[postgis-users] st_intersection error

nicklas.aven at jordogskog.no nicklas.aven at jordogskog.no
Tue Sep 15 03:50:09 PDT 2009

The problem is the vertex represented only in line 2 between your resulting line and point 'POINT(618971.85092967 251568.179431664) . Because of precision aspects it will never be exactly on the line causing st_intersection find only the point and line to be exactly the same place. /Nicklas

2009-09-15 Düster Horst wrote:

I do have 2 simple linestrings which partly have the same geometry (see attached dump and image). My aim is to detect the common part of these two linestrings with the following query:
select st_intersection(a.the_geom, b.the_geom), a.myid
>from aline1, aline2
But as the result I get a geometrycollection with one POINT and one LINESTING. I expected one linestring. Is it a bug??
>I'll appreciate any hints.
My system:
>Postgis 1.4.0
>Geos 3.1.1
>Postgres 8.3.6
Best regards
Dr. Horst Düster
>Stv. Amtschef / GIS-Koordinator 
Kanton Solothurn
>Bau- und Justizdepartement
>Amt für Geoinformation
>SO!GIS Koordination
>Rötistrasse 4
>CH-4501 Solothurn
Telefon ++41(0)32 627 25 32
>Telefax ++41(0)32 627 22 14
mailto:horst.duester at bd.so.ch
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