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provide an example of map algebra

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git-svn-id: http://svn.osgeo.org/postgis/trunk@6837 b70326c6-7e19-0410-871a-916f4a2858ee
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Regina Obe 2011-02-17 06:07:13 +00:00
parent 1578e46b40
commit e2b4788c69
1 changed files with 27 additions and 5 deletions
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32
doc/reference_raster.xml
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@ -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>