From: Regina Obe <lr@pcorp.us>
Date: Thu, 15 Dec 2011 01:54:12 +0000 (+0000)
Subject: Start raster_overviews section
X-Git-Tag: 2.0.0alpha1~449
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=ae47ce85637f55d14a9259d69fc1e73f808487b2;p=postgis

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 95c2846f9..7c51ee415 100644
--- 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>