One of the new enhancements in PostGIS 2.1 and the one I'm most excited about so far is the new faster raster union functionality. Raster Unioning I think is one of the most important functions for raster especially if you have your tiles chunked since for certain cases, you are going to want to glue them back together again.
In PostGIS 2.0.1, the raster ST_Union function piggy-backed a little on plpgsql, in PostGIS 2.1.0, it has been completely reimplemented and reimplemented in C.
It's still going thru some optimizations, but as of PostGIS 2.1.0 r10361, you can expect union speed to be about 4-8 times faster. Here is an example. This example still uses ST_Clip which hasn't been optimized yet so you want see the complete speed improvement.
To test the speed difference, I used a MassGIS 2008 aerial tile I had converted from MrSid to JPEG and loaded with this command:
raster2pgsql -s 26986 -t 100x100 -F -I -Y 23128870.jpg test_100_100 | psql -U postgres -d testpostgis21 -h localhost -p 5432
You can download the test data from 23128870.zip. If you are on Windows and running 9.2 (32-bit/64-bit) or 9.0/9.1 postgresql 64-bit, Winnie the PostGIS windows build bot has fresh binaries you can experiment with
you can download from http://postgis.net/windows_downloads
This is I most favorite artsy query to run which produces an output:
SELECT ST_AddBand(NULL,ARRAY[ST_Union(rast,1), ST_Union(rast,2), ST_Union(rast,3) ])
FROM (SELECT ST_Clip(rast,geom) As rast
CROSS JOIN ST_Buffer(ST_GeomFromText('POINT(231237.436173996 887025.024778253)',26986),50, 'quad_segs=2') As geom
WHERE ST_Intersects(rast, geom ) ) As foo;
and takes about 4.5 seconds on PostGIS 2.0.1, PostgreSQL 9.2.1 windows 7 64-bit with default factory settings and has to run thru 16 tiles each tile being 100x100.
If you run this query in PostGIS 2.1.0, it goes down to about 1,560ms.
SELECT ST_Union(rast,ARRAY[ROW(1, 'LAST'), ROW(2, 'LAST'), ROW(3, 'LAST')]::unionarg)
FROM (SELECT ST_Clip(rast , geom) As rast
CROSS JOIN ST_Buffer(ST_GeomFromText('POINT(231234.436173996 887025.024778253)',26986),50, 'quad_segs=2') As geom
WHERE ST_Intersects(rast, geom ) ) As foo
Although the 2.0.1 syntax is still supported, the second query (preferred 2.1 syntax) runs about 300ms faster for this particular query.
The speed difference is more startling if we compare unclipped speeds. For unclipped speeds, the 2.1.0 ST_Union still finishes at about 1,560ms, while the
PostGIS 2.0.1 goes up to 6,712ms.
Continue reading "Waiting for PostGIS 2.1: Faster Raster Union"