1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
|
/**
* Copyright (C) 2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kQuery
#include "mongo/platform/basic.h"
#include "mongo/db/geo/shapes.h"
#include "mongo/db/geo/r2_region_coverer.h"
#include "mongo/util/log.h"
namespace mongo {
// Definition
int const R2RegionCoverer::kDefaultMaxCells = 8;
// We define our own own comparison function on QueueEntries in order to
// make the results deterministic. Using the default less<QueueEntry>,
// entries of equal priority would be sorted according to the memory address
// of the candidate.
struct R2RegionCoverer::CompareQueueEntries : public less<QueueEntry> {
bool operator()(QueueEntry const& x, QueueEntry const& y) {
return x.first < y.first;
}
};
// Doesn't take ownership of "hashConverter". The caller should guarantee its life cycle
// is longer than this coverer.
R2RegionCoverer::R2RegionCoverer( GeoHashConverter* hashConverter ) :
_hashConverter( hashConverter ),
_minLevel( 0u ),
_maxLevel( GeoHash::kMaxBits ),
_maxCells( kDefaultMaxCells ),
_region( NULL ),
_candidateQueue( new CandidateQueue ),
_results( new vector<GeoHash> )
{
}
// Need to declare explicitly because of scoped pointers.
R2RegionCoverer::~R2RegionCoverer() { }
void R2RegionCoverer::setMinLevel( unsigned int minLevel ) {
dassert(minLevel >= 0);
dassert(minLevel <= GeoHash::kMaxBits);
_minLevel = max(0u, min(GeoHash::kMaxBits, minLevel));
}
void R2RegionCoverer::setMaxLevel( unsigned int maxLevel ) {
dassert(maxLevel >= 0);
dassert(maxLevel <= GeoHash::kMaxBits);
_maxLevel = max(0u, min(GeoHash::kMaxBits, maxLevel));
}
void R2RegionCoverer::setMaxCells( int maxCells ) {
_maxCells = maxCells;
}
void R2RegionCoverer::getCovering( const R2Region& region, vector<GeoHash>* cover ) {
// Strategy: Start with the full plane. Discard any
// that do not intersect the shape. Then repeatedly choose the
// largest cell that intersects the shape and subdivide it.
//
// _result contains the cells that will be part of the output, while the
// queue contains cells that we may still subdivide further. Cells that
// are entirely contained within the region are immediately added to the
// output, while cells that do not intersect the region are immediately
// discarded. Therefore the queue only contains cells that partially
// intersect the region. Candidates are prioritized first according to
// cell size (larger cells first), then by the number of intersecting
// children they have (fewest children first), and then by the number of
// fully contained children (fewest children first).
verify(_minLevel <= _maxLevel);
dassert(_candidateQueue->empty());
dassert(_results->empty());
_region = ®ion;
getInitialCandidates();
while(!_candidateQueue->empty()) {
Candidate* candidate = _candidateQueue->top().second; // Owned
_candidateQueue->pop();
LOG(3) << "Pop: " << candidate->cell;
// Try to expand this cell into its children
if (candidate->cell.getBits() < _minLevel ||
candidate->numChildren == 1 ||
(int)_results->size() +
(int)_candidateQueue->size() +
candidate->numChildren <= _maxCells) {
for (int i = 0; i < candidate->numChildren; i++) {
addCandidate(candidate->children[i]);
}
deleteCandidate(candidate, false);
} else {
// Reached max cells. Move all candidates from the queue into results.
candidate->isTerminal = true;
addCandidate(candidate);
}
LOG(3) << "Queue: " << _candidateQueue->size();
}
_region = NULL;
cover->swap(*_results);
}
// Caller owns the returned pointer
R2RegionCoverer::Candidate* R2RegionCoverer::newCandidate( const GeoHash& cell ) {
// Exclude the cell that doesn't intersect with the geometry.
Box box = _hashConverter->unhashToBoxCovering(cell);
if (_region->fastDisjoint(box)) {
return NULL;
}
Candidate* candidate = new Candidate();
candidate->cell = cell;
candidate->numChildren = 0;
// Stop subdivision when we reach the max level or there is no need to do so.
// Don't stop if we haven't reach min level.
candidate->isTerminal = cell.getBits() >= _minLevel &&
(cell.getBits() >= _maxLevel || _region->fastContains(box));
return candidate;
}
// Takes ownership of "candidate"
void R2RegionCoverer::addCandidate( Candidate* candidate ) {
if (candidate == NULL) return;
if (candidate->isTerminal) {
_results->push_back(candidate->cell);
deleteCandidate(candidate, true);
return;
}
verify(candidate->numChildren == 0);
// Expand children
int numTerminals = expandChildren(candidate);
if (candidate->numChildren == 0) {
deleteCandidate(candidate, true);
} else if (numTerminals == 4 && candidate->cell.getBits() >= _minLevel) {
// Optimization: add the parent cell rather than all of its children.
candidate->isTerminal = true;
addCandidate(candidate);
} else {
// Add the cell into the priority queue for further subdivision.
//
// We negate the priority so that smaller absolute priorities are returned
// first. The heuristic is designed to refine the largest cells first,
// since those are where we have the largest potential gain. Among cells
// at the same level, we prefer the cells with the smallest number of
// intersecting children. Finally, we prefer cells that have the smallest
// number of children that cannot be refined any further.
int priority = -(((((int)candidate->cell.getBits() << 4)
+ candidate->numChildren) << 4)
+ numTerminals);
_candidateQueue->push(make_pair(priority, candidate)); // queue owns candidate
LOG(3) << "Push: " << candidate->cell << " (" << priority << ") ";
}
}
// Dones't take ownership of "candidate"
int R2RegionCoverer::expandChildren( Candidate* candidate ) {
GeoHash childCells[4];
invariant(candidate->cell.subdivide(childCells));
int numTerminals = 0;
for (int i = 0; i < 4; ++i) {
Candidate* child = newCandidate(childCells[i]);
if (child) {
candidate->children[candidate->numChildren++] = child;
if (child->isTerminal) ++numTerminals;
}
}
return numTerminals;
}
// Takes ownership of "candidate"
void R2RegionCoverer::deleteCandidate( Candidate* candidate, bool freeChildren ) {
if (freeChildren) {
for (int i = 0; i < candidate->numChildren; i++) {
deleteCandidate(candidate->children[i], true);
}
}
delete candidate;
}
void R2RegionCoverer::getInitialCandidates() {
// Add the full plane
// TODO a better initialization.
addCandidate(newCandidate(GeoHash()));
}
//
// R2CellUnion
//
void R2CellUnion::init(const vector<GeoHash>& cellIds) {
_cellIds = cellIds;
normalize();
}
bool R2CellUnion::contains(const GeoHash cellId) const {
// Since all cells are ordered, if an ancestor of id exists, it must be the previous one.
vector<GeoHash>::const_iterator it;
it = upper_bound(_cellIds.begin(), _cellIds.end(), cellId); // it > cellId
return it != _cellIds.begin() && (--it)->contains(cellId); // --it <= cellId
}
bool R2CellUnion::normalize() {
vector<GeoHash> output;
output.reserve(_cellIds.size());
sort(_cellIds.begin(), _cellIds.end());
for (size_t i = 0; i < _cellIds.size(); i++) {
GeoHash id = _cellIds[i];
// Parent is less than children. If an ancestor of id exists, it must be the last one.
//
// Invariant: output doesn't contain intersected cells (ancestor and its descendants)
// Proof: Assume another cell "c" exists between ancestor "p" and the current "id",
// i.e. p < c < id, then "c" has "p" as its prefix, since id share the same prefix "p",
// so "p" contains "c", which conflicts with the invariant.
if (!output.empty() && output.back().contains(id)) continue;
// Check whether the last 3 elements of "output" plus "id" can be
// collapsed into a single parent cell.
while (output.size() >= 3) {
// A necessary (but not sufficient) condition is that the XOR of the
// four cells must be zero. This is also very fast to test.
if ((output.end()[-3].getHash() ^ output.end()[-2].getHash() ^ output.back().getHash())
!= id.getHash())
break;
// Now we do a slightly more expensive but exact test.
GeoHash parent = id.parent();
if (parent != output.end()[-3].parent() ||
parent != output.end()[-2].parent() ||
parent != output.end()[-1].parent())
break;
// Replace four children by their parent cell.
output.erase(output.end() - 3, output.end());
id = parent;
}
output.push_back(id);
}
if (output.size() < _cellIds.size()) {
_cellIds.swap(output);
return true;
}
return false;
}
string R2CellUnion::toString() const {
std::stringstream ss;
ss << "[ ";
for (size_t i = 0; i < _cellIds.size(); i++) {
ss << _cellIds[i] << " ";
}
ss << "]";
return ss.str();
}
} /* namespace mongo */
|