[postgis-users] Cut lines with polygon

[Brian Modra]

2009/10/5 Alexander Strunck <A.Strunck at gmx.net>:
> 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...

take a look at this:
http://postgis.refractions.net/documentation/manual-svn/ch04.html#OGC_Validity

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

I assume they all have UIDs?
Do it iteratively:
start with one half of the table (limited by UID range)
If that throws the error, then try one half of that half, etc... unil
you are down to one polygon.

>
>
> 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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>>
>>
>>
>> --
>> Brian Modra   Land line: +27 23 5411 462
>> Mobile: +27 79 69 77 082
>> 5 Jan Louw Str, Prince Albert, 6930
>> Postal: P.O. Box 2, Prince Albert 6930
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-- 
Brian Modra   Land line: +27 23 5411 462
Mobile: +27 79 69 77 082
5 Jan Louw Str, Prince Albert, 6930
Postal: P.O. Box 2, Prince Albert 6930
South Africa
http://www.zwartberg.com/