_traits_3.h>
+#include <CGAL/Search_traits_adapter.h>
+#include <CGAL/Orthogonal_k_neighbor_search.h>
+#include <CGAL/Delaunay_triangulation_3.h>
+#include <CGAL/function_objects.h>
+
+#include <boost/property_map/function_property_map.hpp>
+
+#include <fstream>
+
+typedef CGAL::Exact_predicates_inexact_constructions_kernel Kernel;
+typedef Kernel::Point_3 Point_3;
+typedef CGAL::Delaunay_triangulation_3<Kernel> Delaunay;
+typedef Delaunay::Vertex_handle Vertex_handle;
+
+
+struct Project {
+  typedef Vertex_handle   argument_type;
+  typedef const Point_3&  Point;
+  typedef Point           result_type;
+  const Point& operator()( Vertex_handle  v) const { return v->point(); }
+};
+
+
+typedef boost::function_property_map<Project, Vertex_handle> Vertex_point_pmap;
+typedef CGAL::Search_traits_3<Kernel>                        Traits_base;
+typedef CGAL::Search_traits_adapter<Vertex_handle,Vertex_point_pmap,Traits_base> Traits;
+typedef CGAL::Orthogonal_k_neighbor_search<Traits>                               K_neighbor_search;
+typedef K_neighbor_search::Tree                                                  Tree;
+typedef Tree::Splitter                                                           Splitter;
+typedef K_neighbor_search::Distance                                              Distance;
+
+int main(int argc, char* argv[])
+{
+  std::ifstream in((argc>1)?argv[1]:CGAL::data_file_path("points_3/kitten.xyz"));
+  std::vector<Point_3> points;
+  Point_3 p;
+  while(in >> p){
+    points.push_back(p);
+  }
+
+  Delaunay dt(points.begin(), points.end());
+
+  const unsigned int K = 5;
+
+  Project project;
+  Vertex_point_pmap vppmap(project);
+
+  // Insert number_of_data_points in the tree
+  Tree tree(dt.finite_vertex_handles().begin(), dt.finite_vertex_handles().end(), Splitter(), Traits(vppmap));
+
+  // search K nearest neighbors
+  Point_3 query(0.0, 0.0, 0.0);
+  Distance tr_dist(vppmap);
+
+  K_neighbor_search search(tree, query, K,0,true,tr_dist);
+  std::cout <<"The "<< K << " nearest vertices to the query point at (0,0,0) are:" << std::endl;
+  for(K_neighbor_search::iterator it = search.begin(); it != search.end(); it++){
+    std::cout << "vertex " << &*(it->first) << " : " << vppmap[it->first] << " at distance "
+              << tr_dist.inverse_of_transformed_distance(it->second) << std::endl;
+  }
+
+  return 0;
+}