postgis/extras/wkb_reader

This is a very simple example of using binary cursors to move binary data from 
the server to the client.

We convert the GEOMETRY to the OpenGIS Well Known Binary (WKB) format before 
sending it to the client.

The WKB format contains information about the endian of the data, so it can be
used for transfer between servers and clients that are not the same endian 
(ie. between i386 and sparc)

See http://www.opengis.org/techno/specs/99-049.rtf page 3-24 for the WKB 
specification.

Z and M coordinates presence is encoded by or'ing WKBZOFFSET (0x80000000)
and WKBMOFFSET (0x40000000) to the type.
Points can then be 24 bytes (XYZ,XYM) or 32 bytes (XYZM)

You can force geometries to be returned as 2d using the force_2d()
function. For example:

  select asBinary(force_2d(geom)) from mytable;

If the client is running on a i386, you should use asBinary(geom, 'NDR')
and on a sparc you should use asBinary(geom, 'XDR') so you do not causes
an endian shift on both the server and client.