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GetFEM: src/getfem/bgeot_kdtree.h Source File
GetFEM  5.4.2
bgeot_kdtree.h
Go to the documentation of this file.
1 /* -*- c++ -*- (enables emacs c++ mode) */
2 /*===========================================================================
3 
4  Copyright (C) 2004-2020 Julien Pommier
5 
6  This file is a part of GetFEM
7 
8  GetFEM is free software; you can redistribute it and/or modify it
9  under the terms of the GNU Lesser General Public License as published
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11  (at your option) any later version along with the GCC Runtime Library
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20 
21  As a special exception, you may use this file as it is a part of a free
22  software library without restriction. Specifically, if other files
23  instantiate templates or use macros or inline functions from this file,
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29 
30 ===========================================================================*/
31 
32 #ifndef BGEOT_KDTREE_H
33 #define BGEOT_KDTREE_H
34 
35 /** @file bgeot_kdtree.h
36  @author Julien Pommier <Julien.Pommier@insa-toulouse.fr>
37  @date January 2004.
38  @brief Simple implementation of a KD-tree.
39 
40  Basically, a KD-tree is a balanced N-dimensional tree.
41 */
42 #include "bgeot_small_vector.h"
43 
44 namespace bgeot {
45 
46  /* generic node for the kdtree */
47  struct kdtree_elt_base {
48  enum { PTS_PER_LEAF=8 };
49  unsigned n; /* 0 => is a tree node, != 0 => tree leaf storing n points */
50  bool isleaf() const { return (n != 0); }
51  kdtree_elt_base(unsigned n_) : n(n_) {}
52  virtual ~kdtree_elt_base() {}
53  };
54 
55  /// store a point and the associated index for the kdtree.
56  /* std::pair<size_type,base_node> is not ok since it does not
57  have a suitable overloaded swap function ...
58  */
59  struct index_node_pair {
60  size_type i;
61  base_node n;
62  index_node_pair() {}
63  index_node_pair(size_type i_, base_node n_) : i(i_), n(n_) {}
64  void swap(index_node_pair& other) { std::swap(i,other.i); n.swap(other.n);}
65  };
66 
67  /// store a set of points with associated indexes.
68  typedef std::vector<index_node_pair> kdtree_tab_type;
69 
70  /** Balanced tree over a set of points.
71 
72  Once the tree have been built, it is possible to query very
73  quickly for the list of points lying in a given box. Note that
74  this is not a dynamic structure: once you start to call
75  kdtree::points_in_box, you should not use anymore kdtree::add_point.
76 
77  Here is an example of use (which tries to find the mapping between
78  the dof of the mesh_fem and the node numbers of its mesh):
79 
80  @code
81  void dof_to_nodes(const getfem::mesh_fem &mf) {
82  const getfem::getfem_mesh &m = mf.linked_mesh();
83  bgeot::kdtree tree;
84  for (dal::bv_visitor ip(m.points().index()); !ip.finished(); ++ip) {
85  tree.add_point_with_id(m.points()[ip], ip);
86  }
87  bgeot::kdtree_tab_type t;
88  for (size_type d = 0; d < mf.nb_dof(); ++d) {
89  getfem::base_node P(mf.point_of_dof(d)), P2(P);
90  for (unsigned i=0; i < P.size(); ++i) {
91  P[i] -= 1e-12; P2[i]+= 1e-12;
92  }
93  tree.points_in_box(t, P, P2);
94  if (t.size()) {
95  assert(t.size() == 1);
96  cout << " dof " << d << " maps to mesh node " << t[0].i << "\n";
97  }
98  }
99  }
100  @endcode
101  */
102  class kdtree {
103  dim_type N; /* dimension of points */
104  std::unique_ptr<kdtree_elt_base> tree;
105  kdtree_tab_type pts;
106  public:
107  kdtree() : N(0) {}
108 
109  kdtree(const kdtree&) = delete;
110  kdtree &operator = (const kdtree&) = delete;
111 
112  /// reset the tree, remove all points
113  void clear() { clear_tree(); pts = kdtree_tab_type(); N = 0; }
114  void reserve(size_type n) { pts.reserve(n); }
115  /// insert a new point
117  size_type i = pts.size(); add_point_with_id(n,i); return i;
118  }
119  /// insert a new point, with an associated number.
121  if (pts.size() == 0)
122  N = n.size();
123  else
124  GMM_ASSERT2(N == n.size(), "invalid dimension");
125  if (tree) clear_tree();
126  pts.push_back(index_node_pair(i, n));
127  }
128  size_type nb_points() const { return pts.size(); }
129  const kdtree_tab_type &points() const { return pts; }
130  /* fills ipts with the indexes of points in the box
131  [min,max] */
132  void points_in_box(kdtree_tab_type &ipts,
133  const base_node &min,
134  const base_node &max);
135  /* assigns at ipt the index of the nearest neighbor at location
136  pos and returns the square of the distance to this point*/
137  scalar_type nearest_neighbor(index_node_pair &ipt,
138  const base_node &pos);
139  private:
140  typedef std::vector<size_type>::const_iterator ITER;
141  void clear_tree();
142  };
143 }
144 
145 #endif
bgeot::kdtree_tab_type
std::vector< index_node_pair > kdtree_tab_type
store a set of points with associated indexes.
Definition: bgeot_kdtree.h:68
bgeot::size_type
size_t size_type
used as the common size type in the library
Definition: bgeot_poly.h:49
bgeot::kdtree::add_point
size_type add_point(const base_node &n)
insert a new point
Definition: bgeot_kdtree.h:116
bgeot::kdtree
Balanced tree over a set of points.
Definition: bgeot_kdtree.h:102
bgeot::kdtree::clear
void clear()
reset the tree, remove all points
Definition: bgeot_kdtree.h:113
bgeot::small_vector< scalar_type >
bgeot_small_vector.h
Small (dim < 8) vectors.
bgeot
Basic Geometric Tools.
Definition: bgeot_convex_ref.cc:27
bgeot::index_node_pair
store a point and the associated index for the kdtree.
Definition: bgeot_kdtree.h:59
bgeot::kdtree::add_point_with_id
void add_point_with_id(const base_node &n, size_type i)
insert a new point, with an associated number.
Definition: bgeot_kdtree.h:120