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

[Paragon Corporation]

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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