From: Regina Obe <lr@pcorp.us>
Date: Thu, 17 Feb 2011 06:07:13 +0000 (+0000)
Subject: provide an example of map algebra
X-Git-Tag: 2.0.0alpha1~1963
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e2b4788c69ec6fb4ad0e73a706c8f5ed516f9c52;p=postgis

provide an example of map algebra

git-svn-id: http://svn.osgeo.org/postgis/trunk@6837 b70326c6-7e19-0410-871a-916f4a2858ee
---

diff --git a/doc/reference_raster.xml b/doc/reference_raster.xml
index 6eeb357c0..773af7448 100644
--- a/doc/reference_raster.xml
+++ b/doc/reference_raster.xml
@@ -3295,7 +3295,7 @@ WHERE A.rid =2 ) As foo;
 		<refentry id="RT_ST_MapAlgebra">
 			<refnamediv>
 				<refname>ST_MapAlgebra</refname>
-				<refpurpose>Creates a new raster formed by applying algebraic operations defined by the expression on the input raster and of pixeeltype provided.  band 1 is assumed if no band is specified.</refpurpose>
+				<refpurpose>Creates a new one band raster formed by applying a valid PostgreSQL algebraic operations on the input raster band and of pixeeltype provided.  band 1 is assumed if no band is specified.</refpurpose>
 			</refnamediv>
 		
 			<refsynopsisdiv>
@@ -3345,8 +3345,11 @@ WHERE A.rid =2 ) As foo;
 			<refsection>
 				<title>Description</title>
 				
-				<para>Creates a new raster formed by applying algebraic operations defined by the expression on the input raster. If no band number is specified
-        band 1 is assumed.</para>
+				<para>Creates a new one band raster formed by applying algebraic operations defined by the <varname>expression</varname> on the input raster (<varname>rast</varname>). If no <varnum>band</varnum> is specified
+        band 1 is assumed.  The new raster will have the same georeference, width, and height as the original raster but will only have one band.</para>
+        
+                 <para>If <varname>pixeltype</varname> is passed in, then the new raster will have a band of that pixeltype.  If no pixeltype is passed in, then the new raster band will have the same pixeltype as the input <varname>rast</varname></para>
+                 <para>Use the term <varname>rast</varname> to refer to the band you are changing.</para>
 			
                  <para>Availability: 2.0.0 </para>
              </refsection>
@@ -3354,12 +3357,31 @@ WHERE A.rid =2 ) As foo;
              <refsection>
 				<title>Examples</title>
 				
-				<!-- TODO -->
+				<para>Create a new 1 band raster from our original that is  a function of modulo 2 of the original raster band.</para>
+				<programlisting>ALTER TABLE dummy_rast ADD COLUMN map_rast raster;
+UPDATE dummy_rast SET map_rast = ST_MapAlgebra(rast,'mod(rast,2)') WHERE rid = 2;
+
+SELECT ST_Value(rast,1,i,j) As origval, ST_Value(map_rast, 1, i, j) As mapval
+FROM dummy_rast CROSS JOIN generate_series(1, 3) AS i CROSS JOIN generate_series(1,3) AS j
+WHERE rid = 2;
+
+ origval | mapval
+---------+--------
+     253 |      1
+     254 |      0
+     253 |      1
+     253 |      1
+     254 |      0
+     254 |      0
+     250 |      0
+     254 |      0
+     254 |      0
+				</programlisting>				
 			</refsection>
 
 			<refsection>
 				<title>See Also</title>
-				<para></para>
+				<para><xref linkend="RT_ST_GeoReference" />, <xref linkend="RT_ST_BandPixelType" /></para>
 			</refsection>
 		</refentry>