[postgis-users] Point in Polygon query tolerance?

[Frank Broniewski]

Dear list users

I am a beginner with postgis and have just inserted my first data into 
postgres database so my question might be a little bit naive ;-). Please bear 
with me ...

To my problem: I have a geology polygon table and a site point table. Now I 
want to find out the site's geology. I do the following query

SELECT name FROM geo.geology AS c, arch.operation AS p WHERE c.the_geom && 
p.op_centroid AND p.op_id = 20

for a single sample site. The query returns three rows, while it should be 
just one. Another site returns even five rows as result. I tested in QGIS 
both the geology and site table, they display fine. The point is about 90m 
away from the containing polygon border. I measured this with the QGIS 
distance tool.

Does anyone have an idea why I get three lines returned while it should be 
just one? Is there some kind of tolerance setting I can toggle? Is this 
a "bounding box" issue? If yes, how can I solve this? As far as I can tell, 
the polgons do not overlap, but I would not bet my head on it. I am a little 
bit lost here, so any help is greatly appreciated.

Greetings from Germany

Frank

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Frank Broniewski
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Email: frank at geo-dienstleistung.de
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