rocksdb/utilities/geodb/geodb_impl.cc

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
#include "utilities/geodb/geodb_impl.h"
#define __STDC_FORMAT_MACROS
#include <vector>
#include <map>
#include <string>
#include <limits>
#include "db/filename.h"
#include "util/coding.h"
//
// There are two types of keys. The first type of key-values
// maps a geo location to the set of object ids and their values.
// Table 1
// key : p + : + $quadkey + : + $id +
// : + $latitude + : + $longitude
// value : value of the object
// This table can be used to find all objects that reside near
// a specified geolocation.
//
// Table 2
// key : 'k' + : + $id
// value: $quadkey
namespace rocksdb {
GeoDBImpl::GeoDBImpl(DB* db, const GeoDBOptions& options) :
GeoDB(db, options), db_(db), options_(options) {
}
GeoDBImpl::~GeoDBImpl() {
}
Status GeoDBImpl::Insert(const GeoObject& obj) {
WriteBatch batch;
// It is possible that this id is already associated with
// with a different position. We first have to remove that
// association before we can insert the new one.
// remove existing object, if it exists
GeoObject old;
Status status = GetById(obj.id, &old);
if (status.ok()) {
assert(obj.id.compare(old.id) == 0);
std::string quadkey = PositionToQuad(old.position, Detail);
std::string key1 = MakeKey1(old.position, old.id, quadkey);
std::string key2 = MakeKey2(old.id);
batch.Delete(Slice(key1));
batch.Delete(Slice(key2));
} else if (status.IsNotFound()) {
// What if another thread is trying to insert the same ID concurrently?
} else {
return status;
}
// insert new object
std::string quadkey = PositionToQuad(obj.position, Detail);
std::string key1 = MakeKey1(obj.position, obj.id, quadkey);
std::string key2 = MakeKey2(obj.id);
batch.Put(Slice(key1), Slice(obj.value));
batch.Put(Slice(key2), Slice(quadkey));
return db_->Write(woptions_, &batch);
}
Status GeoDBImpl::GetByPosition(const GeoPosition& pos,
const Slice& id,
std::string* value) {
std::string quadkey = PositionToQuad(pos, Detail);
std::string key1 = MakeKey1(pos, id, quadkey);
return db_->Get(roptions_, Slice(key1), value);
}
Status GeoDBImpl::GetById(const Slice& id, GeoObject* object) {
Status status;
Slice quadkey;
// create an iterator so that we can get a consistent picture
// of the database.
Iterator* iter = db_->NewIterator(roptions_);
// create key for table2
std::string kt = MakeKey2(id);
Slice key2(kt);
iter->Seek(key2);
if (iter->Valid() && iter->status().ok()) {
if (iter->key().compare(key2) == 0) {
quadkey = iter->value();
}
}
if (quadkey.size() == 0) {
delete iter;
return Status::NotFound(key2);
}
//
// Seek to the quadkey + id prefix
//
std::string prefix = MakeKey1Prefix(quadkey.ToString(), id);
iter->Seek(Slice(prefix));
assert(iter->Valid());
if (!iter->Valid() || !iter->status().ok()) {
delete iter;
return Status::NotFound();
}
// split the key into p + quadkey + id + lat + lon
std::vector<std::string> parts;
Slice key = iter->key();
StringSplit(&parts, key.ToString(), ':');
assert(parts.size() == 5);
assert(parts[0] == "p");
assert(parts[1] == quadkey);
assert(parts[2] == id);
// fill up output parameters
object->position.latitude = atof(parts[3].c_str());
object->position.longitude = atof(parts[4].c_str());
object->id = id.ToString(); // this is redundant
object->value = iter->value().ToString();
delete iter;
return Status::OK();
}
Status GeoDBImpl::Remove(const Slice& id) {
// Read the object from the database
GeoObject obj;
Status status = GetById(id, &obj);
if (!status.ok()) {
return status;
}
// remove the object by atomically deleting it from both tables
std::string quadkey = PositionToQuad(obj.position, Detail);
std::string key1 = MakeKey1(obj.position, obj.id, quadkey);
std::string key2 = MakeKey2(obj.id);
WriteBatch batch;
batch.Delete(Slice(key1));
batch.Delete(Slice(key2));
return db_->Write(woptions_, &batch);
}
Status GeoDBImpl::SearchRadial(const GeoPosition& pos,
double radius,
std::vector<GeoObject>* values,
int number_of_values) {
// Gather all bounding quadkeys
std::vector<std::string> qids;
Status s = searchQuadIds(pos, radius, &qids);
if (!s.ok()) {
return s;
}
// create an iterator
Iterator* iter = db_->NewIterator(ReadOptions());
// Process each prospective quadkey
for (std::string qid : qids) {
// The user is interested in only these many objects.
if (number_of_values == 0) {
break;
}
// convert quadkey to db key prefix
std::string dbkey = MakeQuadKeyPrefix(qid);
for (iter->Seek(dbkey);
number_of_values > 0 && iter->Valid() && iter->status().ok();
iter->Next()) {
// split the key into p + quadkey + id + lat + lon
std::vector<std::string> parts;
Slice key = iter->key();
StringSplit(&parts, key.ToString(), ':');
assert(parts.size() == 5);
assert(parts[0] == "p");
std::string* quadkey = &parts[1];
// If the key we are looking for is a prefix of the key
// we found from the database, then this is one of the keys
// we are looking for.
auto res = std::mismatch(qid.begin(), qid.end(), quadkey->begin());
if (res.first == qid.end()) {
GeoPosition pos(atof(parts[3].c_str()), atof(parts[4].c_str()));
GeoObject obj(pos, parts[4], iter->value().ToString());
values->push_back(obj);
number_of_values--;
} else {
break;
}
}
}
delete iter;
return Status::OK();
}
std::string GeoDBImpl::MakeKey1(const GeoPosition& pos, Slice id,
std::string quadkey) {
std::string lat = std::to_string(pos.latitude);
std::string lon = std::to_string(pos.longitude);
std::string key = "p:";
key.reserve(5 + quadkey.size() + id.size() + lat.size() + lon.size());
key.append(quadkey);
key.append(":");
key.append(id.ToString());
key.append(":");
key.append(lat);
key.append(":");
key.append(lon);
return key;
}
std::string GeoDBImpl::MakeKey2(Slice id) {
std::string key = "k:";
key.append(id.ToString());
return key;
}
std::string GeoDBImpl::MakeKey1Prefix(std::string quadkey,
Slice id) {
std::string key = "p:";
key.reserve(3 + quadkey.size() + id.size());
key.append(quadkey);
key.append(":");
key.append(id.ToString());
return key;
}
std::string GeoDBImpl::MakeQuadKeyPrefix(std::string quadkey) {
std::string key = "p:";
key.append(quadkey);
return key;
}
void GeoDBImpl::StringSplit(std::vector<std::string>* tokens,
const std::string &text, char sep) {
std::size_t start = 0, end = 0;
while ((end = text.find(sep, start)) != std::string::npos) {
tokens->push_back(text.substr(start, end - start));
start = end + 1;
}
tokens->push_back(text.substr(start));
}
// convert degrees to radians
double GeoDBImpl::radians(double x) {
return (x * PI) / 180;
}
// convert radians to degrees
double GeoDBImpl::degrees(double x) {
return (x * 180) / PI;
}
// convert a gps location to quad coordinate
std::string GeoDBImpl::PositionToQuad(const GeoPosition& pos,
int levelOfDetail) {
Pixel p = PositionToPixel(pos, levelOfDetail);
Tile tile = PixelToTile(p);
return TileToQuadKey(tile, levelOfDetail);
}
GeoPosition GeoDBImpl::displaceLatLon(double lat, double lon,
double deltay, double deltax) {
double dLat = deltay / EarthRadius;
double dLon = deltax / (EarthRadius * cos(radians(lat)));
return GeoPosition(lat + degrees(dLat),
lon + degrees(dLon));
}
//
// Return the distance between two positions on the earth
//
double GeoDBImpl::distance(double lat1, double lon1,
double lat2, double lon2) {
double lon = radians(lon2 - lon1);
double lat = radians(lat2 - lat1);
double a = (sin(lat / 2) * sin(lat / 2)) +
cos(radians(lat1)) * cos(radians(lat2)) *
(sin(lon / 2) * sin(lon / 2));
double angle = 2 * atan2(sqrt(a), sqrt(1 - a));
return angle * EarthRadius;
}
//
// Returns all the quadkeys inside the search range
//
Status GeoDBImpl::searchQuadIds(const GeoPosition& position,
double radius,
std::vector<std::string>* quadKeys) {
// get the outline of the search square
GeoPosition topLeftPos = boundingTopLeft(position, radius);
GeoPosition bottomRightPos = boundingBottomRight(position, radius);
Pixel topLeft = PositionToPixel(topLeftPos, Detail);
Pixel bottomRight = PositionToPixel(bottomRightPos, Detail);
// how many level of details to look for
int numberOfTilesAtMaxDepth = floor((bottomRight.x - topLeft.x) / 256);
int zoomLevelsToRise = floor(log(numberOfTilesAtMaxDepth) / log(2));
zoomLevelsToRise++;
int levels = std::max(0, Detail - zoomLevelsToRise);
quadKeys->push_back(PositionToQuad(GeoPosition(topLeftPos.latitude,
topLeftPos.longitude),
levels));
quadKeys->push_back(PositionToQuad(GeoPosition(topLeftPos.latitude,
bottomRightPos.longitude),
levels));
quadKeys->push_back(PositionToQuad(GeoPosition(bottomRightPos.latitude,
topLeftPos.longitude),
levels));
quadKeys->push_back(PositionToQuad(GeoPosition(bottomRightPos.latitude,
bottomRightPos.longitude),
levels));
return Status::OK();
}
// Determines the ground resolution (in meters per pixel) at a specified
// latitude and level of detail.
// Latitude (in degrees) at which to measure the ground resolution.
// Level of detail, from 1 (lowest detail) to 23 (highest detail).
// Returns the ground resolution, in meters per pixel.
double GeoDBImpl::GroundResolution(double latitude, int levelOfDetail) {
latitude = clip(latitude, MinLatitude, MaxLatitude);
return cos(latitude * PI / 180) * 2 * PI * EarthRadius /
MapSize(levelOfDetail);
}
// Converts a point from latitude/longitude WGS-84 coordinates (in degrees)
// into pixel XY coordinates at a specified level of detail.
GeoDBImpl::Pixel GeoDBImpl::PositionToPixel(const GeoPosition& pos,
int levelOfDetail) {
double latitude = clip(pos.latitude, MinLatitude, MaxLatitude);
double x = (pos.longitude + 180) / 360;
double sinLatitude = sin(latitude * PI / 180);
double y = 0.5 - log((1 + sinLatitude) / (1 - sinLatitude)) / (4 * PI);
double mapSize = MapSize(levelOfDetail);
double X = floor(clip(x * mapSize + 0.5, 0, mapSize - 1));
double Y = floor(clip(y * mapSize + 0.5, 0, mapSize - 1));
return Pixel((unsigned int)X, (unsigned int)Y);
}
GeoPosition GeoDBImpl::PixelToPosition(const Pixel& pixel, int levelOfDetail) {
double mapSize = MapSize(levelOfDetail);
double x = (clip(pixel.x, 0, mapSize - 1) / mapSize) - 0.5;
double y = 0.5 - (clip(pixel.y, 0, mapSize - 1) / mapSize);
double latitude = 90 - 360 * atan(exp(-y * 2 * PI)) / PI;
double longitude = 360 * x;
return GeoPosition(latitude, longitude);
}
// Converts a Pixel to a Tile
GeoDBImpl::Tile GeoDBImpl::PixelToTile(const Pixel& pixel) {
unsigned int tileX = floor(pixel.x / 256);
unsigned int tileY = floor(pixel.y / 256);
return Tile(tileX, tileY);
}
GeoDBImpl::Pixel GeoDBImpl::TileToPixel(const Tile& tile) {
unsigned int pixelX = tile.x * 256;
unsigned int pixelY = tile.y * 256;
return Pixel(pixelX, pixelY);
}
// Convert a Tile to a quadkey
std::string GeoDBImpl::TileToQuadKey(const Tile& tile, int levelOfDetail) {
std::stringstream quadKey;
for (int i = levelOfDetail; i > 0; i--) {
char digit = '0';
int mask = 1 << (i - 1);
if ((tile.x & mask) != 0) {
digit++;
}
if ((tile.y & mask) != 0) {
digit++;
digit++;
}
quadKey << digit;
}
return quadKey.str();
}
//
// Convert a quadkey to a tile and its level of detail
//
void GeoDBImpl::QuadKeyToTile(std::string quadkey, Tile* tile,
int *levelOfDetail) {
tile->x = tile->y = 0;
*levelOfDetail = quadkey.size();
const char* key = reinterpret_cast<const char *>(quadkey.c_str());
for (int i = *levelOfDetail; i > 0; i--) {
int mask = 1 << (i - 1);
switch (key[*levelOfDetail - i]) {
case '0':
break;
case '1':
tile->x |= mask;
break;
case '2':
tile->y |= mask;
break;
case '3':
tile->x |= mask;
tile->y |= mask;
break;
default:
std::stringstream msg;
msg << quadkey;
msg << " Invalid QuadKey.";
throw std::runtime_error(msg.str());
}
}
}
} // namespace rocksdb