1 // Ceres Solver - A fast non-linear least squares minimizer
2 // Copyright 2015 Google Inc. All rights reserved.
3 // http://ceres-solver.org/
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29 // Author: sameeragarwal@google.com (Sameer Agarwal)
31 // An implementation of the Canonical Views clustering algorithm from
32 // "Scene Summarization for Online Image Collections", Ian Simon, Noah
33 // Snavely, Steven M. Seitz, ICCV 2007.
35 // More details can be found at
36 // http://grail.cs.washington.edu/projects/canonview/
38 // Ceres uses this algorithm to perform view clustering for
39 // constructing visibility based preconditioners.
41 #ifndef CERES_INTERNAL_CANONICAL_VIEWS_CLUSTERING_H_
42 #define CERES_INTERNAL_CANONICAL_VIEWS_CLUSTERING_H_
46 #include "ceres/collections_port.h"
47 #include "ceres/graph.h"
52 struct CanonicalViewsClusteringOptions;
54 // Compute a partitioning of the vertices of the graph using the
55 // canonical views clustering algorithm.
57 // In the following we will use the terms vertices and views
58 // interchangably. Given a weighted Graph G(V,E), the canonical views
59 // of G are the the set of vertices that best "summarize" the content
60 // of the graph. If w_ij i s the weight connecting the vertex i to
61 // vertex j, and C is the set of canonical views. Then the objective
62 // of the canonical views algorithm is
64 // E[C] = sum_[i in V] max_[j in C] w_ij
65 // - size_penalty_weight * |C|
66 // - similarity_penalty_weight * sum_[i in C, j in C, j > i] w_ij
68 // alpha is the size penalty that penalizes large number of canonical
71 // beta is the similarity penalty that penalizes canonical views that
72 // are too similar to other canonical views.
74 // Thus the canonical views algorithm tries to find a canonical view
75 // for each vertex in the graph which best explains it, while trying
76 // to minimize the number of canonical views and the overlap between
79 // We further augment the above objective function by allowing for per
80 // vertex weights, higher weights indicating a higher preference for
81 // being chosen as a canonical view. Thus if w_i is the vertex weight
82 // for vertex i, the objective function is then
84 // E[C] = sum_[i in V] max_[j in C] w_ij
85 // - size_penalty_weight * |C|
86 // - similarity_penalty_weight * sum_[i in C, j in C, j > i] w_ij
87 // + view_score_weight * sum_[i in C] w_i
89 // centers will contain the vertices that are the identified
90 // as the canonical views/cluster centers, and membership is a map
91 // from vertices to cluster_ids. The i^th cluster center corresponds
92 // to the i^th cluster.
94 // It is possible depending on the configuration of the clustering
95 // algorithm that some of the vertices may not be assigned to any
96 // cluster. In this case they are assigned to a cluster with id = -1;
97 void ComputeCanonicalViewsClustering(
98 const CanonicalViewsClusteringOptions& options,
99 const WeightedGraph<int>& graph,
100 std::vector<int>* centers,
101 HashMap<int, int>* membership);
103 struct CanonicalViewsClusteringOptions {
104 CanonicalViewsClusteringOptions()
106 size_penalty_weight(5.75),
107 similarity_penalty_weight(100.0),
108 view_score_weight(0.0) {
110 // The minimum number of canonical views to compute.
113 // Penalty weight for the number of canonical views. A higher
114 // number will result in fewer canonical views.
115 double size_penalty_weight;
117 // Penalty weight for the diversity (orthogonality) of the
118 // canonical views. A higher number will encourage less similar
120 double similarity_penalty_weight;
122 // Weight for per-view scores. Lower weight places less
123 // confidence in the view scores.
124 double view_score_weight;
127 } // namespace internal
130 #endif // CERES_INTERNAL_CANONICAL_VIEWS_CLUSTERING_H_