reference was meant to be just an example table your grid is in. If you don't have any then you don't really need the inner join except for not having to repeat the same static geometry twice So below I defined a static geometry to represent by grid geom -- ST_Buffer(ST_Point(1,2),3) replace this with your grid polygon SELECT ST_Centroid(ST_Collect(ST_Intersection(r.the_geom,p.the_geom))) As the_centroid FROM tblpolygons As p INNER JOIN (SELECT ST_Buffer(ST_Point(1,2),3) As the_geom) As r ON ST_Intersects(r.the_geom, p.the_geom)
_____ From: [email protected] [mailto:[email protected]] On Behalf Of Bob Pawley Sent: Monday, April 20, 2009 12:05 PM To: PostGIS Users Discussion Subject: Re: [postgis-users] Reference Grid Hi Regina Thanks for the help. I don't understand " INNER JOIN reference As r ON". I get the error - > relation "reference" does not exist. It doesn't like my substitution for reference either. Bob Bob ----- Original Message ----- From: Paragon Corporation <mailto:[email protected]> To: 'PostGIS Users <mailto:[email protected]> Discussion' Sent: Sunday, April 19, 2009 8:58 PM Subject: RE: [postgis-users] Reference Grid Bob, Does the below help any. The below will give you the centroid of the portion of geometries that intersect a reference grid where the grid of the reference is defined by reference.the_geom SELECT r.gid, r.the_geom, ST_Centroid(ST_Collect(ST_Intersection(r.the_geom,p.the_geom))) As the_centroid FROM tblpolygons As p INNER JOIN reference As r ON ST_Intersects(p.the_geom, r.the_geom) GROUP BY r.gid, r.the_geom Hope that helps, Regina _____ From: [email protected] [mailto:[email protected]] On Behalf Of Bob Pawley Sent: Sunday, April 19, 2009 1:58 PM To: PostGIS Users Discussion Subject: [postgis-users] Reference Grid Hi I'm using a reference grid of small polygons. I have been trying to collect concurrent polygons into one geometry in order to establish the centroid of the region covered. I've tried a number of operations such as union, contains, accum etc. I haven't been successful. Can anyone give me some ideas?? Bob _____ _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
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