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
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