[37] | 1 | /* |
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| 2 | Copyright (C) 2006 Pedro Felzenszwalb |
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| 3 | |
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| 4 | This program is free software; you can redistribute it and/or modify |
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| 5 | it under the terms of the GNU General Public License as published by |
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| 6 | the Free Software Foundation; either version 2 of the License, or |
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| 7 | (at your option) any later version. |
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| 8 | |
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| 9 | This program is distributed in the hope that it will be useful, |
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| 10 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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| 12 | GNU General Public License for more details. |
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| 13 | |
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| 14 | You should have received a copy of the GNU General Public License |
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| 15 | along with this program; if not, write to the Free Software |
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| 16 | Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA |
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| 17 | */ |
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| 18 | |
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| 19 | #ifndef SEGMENT_GRAPH |
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| 20 | #define SEGMENT_GRAPH |
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| 21 | |
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| 22 | #include <algorithm> |
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| 23 | #include <cmath> |
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| 24 | #include "disjoint-set.h" |
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| 25 | |
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| 26 | // threshold function |
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| 27 | #define THRESHOLD(size, c) (c/size) |
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| 28 | |
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| 29 | typedef struct { |
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| 30 | float w; |
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| 31 | int a, b; |
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| 32 | } edge; |
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| 33 | |
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| 34 | bool operator<(const edge &a, const edge &b) { |
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| 35 | return a.w < b.w; |
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| 36 | } |
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| 37 | |
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| 38 | /* |
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| 39 | * Segment a graph |
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| 40 | * |
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| 41 | * Returns a disjoint-set forest representing the segmentation. |
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| 42 | * |
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| 43 | * num_vertices: number of vertices in graph. |
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| 44 | * num_edges: number of edges in graph |
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| 45 | * edges: array of edges. |
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| 46 | * c: constant for treshold function. |
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| 47 | */ |
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| 48 | universe *segment_graph(int num_vertices, int num_edges, edge *edges, |
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| 49 | float c) { |
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| 50 | // sort edges by weight |
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| 51 | std::sort(edges, edges + num_edges); |
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| 52 | |
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| 53 | // make a disjoint-set forest |
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| 54 | universe *u = new universe(num_vertices); |
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| 55 | |
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| 56 | // init thresholds |
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| 57 | float *threshold = new float[num_vertices]; |
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| 58 | for (int i = 0; i < num_vertices; i++) |
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| 59 | threshold[i] = THRESHOLD(1,c); |
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| 60 | |
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| 61 | // for each edge, in non-decreasing weight order... |
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| 62 | for (int i = 0; i < num_edges; i++) { |
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| 63 | edge *pedge = &edges[i]; |
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| 64 | |
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| 65 | // components conected by this edge |
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| 66 | int a = u->find(pedge->a); |
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| 67 | int b = u->find(pedge->b); |
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| 68 | if (a != b) { |
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| 69 | if ((pedge->w <= threshold[a]) && |
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| 70 | (pedge->w <= threshold[b])) { |
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| 71 | u->join(a, b); |
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| 72 | a = u->find(a); |
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| 73 | threshold[a] = pedge->w + THRESHOLD(u->size(a), c); |
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| 74 | } |
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| 75 | } |
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| 76 | } |
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| 77 | |
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| 78 | // free up |
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| 79 | delete threshold; |
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| 80 | return u; |
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| 81 | } |
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| 82 | |
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| 83 | #endif |
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