PostGIS
Description
Computes a GeoHash representation of a geometry. A GeoHash encodes a geographic Point into a text form that is sortable and searchable based on prefixing. A shorter GeoHash is a less precise representation of a point. It can be thought of as a box that contains the point.
Non-point geometry values with non-zero extent can also be mapped to GeoHash codes. The precision of the code depends on the geographic extent of the geometry.
If maxchars is not specified, the returned GeoHash code is for the
smallest cell containing the input geometry. Points return a GeoHash
with 20 characters of precision (about enough to hold the full double
precision of the input). Other geometric types may return a GeoHash with
less precision, depending on the extent of the geometry. Larger
geometries are represented with less precision, smaller ones with more
precision. The box determined by the GeoHash code always contains the
input feature.
If maxchars is specified the returned GeoHash code has at most that
many characters. It maps to a (possibly) lower precision representation
of the input geometry. For non-points, the starting point of the
calculation is the center of the bounding box of the geometry.
Availability: 1.4.0
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This
method supports Circular Strings and Curves.
Examples
SELECT ST_GeoHash( ST_Point(-126,48) );
st_geohash
----------------------
c0w3hf1s70w3hf1s70w3
SELECT ST_GeoHash( ST_Point(-126,48), 5);
st_geohash
------------
c0w3h
-- This line contains the point, so the GeoHash is a prefix of the point code
SELECT ST_GeoHash('LINESTRING(-126 48, -126.1 48.1)'::geometry);
st_geohash
------------
c0w3