more description of over view

git-svn-id: http://svn.osgeo.org/postgis/trunk@8600 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/using_raster_dataman.xml b/doc/using_raster_dataman.xml
index faab0565cc4a5229193390740b1330058b526751..39bc424ad0ee96103147199d62010acbe656b838 100644 (file)
--- a/doc/using_raster_dataman.xml
+++ b/doc/using_raster_dataman.xml
@@ -490,7 +490,12 @@ Available GDAL raster formats:
                                        <para><varname>r_raster_column</varname> the raster column that this overview column services.</para>
                                </listitem>
                                <listitem>
-                                       <para><varname>overview_factor</varname> - this is the pyramid level of the overview table.  The higher the number the lower the resolution of the table.</para>
+                                       <para><varname>overview_factor</varname> - this is the pyramid level of the overview table.  The higher the number the lower the resolution of the table.
+                                       raster2pgsql if given a folder of images, will compute overview of each image file and load separately.  Level 1 is assumed and always the original file. Level 2 is
+                                       will have each tile represent 4 of the original.  So for example if you have a folder of 5000x5000 pixel image files that you chose to chunk 125x125, for each image file your base table will
+                                               have 5000/125 records = 40, your (l=2) <varname>o_2</varname> table will have ceiling(40/Power(2,2)) = 10 rows, your (l=3) <varname>o_3</varname> will have ceiling(40/Power(2,3) ) = 5 rows.
+                                               If your pixels aren't divisible by the size of your tiles, you'll get some scrap tiles (tiles not completely filled).  Note that each overview tile generated by raster2pgsql has the same number of
+                                               pixels as its parent, but is of a lower resolution where each pixel of it represents (Power(2,overview_factor) pixels of the original).</para>
                                </listitem>
                         </itemizedlist>