GeoHex for PL/pgSQL

# GeoHex for PL/pgSQL DESCRIPTION
GeoHex V3 for PL/pgSQL implemented by ASAHI Kosuke
http://twitter.com/waigania13

GeoHex.sql : ported from
    JavaScript implementation by @sa2da (http://geohex.net/hex_v3.01_core.js).

#REQUIRED
 PostgreSQL 9.0 or higher.
 PostGIS 1.5 or higher.
 
#INSTALL
 Loading GeoHex.sql and GeoHex-Extra.sql on your spatially-enabled database.
 
#USAGE
 select geohexGetZoneByLocation(35.0, 140.0, 7); -- (latitude, longitude, level)
 -> (11197,-4112,XM4848048,7,35.0023513065076,140)
 #(x,y,geohex code,level,latitude,longitude)
 
 select geohexGetZoneByCode('XM4848048'); -- (code, level)
 ->(11197,-4112,XM4848048,7,35.0023513065076,140)
 #(x,y,geohex code,level,latitude,longitude)
 
 select astext(geohexGetHexCoordsByZone(geohexGetZoneByCode('XM4848048'))); -- (zone (,srid=4326))
 ->POLYGON((139.9939033684 35.0023513065,139.9969516842 35.0066760579,140.0030483158 35.0066760579,140.0060966316 35.0023513065,140.0030483158 34.9980263265,139.9969516842 34.9980263265,139.9939033684 35.0023513065))
 
 select astext(geohexGetHexCoordsByZone(geohexGetZoneByCode('XM4848048'),900913)); -- (zone, srid)
 ->POLYGON((15584050.037133 4164200.68181666,15584389.3740957 4164788.43068025,15585068.0480209 4164788.43068025,15585407.3849836 4164200.68181666,15585068.0480209 4163612.93295387,15584389.3740957 4163612.93295387,15584050.037133 4164200.68181666))
 
 select * from geohexGetNeighborsByLocation(35.0, 140.0, 7, 1); -- (latitude, longitude, level, distance (,srid=4326))
 ->code, the_geom
 
 select * from geohexGetNeighborsByLocation(35.0, 140.0, 7, 1, 900913); -- (latitude, longitude, level, distance, srid)
 ->code, the_geom

 select * from geohexGetNeighborsByCode('XM4848044', 1); -- (code,distance (,srid=4326))
 ->code, the_geom

 select * from geohexGetNeighborsByCode('XM4848044', 1, 900913); -- (code, distance, srid)
 ->code, the_geom

 select * from geohexGetIntersectedGeohex(ST_GeomFromText('LINESTRING(140.0 35.0, 140.1 35.1)', 4326), 7); -- (geometry, level)
 ->code, the_geom
 
#LICENSE
This library "geohex-plpgsql" is a PL/pgSQL porting of "GeoHex"
 originally licensed by @sa2da (http://geogames.net)
 under Creative Commons BY-SA 2.1 Japan License.

geohex-plpgsql is licensed by ASAHI Kosuke
 under Creative Commons BY-SA 2.1 Japan License.

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
'Software'), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.