[postgis-users] Cut lines with polygon

[Alexander Strunck]

Hello

i checked if its a rendering problem. but that´s not it. for example i have a polygon with a hole in it and one line yust go through this hole...

how can i find the poylgon that throughs this error? i have no idea...


alex


 
-------- Original-Nachricht --------
> Datum: Mon, 5 Oct 2009 14:57:44 +0200
> Von: Brian Modra <brian at zwartberg.com>
> An: PostGIS Users Discussion <postgis-users at postgis.refractions.net>
> Betreff: Re: [postgis-users] Cut lines with polygon

> 2009/10/5 Alexander Strunck <A.Strunck at gmx.net>:
> > Hello
> >
> > i am really new to postgis and i try to cut lines with a polygon. the
> sql statement is
> >
> > create table osm_line_in_dorfring2_5_10 as
> > SELECT b.way_id, b.geom,
> > Intersection ( g.geom, b.geom )
> >  FROM stadtdorfbuffer2_5_10 AS g, osm_line AS b
> >  WHERE IsEmpty ( Intersection ( g.geom, b.geom ) ) = FALSE;
> >
> > but when i look at the result the lines are not cut by the polygon. the
> lines go a little bit over the borders of the polygon. Why is that?
> 
> Have you checked the coords and done the maths (manually) to see if
> the intersection points are wrong? Maybe its just a rendering problem
> in whatever you are using to view them?
> 
> > the second problem ist when i want to do the same thing with two
> different polygon tables. i get the error
> > NOTICE:  TopologyException: found non-noded intersection between
> 8.18405 48.9483, 8.18366 48.9481 and 8.18285 48.947, 8.18933 48.9551 8.18381
> 48.9482
> > ERROR:  GEOS Intersection() threw an error!
> >
> > ********** Fehler **********
> >
> > ERROR: GEOS Intersection() threw an error!
> > SQL Status:XX000
> 
> See if you can find the polygon that its throwing this for, and view
> it to see if there is something obvious about the topology.
> 
> >
> > i tested the polygon tables with ST_IsValid and everything seems to be
> all right.
> >
> > does someone have any suggestions?
> >
> > thx in advance
> >
> > alex
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> 
> 
> 
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