Example of how to use only psql to output a raster image.

git-svn-id: http://svn.osgeo.org/postgis/trunk@9192 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/using_raster_dataman.xml b/doc/using_raster_dataman.xml
index 9b946020c151d5e91378963c0e4270a36fbbcb66..c6e6db5f913cdf0e54d169a55f4bb8b8b895189d 100644 (file)
--- a/doc/using_raster_dataman.xml
+++ b/doc/using_raster_dataman.xml
@@ -718,5 +718,29 @@ $$ LANGUAGE plpythonu;]]></programlisting>
  C:/temp/slices5.png    
 </programlisting>
                </sect2>
+               <sect2 id="RasterOutput_PSQL">
+                       <title>Outputting Rasters with PSQL</title>
+                       <para>Sadly PSQL doesn't have easy to use built-in functionality for outputting binaries.  This is a bit of a hack and based on one of the suggestions outlined in
+                               <ulink url="http://people.planetpostgresql.org/andrew/index.php?/archives/196-Clever-trick-challenge.html">Clever Trick Challenge -- Outputting bytea with psql</ulink> that piggy backs on PostgreSQL somewhat legacy large object support.  To use first launch your psql commandline connected to your database.
+                       </para>
+                       <para>Unlike the python approach, this approach creates the file on your local computer.</para>
+                       <screen>SELECT oid, lowrite(lo_open(oid, 131072), png) As num_bytes
+ FROM 
+ ( VALUES (lo_create(0), 
+   ST_AsPNG( (SELECT rast FROM aerials.boston WHERE rid=1) ) 
+  ) ) As v(oid,png);
+-- you'll get an output something like --
+   oid   | num_bytes
+---------+-----------
+ 2630819 |     74860
+ 
+-- next note the oid and do this replacing the c:/test.png to file path location
+-- on your local computer
+ \lo_export 2630819 'C:/temp/aerial_samp.png'
+ 
+-- this deletes the file from large object storage on db
+SELECT lo_unlink(2630819);
+                       </screen>
+               </sect2>
    </sect1>
 </chapter>