[postgis-users] Spatial query Help: points not in set of polygons

[Obe, Regina]

SELECT a.*
FROM point a LEFT JOIN polygons b
	ON (a.the_geom && b.the_geom
    and ST_distance(a.the_geom, b.the_geom) = 0.0)
WHERE b.the_geom IS NULL

or

SELECT a.*
FROM point a LEFT JOIN polygons b
	ON ST_Within(a.the_geom, b.the_geom)
WHERE b.the_geom IS NULL

I think the second one should be more efficient, but I haven't done any
benchmarks.

Hope that helps,
Regina


-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Stephen Woodbridge
Sent: Wednesday, January 23, 2008 10:27 PM
To: PostGIS Users Discussion
Subject: [postgis-users] Spatial query Help: points not in set of
polygons

Hi all,

I'm drawing a blank on setting up a query for this.

I have a tables points and a table of polygons. I need to find all the 
points that are not in any of the polygons.

select a.*
   from points a, polygons b
  where a.the_geom && b.the_geom
    and distance(a.the_geom, b.the_geom) > 0.0;

The problem with this is that if a point is in polygon A it will have a 
distance to polygon B, so this in no good.

I thought of doing something like:

select * from points
  where distance(the_geom, union((select the_geom from polygons))) >
0.0;

or

select * from points
  where distance(the_geom, collect((select the_geom from polygons))) >
0.0;

So is there a better way to do this. Seems like there should be. If not 
which of these would you suggest.

Thanks,
   -Steve
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