Hi Steve, What indexes can I put on the linestring column? Is there an option of using a R-Tree index?
Thanks, Ed On Wed, Jun 6, 2012 at 4:54 PM, Stephen Woodbridge <wood...@swoodbridge.com>wrote: > On 6/6/2012 9:57 AM, Ed Linde wrote: > >> Hi All, >> Simple question. I have a table with half a million linestring >> geometries, and I want to compute the >> intersection points and also the linestring pairs that intersect with >> each other. >> How can I do this? Is there an index that can avoid having to do a >> self-join and computing >> the intersections? >> > > Create a spatial index on your table of linestrings and do a self join > > select a.gid, b.gid, st_intersection(a.the_geom, b.the_geom) > from linestrings a, linestrings b > where a.the_geom && b.the_geom and st_intersects(a.the_geom, b.the_geom); > > You might get away with using this instead for the where: > > where st_dwithin(a.the_geom, b.the_geom, 0.0); > > Which might be faster. > > The result will potentially be a collection if there is more then one > intersection and/or might be a linestring if the intersection is an overlap > along some part of the two strings. > > -Steve > > ______________________________**_________________ > postgis-users mailing list > postgis-users@postgis.**refractions.net<postgis-users@postgis.refractions.net> > http://postgis.refractions.**net/mailman/listinfo/postgis-**users<http://postgis.refractions.net/mailman/listinfo/postgis-users> >
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