[postgis-users] Distance Query Performance
alan_cunnane at yahoo.co.uk
Tue Jul 10 14:01:51 PDT 2007
I have two tables that contain bus stop related data and I am trying to pregenerate another table containing each bus stops that is located within 200 metres to each other. I have a spatial column with British national grid coordinates in the bus_stops1 table and am using this query to get the distance between each stop:
CREATE table topology (stop_a, stop_b, distance)
AS SELECT DISTINCT a.stop_reference, b.stop_reference, distance(a.east_north, b.east_north)
FROM bus_stops1 a, bus_stops1 b, service1 c, service1 d
WHERE distance(a.east_north, b.east_north) < 200
AND a.stop_reference <> b.stop_reference
AND c.service_id <> d.service_id
ORDER BY distance(a.east_north, b.east_north);
Now the problem it just seems to either stall or else take a long long time to complete this query, is this normal?? There are about 15,000 rows in the table bus_stops1 with a cooridnate for each of those stops. Is there anything I am doing wrong or that I can do to speed this up? I have built a gist index on the spatial column already and on the foreign keys.
Thanks for your help
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