12.16.10 Spatial Geohash Functions

Geohash is a system for encoding latitude and longitude coordinates of arbitrary precision into a text string. Geohash values are strings that contain only characters chosen from "0123456789bcdefghjkmnpqrstuvwxyz".

The functions in this section enable manipulation of geohash values, which provides applications the capabilities of importing and exporting geohash data, and of indexing and searching geohash values.

ST_GeoHash(longitude, latitude, max_length), ST_GeoHash(point, max_length)
Returns a geohash string in the connection character set and collation.
If any argument is NULL, the return value is NULL. If any argument is invalid, an error occurs.
For the first syntax, the longitude must be a number in the range [−180, 180], and the latitude must be a number in the range [−90, 90]. For the second syntax, a POINT value is required, where the X and Y coordinates are in the valid ranges for longitude and latitude, respectively.
The resulting string is no longer than max_length characters, which has an upper limit of 100. The string might be shorter than max_length characters because the algorithm that creates the geohash value continues until it has created a string that is either an exact representation of the location or max_length characters, whichever comes first.
```
mysql> SELECT ST_GeoHash(180,0,10), ST_GeoHash(-180,-90,15);
+----------------------+-------------------------+
| ST_GeoHash(180,0,10) | ST_GeoHash(-180,-90,15) |
+----------------------+-------------------------+
| xbpbpbpbpb           | 000000000000000         |
+----------------------+-------------------------+
```
ST_LatFromGeoHash(geohash_str)
Returns the latitude from a geohash string value, as a DOUBLE value in the range [−90, 90].
If the argument is NULL, the return value is NULL. If the argument is invalid, an error occurs.
The ST_LatFromGeoHash() decoding function reads no more than 433 characters from the geohash_str argument. That represents the upper limit on information in the internal representation of coordinate values. Characters past the 433rd are ignored, even if they are otherwise illegal and produce an error.
```
mysql> SELECT ST_LatFromGeoHash(ST_GeoHash(45,-20,10));
+------------------------------------------+
| ST_LatFromGeoHash(ST_GeoHash(45,-20,10)) |
+------------------------------------------+
|                                      -20 |
+------------------------------------------+
```
ST_LongFromGeoHash(geohash_str)
Returns the longitude from a geohash string value, as a DOUBLE value in the range [−180, 180].
If the argument is NULL, the return value is NULL. If the argument is invalid, an error occurs.
The remarks in the description of ST_LatFromGeoHash() regarding the maximum number of characters processed from the geohash_str argument also apply to ST_LongFromGeoHash().
```
mysql> SELECT ST_LongFromGeoHash(ST_GeoHash(45,-20,10));
+-------------------------------------------+
| ST_LongFromGeoHash(ST_GeoHash(45,-20,10)) |
+-------------------------------------------+
|                                        45 |
+-------------------------------------------+
```
ST_PointFromGeoHash(geohash_str, srid)
Returns a POINT value containing the decoded geohash value, given a geohash string value.
The X and Y coordinates of the point are the longitude in the range [−180, 180] and the latitude in the range [−90, 90], respectively.
If any argument is NULL, the return value is NULL. If any argument is invalid, an error occurs.
The srid argument is an unsigned 32-bit integer.
The remarks in the description of ST_LatFromGeoHash() regarding the maximum number of characters processed from the geohash_str argument also apply to ST_PointFromGeoHash().
```
mysql> SET @gh = ST_GeoHash(45,-20,10);
mysql> SELECT ST_AsText(ST_PointFromGeoHash(@gh,0));
+---------------------------------------+
| ST_AsText(ST_PointFromGeoHash(@gh,0)) |
+---------------------------------------+
| POINT(45 -20)                         |
+---------------------------------------+
```