Start raster_overviews section

git-svn-id: http://svn.osgeo.org/postgis/trunk@8424 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/using_raster_dataman.xml b/doc/using_raster_dataman.xml
index 95c2846f9146098f57eab500f46fec871652bbe0..7c51ee4157c4bce7c97697ca3c45f168620a5bca 100644 (file)
--- a/doc/using_raster_dataman.xml
+++ b/doc/using_raster_dataman.xml
@@ -235,6 +235,7 @@ psql -d gisdb -f elev.sql</programlisting>
           </listitem>
         </orderedlist>
         <sect2 id="RT_Raster_Columns">
+               <title>Raster Columns Catalog</title>
                <para>The <varname>raster_columns</varname> is a catalog of all columns in the table taht are of type raster.  It is a view utilizing the constraints on the tables
                so the information is always consistent even if you restore one raster table from a backup of another database.  The following columns exist in the <varname>raster_columns</varname> catalog.</para>
                <para>If you created your tables not with the loader or forgot to specified the <varname>-C</varname> flag during load, you can enforce the constraints after the 
@@ -288,5 +289,14 @@ psql -d gisdb -f elev.sql</programlisting>
                                </listitem>
                        </orderedlist>
         </sect2>
+        <sect2 id="RT_Raster_Overviews">
+               <title>Raster Overviews</title>
+               <para><varname>raster_overviews</varname> catalogs information about raster table columns used for overviews and additional information about them that is useful to know when utilizing overviews. Overview tables are cataloged in both <varname>raster_columns</varname> and <varname>raster_overviews</varname> because they are rasters in their own right but also serve an additional special purpose. These are generated along-side the main raster table when you use the <varname>-l</varname> switch in raster loading.</para>
+               <para>Two main reasons for overviews are:</para>
+               <orderedlist>
+                       <listitem>Low resolution representation of the core tables common used for fast mapping zoom-out.</listitem>
+                       <listitem>Computations are faster to do on them though the computations are not as accurate as the high-res tables, they can be suitable in many rule-of-thumb computations.</listitem>
+               </orderedlist>
+        </sect2>
    </sect1>
 </chapter>