<refsection>
<title>See Also</title>
- <para><xref linkend="RT_ST_BandPixelType" />, <xref linkend="RT_ST_GeoReference" />, <xref linkend="RT_ST_Value" /></para>
+ <para><xref linkend="RT_ST_MapAlgebraFct" />, <xref linkend="RT_ST_BandPixelType" />, <xref linkend="RT_ST_GeoReference" />, <xref linkend="RT_ST_Value" /></para>
+ </refsection>
+ </refentry>
+
+ <refentry id="RT_ST_MapAlgebraFct">
+ <refnamediv>
+ <refname>ST_MapAlgebraFct</refname>
+ <refpurpose>Creates a new one band raster formed by applying a valid PostgreSQL function on the input raster band and of pixeltype prodived. Band 1 is assumed if no band is specified.</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>raster <function>ST_MapAlgebraFct</function></funcdef>
+ <paramdef><type>raster</type> <parameter>rast</parameter></paramdef>
+ <paramdef><type>integer</type> <parameter>band</parameter></paramdef>
+ <paramdef><type>text</type> <parameter>pixeltype</parameter></paramdef>
+ <paramdef><type>regprocedure</type> <parameter>userfunction</parameter></paramdef>
+ <paramdef choice='opt'><type>text[]</type> <parameter>VARIADIC args</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>raster <function>ST_MapAlgebraFct</function></funcdef>
+ <paramdef><type>raster</type> <parameter>rast</parameter></paramdef>
+ <paramdef><type>integer</type> <parameter>band</parameter></paramdef>
+ <paramdef><type>regprocedure</type> <parameter>userfunction</parameter></paramdef>
+ <paramdef choice='opt'><type>text[]</type> <parameter>VARIADIC args</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>raster <function>ST_MapAlgebraFct</function></funcdef>
+ <paramdef><type>raster</type> <parameter>rast</parameter></paramdef>
+ <paramdef><type>text</type> <parameter>pixeltype</parameter></paramdef>
+ <paramdef><type>regprocedure</type> <parameter>userfunction</parameter></paramdef>
+ <paramdef choice='opt'><type>text[]</type> <parameter>VARIADIC args</parameter></paramdef>
+ </funcprototype>
+
+ <funcprototype>
+ <funcdef>raster <function>ST_MapAlgebraFct</function></funcdef>
+ <paramdef><type>raster</type> <parameter>rast</parameter></paramdef>
+ <paramdef><type>regprocedure</type> <parameter>userfunction</parameter></paramdef>
+ <paramdef choice='opt'><type>text[]</type> <parameter>VARIADIC args</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsection>
+ <title>Description</title>
+
+ <para>Creates a new one band raster formed by applying a valid PostgreSQL function specified by the <varname>userfunction</varname> on the input raster (<varname>rast</varname>). If no <varname>band</varname> 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 pixeltype is passed NULL, then the new raster band will have the same pixeltype as the input <varname>rast</varname> band.</para>
+
+ <para>Availability: 2.0.0</para>
+ </refsection>
+
+ <refsection>
+ <title>Examples</title>
+
+ <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;
+CREATE FUNCTION mod_fct(pixel float, variadic args text[])
+RETURNS float
+AS $$
+BEGIN
+ RETURN pixel::integer % 2;
+END;
+$$
+LANGUAGE 'plpgsql';
+
+UPDATE dummy_rast SET map_rast = ST_MapAlgebraFct(rast,NULL,'mod_fct(float,text[])'::regprocedure) 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>
+ <para>Create a new 1 band raster of pixel-type 2BUI from our original that is reclassified and set the nodata value to a passed parameter to the user function (0).</para>
+ <programlisting>ALTER TABLE dummy_rast ADD COLUMN map_rast2 raster;
+CREATE FUNCTION classify_fct(pixel float, variadic args text[])
+RETURNS float
+AS
+$$
+DECLARE
+ nodata float := 0;
+BEGIN
+ IF NOT args[1] IS NULL THEN
+ nodata := args[1];
+ END IF;
+ IF pixel < 251 THEN
+ RETURN 1;
+ ELSIF pixel = 252 THEN
+ RETURN 2;
+ ELSIF pixel > 252 THEN
+ RETURN 3;
+ ELSE
+ RETURN nodata;
+ END IF;
+END;
+$$
+LANGUAGE 'plpgsql';
+UPDATE dummy_rast SET map_rast2 = ST_MapAlgebraFct(rast,'2BUI','classify_fct(float,text[])'::regprocedure, '0') WHERE rid = 2;
+
+SELECT DISTINCT ST_Value(rast,1,i,j) As origval, ST_Value(map_rast2, 1, i, j) As mapval
+FROM dummy_rast CROSS JOIN generate_series(1, 5) AS i CROSS JOIN generate_series(1,5) AS j
+WHERE rid = 2;
+
+ origval | mapval
+---------+--------
+ 249 | 1
+ 250 | 1
+ 251 |
+ 252 | 2
+ 253 | 3
+ 254 | 3
+
+SELECT ST_BandPixelType(map_rast2) As b1pixtyp
+FROM dummy_rast WHERE rid = 2;
+
+ b1pixtyp
+----------
+ 2BUI</programlisting>
+ <informaltable>
+ <tgroup cols="2">
+ <tbody>
+ <row>
+ <entry><informalfigure>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="images/st_mapalgebraexpr01.png" />
+ </imageobject>
+ <caption><para>original (column rast-view)</para></caption>
+ </mediaobject>
+ </informalfigure></entry>
+ <entry><informalfigure>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="images/st_mapalgebraexpr02.png" />
+ </imageobject>
+ <caption><para>rast_view_ma</para></caption>
+ </mediaobject>
+ </informalfigure></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </informaltable>
+
+ <para>Create a new 3 band raster same pixel type from our original 3 band raster with first band altered by map algebra and remaining 2 bands unaltered.</para>
+ <programlisting>CREATE FUNCTION rast_plus_tan(pixel float, variadic args text[])
+RETURNS float
+AS
+$$
+BEGIN
+ RETURN tan(pixel) * pixel;
+END;
+$$
+LANGUAGE 'plpgsql';
+
+SELECT ST_AddBand(
+ ST_AddBand(
+ ST_AddBand(
+ ST_MakeEmptyRaster(rast_view),
+ ST_MapAlgebraFct(rast_view,1,NULL,'tan(rast)*rast')
+ ),
+ ST_Band(rast_view,2)
+ ),
+ ST_Band(rast_view, 3) As rast_view_ma
+)
+FROM wind
+WHERE rid=167;
+ </programlisting>
+ </refsection>
+
+ <refsection>
+ <title>See Also</title>
+ <para><xref linkend="RT_ST_MapAlgebraExpr" />, <xref linkend="RT_ST_BandPixelType" />, <xref linkend="RT_ST_GeoReference" />, <xref linkend="RT_ST_SetValue" /></para>
</refsection>
</refentry>
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