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/**
* 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.
*/
#pragma once
#include <queue>
#include "mongo/db/geo/hash.h"
namespace mongo {
class R2Region;
class R2RegionCoverer {
MONGO_DISALLOW_COPYING(R2RegionCoverer);
// By default, the covering uses at most 8 cells at any level.
static const int kDefaultMaxCells; // = 8;
public:
R2RegionCoverer() = default;
R2RegionCoverer(GeoHashConverter* hashConverter);
~R2RegionCoverer();
// Set the minimum and maximum cell level to be used. The default is to use
// all cell levels. Requires: max_level() >= min_level().
void setMinLevel(unsigned int minLevel);
void setMaxLevel(unsigned int maxLevel);
unsigned int minLevel() const {
return _minLevel;
}
unsigned int maxLevel() const {
return _maxLevel;
}
// Sets the maximum desired number of cells in the approximation (defaults
// to kDefaultMaxCells).
//
// For any setting of max_cells(), an arbitrary number of cells may be
// returned if min_level() is too high for the region being approximated.
//
// TODO(sz): accuracy experiments similar to S2RegionCoverer.
void setMaxCells(int maxCells);
int maxCells() const {
return _maxCells;
}
void getCovering(const R2Region& region, std::vector<GeoHash>* cover);
private:
struct Candidate {
GeoHash cell;
bool isTerminal; // Cell should not be expanded further.
int numChildren; // Number of children that intersect the region.
Candidate* children[4];
};
// If the cell intersects the given region, return a new candidate with no
// children, otherwise return NULL. Also marks the candidate as "terminal"
// if it should not be expanded further.
Candidate* newCandidate(GeoHash const& cell);
// Process a candidate by either adding it to the result_ vector or
// expanding its children and inserting it into the priority queue.
// Passing an argument of NULL does nothing.
void addCandidate(Candidate* candidate);
// Free the memory associated with a candidate.
void deleteCandidate(Candidate* candidate, bool freeChildren);
// Populate the children of "candidate" by expanding from the given cell.
// Returns the number of children that were marked "terminal".
int expandChildren(Candidate* candidate);
// Computes a set of initial candidates that cover the given region.
void getInitialCandidates();
GeoHashConverter* _hashConverter; // Not owned.
// min / max level as unsigned so as to be consistent with GeoHash
unsigned int _minLevel;
unsigned int _maxLevel;
int _maxCells;
// Save the copy of pointer temporarily to avoid passing this parameter internally.
// Only valid for the duration of a single getCovering() call.
R2Region const* _region;
// We keep the candidates that may intersect with this region in a priority queue.
typedef std::pair<int, Candidate*> QueueEntry;
// 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 CompareQueueEntries {
bool operator()(QueueEntry const& x, QueueEntry const& y) const {
return x.first < y.first;
}
};
typedef std::priority_queue<QueueEntry, std::vector<QueueEntry>, CompareQueueEntries>
CandidateQueue;
std::unique_ptr<CandidateQueue> _candidateQueue; // Priority queue owns candidate pointers.
std::unique_ptr<std::vector<GeoHash>> _results;
};
// An R2CellUnion is a region consisting of cells of various sizes.
class R2CellUnion {
MONGO_DISALLOW_COPYING(R2CellUnion);
public:
R2CellUnion() = default;
void init(const std::vector<GeoHash>& cellIds);
bool contains(const GeoHash cellId) const;
std::string toString() const;
private:
// Normalizes the cell union by discarding cells that are contained by other
// cells, replacing groups of 4 child cells by their parent cell whenever
// possible, and sorting all the cell ids in increasing order. Returns true
// if the number of cells was reduced.
bool normalize();
std::vector<GeoHash> _cellIds;
};
} /* namespace mongo */
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