[postgis-users] Strange behavior

[Paragon Corporation]

ST_AsText rounds data so what you get back is not to the precision actually
stored in your database.
 
Try using
ST_DWithin instead and adding in a small amount of buffer e.g.
ST_DWithin(geom, your_point,0.00001)
 
playing around with the distance.
 
We never rely on intersects for point - line checks because if you have
floating point junk it really screws up your calculations.
 
Leo and Regina
http://www.postgis.us

  _____  

From: postgis-users-bounces at lists.osgeo.org
[mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Richard Cernava
Sent: Friday, May 17, 2013 7:40 PM
To: postgis-users at lists.osgeo.org
Subject: [postgis-users] Strange behavior


I'm trying to query if a point is present inside a MultiLineString. When I
run the following query I get very strange results in my opinion. If someone
could elaborate as to what's going on it would be very much appreciated!  

>From this query I get a false and a true on the identical data. First I
check to see if the_geom intersects with my point and receive false. Second
I take the_geom and convert it to text and then compare it with my point
using ST_GeomFromText and get true. How is this possible? I've outputted the
result from the statement below.


SELECT fullname, ST_X(ST_StartPoint(ST_LineMerge(the_geom))),
ST_Y(ST_StartPoint(ST_LineMerge(the_geom))),
ST_AsText(the_geom) AS text,
ST_Intersects(the_geom, ST_GeomFromText('POINT(-122.837109 45.537746)',
4269)) AS fromdb,
ST_Intersects(ST_GeomFromText(ST_AsText(the_geom), 4269),
ST_GeomFromText('POINT(-122.837109 45.537746)', 4269)) AS fromtxt
from tiger_data.or_edges where   fullname like 'NW Norwich St' limit 1


"NW Norwich St";-122.837109;45.537746;"MULTILINESTRING((-122.837109
45.537746,-122.837253 45.537684,-122.837718 45.537368,-122.837829
45.537288,-122.838081 45.537108,-122.838169 45.537049))";f;t



-- 
-Richard 
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