PostGIS
Name
ST_Union — Returns the union of a set of raster tiles into a single raster composed of 1 or more bands.
Synopsis
raster +`*`+ST_Union*(`setof raster `rast`)`;
raster +`*`+ST_Union*(`setof raster `rast, unionarg[]
unionargset`)`;
raster +`*`+ST_Union*(`setof raster `rast, integer
nband`)`;
raster +`*`+ST_Union*(`setof raster `rast, text
uniontype`)`;
raster +`*`+ST_Union*(`setof raster `rast, integer nband,
text uniontype`)`;
Description
Returns the union of a set of raster tiles into a single raster composed
of at least one band. The resulting raster’s extent is the extent of the
whole set. In the case of intersection, the resulting value is defined
by uniontype which is one of the following: LAST (default), FIRST,
MIN, MAX, COUNT, SUM, MEAN, RANGE.
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Availability: 2.0.0
Enhanced: 2.1.0 Improved Speed (fully C-Based).
Availability: 2.1.0 ST_Union(rast, unionarg) variant was introduced.
Enhanced: 2.1.0 ST_Union(rast) (variant 1) unions all bands of all input rasters. Prior versions of PostGIS assumed the first band.
Enhanced: 2.1.0 ST_Union(rast, uniontype) (variant 4) unions all bands of all input rasters.
Examples: Reconstitute a single band chunked raster tile
-- this creates a single band from first band of raster tiles
-- that form the original file system tile
SELECT filename, ST_Union(rast,1) As file_rast
FROM sometable WHERE filename IN('dem01', 'dem02') GROUP BY filename;Examples: Return a multi-band raster that is the union of tiles intersecting geometry
-- this creates a multi band raster collecting all the tiles that intersect a line
-- Note: In 2.0, this would have just returned a single band raster
-- , new union works on all bands by default
-- this is equivalent to unionarg: ARRAY[ROW(1, 'LAST'), ROW(2, 'LAST'), ROW(3, 'LAST')]::unionarg[]
SELECT ST_Union(rast)
FROM aerials.boston
WHERE ST_Intersects(rast, ST_GeomFromText('LINESTRING(230486 887771, 230500 88772)',26986) );Examples: Return a multi-band raster that is the union of tiles intersecting geometry
Here we use the longer syntax if we only wanted a subset of bands or we want to change order of bands
-- this creates a multi band raster collecting all the tiles that intersect a line
SELECT ST_Union(rast,ARRAY[ROW(2, 'LAST'), ROW(1, 'LAST'), ROW(3, 'LAST')]::unionarg[])
FROM aerials.boston
WHERE ST_Intersects(rast, ST_GeomFromText('LINESTRING(230486 887771, 230500 88772)',26986) );