void geohash(double longitude, double latitude, char* hash) {
if ((fabs(longitude) > 180.0) || (fabs(latitude) > 90.0)) {
strcpy(hash, "error");
return;
}
GeoHashRange r[2];
GeoHashBits h;
geohashEncodeWGS84(longitude, latitude, GEO_STEP_MAX, &h);
r[0].min = -180;
r[0].max = 180;
r[1].min = -90;
r[1].max = 90;
geohashEncode(&r[0], &r[1], longitude, latitude, 26, &h);
for (int i = 0; i < 11; i++) {
int idx = (h.bits >> (52-((i+1)*5))) & 0x1f;
hash[i] = geoalphabet[idx];
}
hash[11] = '\0';
}
GeoHashRadius geohashGetAreasByRadius(uint8_t coord_type, double latitude,
double longitude, double radius_meters) {
GeoHashRange lat_range, long_range;
GeoHashRadius radius = { { 0 } };
GeoHashBits hash = { 0 };
GeoHashNeighbors neighbors = { { 0 } };
GeoHashArea area = { { 0 } };
double delta_longitude, delta_latitude;
double min_lat, max_lat, min_lon, max_lon;
int steps;
if (coord_type == GEO_WGS84_TYPE) {
double bounds[4];
geohashBoundingBox(latitude, longitude, radius_meters, bounds);
min_lat = bounds[0];
min_lon = bounds[1];
max_lat = bounds[2];
max_lon = bounds[3];
} else {
delta_latitude = delta_longitude = radius_meters;
min_lat = latitude - delta_latitude;
max_lat = latitude + delta_latitude;
min_lon = longitude - delta_longitude;
max_lon = longitude + delta_longitude;
}
steps = geohashEstimateStepsByRadius(radius_meters);
geohashGetCoordRange(coord_type, &lat_range, &long_range);
geohashEncode(lat_range, long_range, latitude, longitude, steps, &hash);
geohashNeighbors(&hash, &neighbors);
geohashDecode(lat_range, long_range, hash, &area);
if (area.latitude.min < min_lat) {
GZERO(neighbors.south);
GZERO(neighbors.south_west);
GZERO(neighbors.south_east);
}
if (area.latitude.max > max_lat) {
GZERO(neighbors.north);
GZERO(neighbors.north_east);
GZERO(neighbors.north_west);
}
if (area.longitude.min < min_lon) {
GZERO(neighbors.west);
GZERO(neighbors.south_west);
GZERO(neighbors.north_west);
}
if (area.longitude.max > max_lon) {
GZERO(neighbors.east);
GZERO(neighbors.south_east);
GZERO(neighbors.north_east);
}
radius.hash = hash;
radius.neighbors = neighbors;
radius.area = area;
return radius;
}
/* Return a set of areas (center + 8) that are able to cover a range query
* for the specified position and radius. */
GeoHashRadius geohashGetAreasByRadius(double longitude, double latitude, double radius_meters) {
GeoHashRange long_range, lat_range;
GeoHashRadius radius;
GeoHashBits hash;
GeoHashNeighbors neighbors;
GeoHashArea area;
double min_lon, max_lon, min_lat, max_lat;
double bounds[4];
int steps;
geohashBoundingBox(longitude, latitude, radius_meters, bounds);
min_lon = bounds[0];
min_lat = bounds[1];
max_lon = bounds[2];
max_lat = bounds[3];
steps = geohashEstimateStepsByRadius(radius_meters,latitude);
geohashGetCoordRange(&long_range,&lat_range);
geohashEncode(&long_range,&lat_range,longitude,latitude,steps,&hash);
geohashNeighbors(&hash,&neighbors);
geohashDecode(long_range,lat_range,hash,&area);
/* Check if the step is enough at the limits of the covered area.
* Sometimes when the search area is near an edge of the
* area, the estimated step is not small enough, since one of the
* north / south / west / east square is too near to the search area
* to cover everything. */
int decrease_step = 0;
{
GeoHashArea north, south, east, west;
geohashDecode(long_range, lat_range, neighbors.north, &north);
geohashDecode(long_range, lat_range, neighbors.south, &south);
geohashDecode(long_range, lat_range, neighbors.east, &east);
geohashDecode(long_range, lat_range, neighbors.west, &west);
if (geohashGetDistance(longitude,latitude,longitude,north.latitude.max)
< radius_meters) decrease_step = 1;
if (geohashGetDistance(longitude,latitude,longitude,south.latitude.min)
< radius_meters) decrease_step = 1;
if (geohashGetDistance(longitude,latitude,east.longitude.max,latitude)
< radius_meters) decrease_step = 1;
if (geohashGetDistance(longitude,latitude,west.longitude.min,latitude)
< radius_meters) decrease_step = 1;
}
if (decrease_step) {
steps--;
geohashEncode(&long_range,&lat_range,longitude,latitude,steps,&hash);
geohashNeighbors(&hash,&neighbors);
geohashDecode(long_range,lat_range,hash,&area);
}
/* Exclude the search areas that are useless. */
if (area.latitude.min < min_lat) {
GZERO(neighbors.south);
GZERO(neighbors.south_west);
GZERO(neighbors.south_east);
}
if (area.latitude.max > max_lat) {
GZERO(neighbors.north);
GZERO(neighbors.north_east);
GZERO(neighbors.north_west);
}
if (area.longitude.min < min_lon) {
GZERO(neighbors.west);
GZERO(neighbors.south_west);
GZERO(neighbors.north_west);
}
if (area.longitude.max > max_lon) {
GZERO(neighbors.east);
GZERO(neighbors.south_east);
GZERO(neighbors.north_east);
}
radius.hash = hash;
radius.neighbors = neighbors;
radius.area = area;
return radius;
}