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Provide yet more common use case examples of ST_Value

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git-svn-id: http://svn.osgeo.org/postgis/trunk@5545 b70326c6-7e19-0410-871a-916f4a2858ee
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Regina Obe 2010-04-14 12:52:02 +00:00
parent 0fa018df23
commit 2d7bfed76c
1 changed files with 70 additions and 2 deletions
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70
doc/reference_wktraster.xml
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@ -1010,6 +1010,18 @@ FROM dummy_rast;
<title>Description</title>
<para>Returns the value of a given band in a given columnx, rowy pixel. Band numbers start at 1.</para>
<note><para>Note that although the X and Ys of these are not in coordinates of the spatial system,
you can get that by the following relationship.</para>
<para>Coordinate upper left of a row column
is:
ST_SetSRID(ST_Point(ST_UpperLeftX(rast) + ST_PixelSizeX(rast)*columnx, ST_UpperRightY(rast) + ST_PixelSizeX(rast)*columny), ST_SRID(rast))
</para>
<para>If you want the pixel box instead of the upper left point, you can use the ST_MakeEnvelop function and
translate it every x,y.</para>
<para>Also note that many of these examples particular the intersection example can be more
simply done with the planned functions that are not currently available.</para>
</note>
</refsection>
<refsection>
@ -1047,11 +1059,67 @@ WHERE rid = 2 AND x &lt;= ST_Width(rast) AND y &lt;= ST_Height(rast);
:
</programlisting>
<programlisting>
--- Get all values in bands 1,2,3 of each pixel same as above but returning the upper left point point of each pixel --
SELECT ST_AsText(ST_SetSRID(
ST_Point(ST_UpperLeftX(rast) + ST_PixelSizeX(rast)*x,
ST_UpperLeftY(rast) + ST_PixelSizeX(rast)*y),
ST_SRID(rast))) As uplpt
, ST_Value(rast, 1, x, y) As b1val,
ST_Value(rast, 2, x, y) As b2val, ST_Value(rast, 3, x, y) As b3val
FROM dummy_rast CROSS JOIN
generate_series(1,1000) As x CROSS JOIN generate_series(1,1000) As y
WHERE rid = 2 AND x &lt;= ST_Width(rast) AND y &lt;= ST_Height(rast);
uplpt | b1val | b2val | b3val
-----------------------------+-------+-------+-------
POINT(3427929.25 5793245.5) | 253 | 78 | 70
POINT(3427929.25 5793247) | 253 | 96 | 80
POINT(3427929.25 5793248.5) | 250 | 99 | 90
:
</programlisting>
<programlisting>
--- Get a polygon formed by union of all pixels
that fall in a particular value range and intersect particular polygon --
SELECT ST_AsText(ST_Union(pixpolyg)) As shadow
FROM (SELECT ST_Translate(ST_MakeEnvelope(
ST_UpperLeftX(rast), ST_UpperLeftY(rast),
ST_UpperLeftX(rast) + ST_PixelSizeX(rast),
ST_UpperLeftY(rast) + ST_PixelSizeY(rast), 0
), ST_PixelSizeX(rast)*x, ST_PixelSizeY(rast)*y
) As pixpolyg, ST_Value(rast, 1, x, y) As b1val
FROM dummy_rast CROSS JOIN
generate_series(1,1000) As x CROSS JOIN generate_series(1,1000) As y
WHERE rid = 2
AND x &lt;= ST_Width(rast) AND y &lt;= ST_Height(rast)) As foo
WHERE
ST_Intersects(
pixpolyg,
ST_GeomFromText('POLYGON ((3427935.6902608695 5793250.889478261,
3427932.0770434784 5793251.682173912,
3427931.9295652173 5793250.400956522,
3427933.0576086957 5793248.985, 3427933.518478261 5793249.192391304,
3427934.611826087 5793248.999913043, 3427935.6902608695 5793250.889478261))',0)
) AND b1val != 254;
shadow
------------------------------------------------------------------------------------
MULTIPOLYGON(((3427933.75 5793248.5,3427933.75 5793250,3427935.25 5793250,
3427935.25 5793248.5,3427933.75 5793248.5)),
((3427930.75 5793250,3427930.75 5793251.5,3427930.75 5793253,3427932.25 5793253,
3427932.25 5793251.5,3427932.25 5793250,3427930.75 5793250)),
((3427935.25 5793250,3427935.25 5793251.5,3427936.75 5793251.5,
3427936.75 5793250,3427935.25 5793250)))
</programlisting>
</refsection>
<refsection>
<title>See Also</title>
<para><xref linkend="RT_ST_NumBands" /></para>
<para><xref linkend="RT_ST_NumBands" />, <xref linkend="RT_ST_PixelSizeX" />,
, <xref linkend="RT_ST_PixelSizeY" />, <xref linkend="RT_ST_UpperLeftX" />,
<xref linkend="RT_ST_UpperLeftY" />, <xref linkend="RT_ST_SRID" />, <xref linkend="ST_AsText" />,
, <xref linkend="ST_Point" />, <xref linkend="ST_MakeEnvelope" />,
<xref linkend="ST_Intersects" /></para>
</refsection>
</refentry>