PostGIS
Name
ST_Intersection — Returns a raster or a set of geometry-pixelvalue pairs representing the shared portion of two rasters or the geometrical intersection of a vectorization of the raster and a geometry.
Synopsis
+setof geomval +ST_Intersection(+`geometry `+geom, raster
rast, integer band_num=1`)`;
+setof geomval +ST_Intersection(+`raster `+rast, geometry
geom`)`;
+setof geomval +ST_Intersection(+`raster `+rast, integer
band, geometry geomin`)`;
+raster +ST_Intersection(+`raster `+rast1, raster rast2,
double precision[] nodataval`)`;
+raster +ST_Intersection(+`raster `+rast1, raster rast2,
text returnband, double precision[] nodataval`)`;
+raster +ST_Intersection(+`raster `+rast1, integer
band1, raster rast2, integer band2, double precision[]
nodataval`)`;
+raster +ST_Intersection(+`raster `+rast1, integer
band1, raster rast2, integer band2, text returnband,
double precision[] nodataval`)`;
Description
Returns a raster or a set of geometry-pixelvalue pairs representing the shared portion of two rasters or the geometrical intersection of a vectorization of the raster and a geometry.
The first three variants, returning a setof geomval, works in vector space. The raster is first vectorized (using ST_DumpAsPolygons) into a set of geomval rows and those rows are then intersected with the geometry using the ST_Intersection (geometry, geometry) PostGIS function. Geometries intersecting only with a nodata value area of a raster returns an empty geometry. They are normally excluded from the results by the proper usage of ST_Intersects in the WHERE clause.
You can access the geometry and the value parts of the resulting set of geomval by surrounding them with parenthesis and adding '.geom' or '.val' at the end of the expression. e.g. (ST_Intersection(rast, geom)).geom
The other variants, returning a raster, works in raster space. They are using the two rasters version of ST_MapAlgebraExpr to perform the intersection.
The extent of the resulting raster corresponds to the geometrical
intersection of the two raster extents. The resulting raster includes
'BAND1', 'BAND2' or 'BOTH' bands, following what is passed as the
returnband parameter. Nodata value areas present in any band results
in nodata value areas in every bands of the result. In other words, any
pixel intersecting with a nodata value pixel becomes a nodata value
pixel in the result.
Rasters resulting from ST_Intersection must have a nodata value assigned
for areas not intersecting. You can define or replace the nodata value
for any resulting band by providing a nodataval[] array of one or
two nodata values depending if you request 'BAND1', 'BAND2' or 'BOTH'
bands. The first value in the array replace the nodata value in the
first band and the second value replace the nodata value in the second
band. If one input band do not have a nodata value defined and none are
provided as an array, one is chosen using the ST_MinPossibleValue
function. All variant accepting an array of nodata value can also accept
a single value which will be assigned to each requested band.
In all variants, if no band number is specified band 1 is assumed. If you need an intersection between a raster and geometry that returns a raster, refer to ST_Clip.
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Enhanced: 2.0.0 - Intersection in the raster space was introduced. In earlier pre-2.0.0 versions, only intersection performed in vector space were supported.
Examples: Geometry, Raster — resulting in geometry vals
SELECT
foo.rid,
foo.gid,
ST_AsText((foo.geomval).geom) As geomwkt,
(foo.geomval).val
FROM (
SELECT
A.rid,
g.gid,
ST_Intersection(A.rast, g.geom) As geomval
FROM dummy_rast AS A
CROSS JOIN (
VALUES
(1, ST_Point(3427928, 5793243.85) ),
(2, ST_GeomFromText('LINESTRING(3427927.85 5793243.75,3427927.8 5793243.75,3427927.8 5793243.8)')),
(3, ST_GeomFromText('LINESTRING(1 2, 3 4)'))
) As g(gid,geom)
WHERE A.rid = 2
) As foo;
rid | gid | geomwkt | val
-----+-----+---------------------------------------------------------------------------------------------
2 | 1 | POINT(3427928 5793243.85) | 249
2 | 1 | POINT(3427928 5793243.85) | 253
2 | 2 | POINT(3427927.85 5793243.75) | 254
2 | 2 | POINT(3427927.8 5793243.8) | 251
2 | 2 | POINT(3427927.8 5793243.8) | 253
2 | 2 | LINESTRING(3427927.8 5793243.75,3427927.8 5793243.8) | 252
2 | 2 | MULTILINESTRING((3427927.8 5793243.8,3427927.8 5793243.75),...) | 250
2 | 3 | GEOMETRYCOLLECTION EMPTY