1 // Ceres Solver - A fast non-linear least squares minimizer
2 // Copyright 2010, 2011, 2012 Google Inc. All rights reserved.
3 // http://code.google.com/p/ceres-solver/
4 //
5 // Redistribution and use in source and binary forms, with or without
6 // modification, are permitted provided that the following conditions are met:
7 //
8 // * Redistributions of source code must retain the above copyright notice,
9 // this list of conditions and the following disclaimer.
10 // * Redistributions in binary form must reproduce the above copyright notice,
11 // this list of conditions and the following disclaimer in the documentation
12 // and/or other materials provided with the distribution.
13 // * Neither the name of Google Inc. nor the names of its contributors may be
14 // used to endorse or promote products derived from this software without
15 // specific prior written permission.
16 //
17 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
21 // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22 // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23 // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24 // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25 // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26 // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27 // POSSIBILITY OF SUCH DAMAGE.
28 //
29 // Author: kushalav@google.com (Avanish Kushal)
30
31 // This include must come before any #ifndef check on Ceres compile options.
32 #include "ceres/internal/port.h"
33
34 #ifndef CERES_NO_SUITESPARSE
35
36 #include "ceres/visibility.h"
37
38 #include <cmath>
39 #include <ctime>
40 #include <algorithm>
41 #include <set>
42 #include <vector>
43 #include <utility>
44 #include "ceres/block_structure.h"
45 #include "ceres/collections_port.h"
46 #include "ceres/graph.h"
47 #include "glog/logging.h"
48
49 namespace ceres {
50 namespace internal {
51
ComputeVisibility(const CompressedRowBlockStructure & block_structure,const int num_eliminate_blocks,vector<set<int>> * visibility)52 void ComputeVisibility(const CompressedRowBlockStructure& block_structure,
53 const int num_eliminate_blocks,
54 vector< set<int> >* visibility) {
55 CHECK_NOTNULL(visibility);
56
57 // Clear the visibility vector and resize it to hold a
58 // vector for each camera.
59 visibility->resize(0);
60 visibility->resize(block_structure.cols.size() - num_eliminate_blocks);
61
62 for (int i = 0; i < block_structure.rows.size(); ++i) {
63 const vector<Cell>& cells = block_structure.rows[i].cells;
64 int block_id = cells[0].block_id;
65 // If the first block is not an e_block, then skip this row block.
66 if (block_id >= num_eliminate_blocks) {
67 continue;
68 }
69
70 for (int j = 1; j < cells.size(); ++j) {
71 int camera_block_id = cells[j].block_id - num_eliminate_blocks;
72 DCHECK_GE(camera_block_id, 0);
73 DCHECK_LT(camera_block_id, visibility->size());
74 (*visibility)[camera_block_id].insert(block_id);
75 }
76 }
77 }
78
CreateSchurComplementGraph(const vector<set<int>> & visibility)79 Graph<int>* CreateSchurComplementGraph(const vector<set<int> >& visibility) {
80 const time_t start_time = time(NULL);
81 // Compute the number of e_blocks/point blocks. Since the visibility
82 // set for each e_block/camera contains the set of e_blocks/points
83 // visible to it, we find the maximum across all visibility sets.
84 int num_points = 0;
85 for (int i = 0; i < visibility.size(); i++) {
86 if (visibility[i].size() > 0) {
87 num_points = max(num_points, (*visibility[i].rbegin()) + 1);
88 }
89 }
90
91 // Invert the visibility. The input is a camera->point mapping,
92 // which tells us which points are visible in which
93 // cameras. However, to compute the sparsity structure of the Schur
94 // Complement efficiently, its better to have the point->camera
95 // mapping.
96 vector<set<int> > inverse_visibility(num_points);
97 for (int i = 0; i < visibility.size(); i++) {
98 const set<int>& visibility_set = visibility[i];
99 for (set<int>::const_iterator it = visibility_set.begin();
100 it != visibility_set.end();
101 ++it) {
102 inverse_visibility[*it].insert(i);
103 }
104 }
105
106 // Map from camera pairs to number of points visible to both cameras
107 // in the pair.
108 HashMap<pair<int, int>, int > camera_pairs;
109
110 // Count the number of points visible to each camera/f_block pair.
111 for (vector<set<int> >::const_iterator it = inverse_visibility.begin();
112 it != inverse_visibility.end();
113 ++it) {
114 const set<int>& inverse_visibility_set = *it;
115 for (set<int>::const_iterator camera1 = inverse_visibility_set.begin();
116 camera1 != inverse_visibility_set.end();
117 ++camera1) {
118 set<int>::const_iterator camera2 = camera1;
119 for (++camera2; camera2 != inverse_visibility_set.end(); ++camera2) {
120 ++(camera_pairs[make_pair(*camera1, *camera2)]);
121 }
122 }
123 }
124
125 Graph<int>* graph = new Graph<int>();
126
127 // Add vertices and initialize the pairs for self edges so that self
128 // edges are guaranteed. This is needed for the Canonical views
129 // algorithm to work correctly.
130 static const double kSelfEdgeWeight = 1.0;
131 for (int i = 0; i < visibility.size(); ++i) {
132 graph->AddVertex(i);
133 graph->AddEdge(i, i, kSelfEdgeWeight);
134 }
135
136 // Add an edge for each camera pair.
137 for (HashMap<pair<int, int>, int>::const_iterator it = camera_pairs.begin();
138 it != camera_pairs.end();
139 ++it) {
140 const int camera1 = it->first.first;
141 const int camera2 = it->first.second;
142 CHECK_NE(camera1, camera2);
143
144 const int count = it->second;
145 // Static cast necessary for Windows.
146 const double weight = static_cast<double>(count) /
147 (sqrt(static_cast<double>(
148 visibility[camera1].size() * visibility[camera2].size())));
149 graph->AddEdge(camera1, camera2, weight);
150 }
151
152 VLOG(2) << "Schur complement graph time: " << (time(NULL) - start_time);
153 return graph;
154 }
155
156 } // namespace internal
157 } // namespace ceres
158
159 #endif // CERES_NO_SUITESPARSE
160