Syntax

   @GeoHash(<command>, <attrName>) 
   
Arguments

   <command>   
   
      To specify whether to import or export the geometry of a feature from/to 
      an attribute.
   
      Range: (from_attribute|to_attribute)   
      
   <attrName>  
   
      The name of the attribute to have the geometry saved to or retrieved from 
      the feature.

      Range: String  
      
Description

   This command is used to either compute a geohash string from any given 
   geometry or to compute a rectangle geometry from any given geohash string. 

   Geohash is a geocode system that offers the possibility to gradually remove 
   characters from the end of the geocode in order to reduce its size, while 
   gradually losing precision. Because of the gradual loss of precision, 
   features that are nearby will usually share a similar prefix. Geohash can be 
   a good way to index point data in databases, because the similar prefix of 
   nearby features can make an easy proximity search. For more information on 
   geohashes, please refer to the Wikipedia article at 
   http://en.wikipedia.org/wiki/Geohash.

   Depending on the <command> string, the attribute given will be the source or 
   destination for the geometry of the feature. For to_attribute, the attribute 
   given will be the longest geohash that all the geometry of the feature can 
   use, for up to 12 characters. If the feature is either too large to generate 
   a geohash or if it is impossible to generate a single geohash to include all 
   the geometry, the attribute given will be the geohash of the point located in 
   the center of the feature's bounding box. For from_attribute, the geometry 
   will be replaced by a bounding box surrounding all the points that the 
   geohash given can represent.

      Note: In to_attribute mode, if the feature has no geometry, then no 
      attribute will be generated and a warning will be output. In 
      from_attribute mode, if the specified attribute has a blank value, then 
      the feature's geometry will be left untouched and a warning will be 
      output.