RE: [postgis-users] WHERE POINT @ the_geom; returning two polygons/zip codes instead of one

[Matt Farley]

Thanks Steve, worked like a charm, you were right on.

I use the Contains function now:

SELECT zip FROM zipcodes WHERE POINT '(-121.447,38.570264)' @ the_geom AND
Contains(the_geom, POINT '(-121.446,38.570264)'); 

I believe the @ gives me an index to speed things up.

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Steve Wormley
Sent: Wednesday, August 24, 2005 3:35 PM
To: mfarley at sac-yolomvcd.com, PostGIS Users Discussion
Subject: Re: [postgis-users] WHERE POINT @ the_geom; returning two polygons/zip codes instead of one


On 2005-08-24 14:53, "Matt Farley" <mfarley at sac-yolomvcd.com> wrote:

> SELECT zip FROM zipcodes WHERE POINT '(-121.447,38.570264)' @ 
> the_geom;  - Returns two zip codes, 95816 and 95819
> 
> However
> (a 0.001 longitude change to the east)
> SELECT zip FROM zipcodes WHERE POINT '(-121.446,38.570264)' @ 
> the_geom; - Returns zip code 95819 properly
> 
> Both points are in 95819 and are near the border of 95816.
> 
> Any idea why the first query is returning both 95816 and 95819 -- the 
> point should only be found in 95819.

If the areas you imported are not exactly square then their bounding boxes may overlap and thus the @ operator will return multiple matches.

You'll need to use Intersects or Within or distance(a,b) = 0
to determine exactly which zip code they are in.

For speed you'll need an indexable query for your geometry index (I believe @ counts) before you use the more expensive Intersects query.


-Steve




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