Sorry, replying to my self again!
Looks like the LEFT JOIN is working just fine. I was tripped up by the
fact that I have previously NULL'd some of the polygons that were
invalid and so all their respective points were listed as would be
expected. And secondly, by the fact that there are a lot more results
that I was expecting, but spot checking a few of the files in
ArcExplorer verified the results.
And it looks like this query does not support geomcollection in the
distance function, but only fails with some obsure message in the
message window of pgadmin3, but if I change the collect() to geomunion()
it works, but is much slower than the left join as would be expected.
select file, id, name
from points
where distance(the_geom, (select collect(the_geom) from polygons)) > 0.0';
-Steve
Stephen Woodbridge wrote:
Regina,
I think I spoke too soon. On closer inspection of the results it looks
like the query is returning all the points in the points table.
select a.file, a.id, a.name
from points a LEFT JOIN polygons b
ON (a.the_geom && b.the_geom
and distance(a.the_geom, b.the_geom) = 0.0)
where b.the_geom IS NULL
I think this has a logic issue, IF b.the_geom is NULL then the ON clause
must also be NULL. Does that work?
I also tried this query, which returned no points:
select file, id, name
from points
where distance(the_geom, (select collect(the_geom) from polygons)) > 0.0';
Any thoughts why this does not appear to work?
I'm going to try your other query and see if I get different results
with that.
Thanks,
-Steve
Obe, Regina wrote:
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: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] 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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