[postgis-users] Help: CREATE TABLE <y> AS SELECT INTERSECTION(..., ...) ...
James G Wilkinson
jgw at alpinegeophysics.com
Mon Dec 13 14:47:04 PST 2004
I am new to PostGIS but not new to GIS in general having been an
ARC/Info user for sometime. I am trying to create a new geometry from the
intersection of two other MULTIPOLYGON geometries:
Coverage #1 (us_states) -- United States state boundaries
Coverage #2 (grid) -- a regularized grid of cells where each grid cell is
12,000 by 12,000 meters in size. There are 168 grid cells in the east-west
direction and 177 grid cell in the north-south direction.
Each coverage has the proper (and same) PROJ4 map projection parameters
defined in the PostGIS table 'spatial_ref_sys.' There are also appropriate
entries in the PostGIS table 'geometry_columns.' I have GiST indexes on the
geometries in each coverage, but I do not believe that they are used for
the SQL command that I am about to present.
I am pretty sure that the coverages are stored correctly in the PostgreSQL
data base since I can export both coverages to shape files using
'psql2shp' and import/display them into ARC/Info.
I am using PostgreSQL 7.4.1, PostGIS 0.9.0, and GEOS 2.1.0.
The SQL command that I use in my attempt to create a third geometry is as
beta=# CREATE TABLE test_int_gis AS SELECT INTERSECTION(t1.the_geom,
t2.the_geom) AS the_geom FROM grid t1, us_states t2;
After 24 hours on my Sun UltraSparc 160 (yeah, I know it is slow), the
is still running. I can do a similar operation in ARC/Info in about 20
Any assistance will be greatly appreciated.
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