#3116: SFCGAL add documentation for geometry backend switch. Patch from Vincent Mora

git-svn-id: http://svn.osgeo.org/postgis/trunk@13777 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/reference_sfcgal.xml b/doc/reference_sfcgal.xml
index d19144b5e1a05d14ae462c92e5df9a9807a4a1c3..952e8875c18195f96dfb5c64da09b4a36ba72f1c 100644 (file)
--- a/doc/reference_sfcgal.xml
+++ b/doc/reference_sfcgal.xml
@@ -9,6 +9,13 @@
         <para> 
             Installation instructions of the library can be found on SFCGAL home page <ulink url="http://www.sfcgal.org">http://www.sfcgal.org</ulink>. 
             To load the functions create extension postgis_sfcgal. 
+        </para>
+        <para>
+          Some SFCGAL functions replace standard ones (ST_Intersects, ST_Intersection, ST_Difference, ST_Union, ST_Area and ST_Distance), to switch between standard functions and SFCGAL function use:
+       <programlisting>SET postgis.backend = sfcgal;</programlisting>
+       and
+       <programlisting>SET postgis.backend = geos;</programlisting>
+        
         </para>
                </abstract>
        </sect1info>