[postgis-users] area and distance

[Paragon Corporation]

Chandler,
 
1) As Muhammad mentioned, you want to check to make sure your geometries are
in the same planar projection.  First verify you brought them in with a
specific projection
 
By doing a 
 
SELECT ST_SRID(geom), ST_AsText(geom) As wkt
FROM factory limit 1;
 
SELECT ST_SRID(geom)
FROM inner_area limit 1;
 
2) Your polygon may also be invalid in which case ST_Within will always
return false, do a 
 
SELECT ST_IsValid(geom)
FROM inner_area As i
WHERE i.name = 'Dewsbury'
 
3) The casing of the name may be different in which case query 2 will return
no records.
e.g i.name = 'DEWSBURY'  is not the same as i.name = 'Dewsbury'
 
though it often is if you are used to working with SQL Server and other
databases.
 
Hope that helps,
Regina
http://www.postgis.us
 

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Muhammad
Imran
Sent: Thursday, August 02, 2012 5:46 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] area and distance


Hi Chandler,

Did you check projection system of the both Geometries? Just to make sure,
use ST_TRANSFORM as inner function.

regards 

Muhammad Imran

--- On Fri, 8/3/12, CHANDLER DOUGLAS COLEMAN
<CHANDLER.D.COLEMAN at stu.mmu.ac.uk> wrote:




From: CHANDLER DOUGLAS COLEMAN <CHANDLER.D.COLEMAN at stu.mmu.ac.uk>
Subject: [postgis-users] area and distance
To: "postgis-users at postgis.refractions.net"
<postgis-users at postgis.refractions.net>
Date: Friday, August 3, 2012, 3:01 AM


Hello,
I am a newbie to PostGIS.  I am hoping some one can explain to me why the
following simple query doesn't return any info:

SELECT f.fact_name
FROM factory AS f, inner_area AS i
WHERE i.name = 'Dewsbury'
AND ST_WITHIN (f.geom,i.geom);

I have geom in as a column and I have 'Dewsbury' as a polygon record in
inner_area and there are 5 records in factory that fall within this polygon.
But the resulting table shows that none were selected.

My assumption here is that the SQL statement is correct, but that something
is wrong with the tables:  could it be how I imported the two tables from
shapefiles.

Thanks,
Chandler


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