[postgis-users] ST_INTERSECT returns false, but should return true

[Satish Murthy]

That seems to be the right reason. Thanks :)

From: lr at pcorp.us
To: postgis-users at postgis.refractions.net
Date: Wed, 9 Dec 2009 20:29:48 -0500
Subject: Re: [postgis-users] ST_INTERSECT returns false,	but should return true










Satish,
AsText and AsEWKT only show the first 15 or 16 digits so I suspect 
your real geometries have more digits and are really off by a small 
amount.
 
To be sure use the ST_AsHexEWKB representation of the ST_AsEWKT 
 instead of and you will see the distance is probably > 0  
but very small.
 
 
Leo 



From: postgis-users-bounces at postgis.refractions.net 
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of 
Satish Murthy
Sent: Wednesday, December 09, 2009 11:28 
AM
To: postgis-users at postgis.refractions.net
Subject: 
[postgis-users] ST_INTERSECT returns false, but should return 
true


Hi,

I can't figure out why this is happening:

This works, returning true:
SELECT Intersects(
GeomFromEWKT('MULTILINESTRING((-26.9599999999939 -29.97 1 0,-26.9399999999976 -29.99 2 0),(-25.8599999999937 -29.97 1 0,-26.9399999999976 -29.99 2 0))'), 
    GeomFromEWKT('POINT(-26.9599999999939 -29.97 1 0)')) ;

If I select the same as geometries, it returns false
SELECT ST_Intersects(
   
(select geom1 from tab), 

    (select geom2 from tab)) ;


Weird thing is, 
   select ST_DISTANCE (geom1, geom2)
returns 3.51700710773038e-14

This behavior is not consistent - sometimes ST_INTERSECTS returns true correctly.

Can anyone suggest what might be the problem here?

Thanks,
Satish



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