= PostGIS FAQ =

Frequently Asked Questions about PostGIS extension.

[[TOC(depth=2, noheading, inline)]]

== PostgreSQL Can't install under Windows Vista ==
Refer to these instructions [UsersWikiWinVista Issues with installing under Windows Vista]

== How to create geometry from hex-encoded Well-Known-Binary string using SQL? ==

This is two-steps operation which can be executed in single [http://www.postgresql.org/docs/8.3/static/sql-commands.html SQL] statement. The steps include:
 * Convert [http://postgis.refractions.net/documentation/manual-svn/ch04.html Well-Known-Binary] data in hexadecimal string form to raw binary using PostgreSQL function [http://www.postgresql.org/docs/8.3/static/functions-binarystring.html decode].
 * Construct geometry object from WKB in raw binary form.

Example:

{{{
#!sql
=# SELECT ST_AsText(ST_GeomFromWKB(decode('0101000000e5d022dbf93e2e40dbf97e6abc743540', 'hex'), -1));
      st_astext       
----------------------
 POINT(15.123 21.456)
}}}

== How to write geometry Well-Known-Binary to hex-encoded string? ==

First, query for geometry object in [http://postgis.refractions.net/documentation/manual-svn/ch04.html Well-Known-Binary] format using [http://postgis.refractions.net/documentation/manual-svn/ST_AsBinary.html ST_AsBinary] function. Then, [http://www.postgresql.org/docs/8.3/static/functions-binarystring.html encode] raw WKB to hex string.

Examples:

 * selecting geometry from table:

{{{
#!sql
# SELECT encode(ST_AsBinary(the_geom), 'hex');
                   encode                   
--------------------------------------------
 0101000000e5d022dbf93e2e40dbf97e6abc743540
}}}

 * constructing geometry in-place from given Well-Known-Text:

{{{
#!sql
# SELECT encode(ST_AsBinary(ST_GeomFromText('POINT(15.123 21.456)', -1)), 'hex');
                   encode                   
--------------------------------------------
 0101000000e5d022dbf93e2e40dbf97e6abc743540
}}}