[postgis-users] noding problem

[Kevin Neufeld]

Can you isolate the geometry that is causing the error?  If geos is 
broken, it would be nice to have a test case.
IE. Try noding half the lines at a time, then try noding half of a half, 
etc...

-- Kevin

Chris Hermansen wrote:
> Hi folks;
>
> I posted something a few days back on a noding problem I'm having, and
> received no answer.  At this point I have more details and I think there
> is something seriously wrong.
>
> This is Postgis 1.3.1 and GEOS 3.0.0rc4.
>
> The Postgis Wiki has an example of putting two somewhat overlapping
> polygon networks together:
>
> http://www.postgis.org/support/wiki/index.php?ExamplesOverlayTables
>
> Basically, two tables of polygons are converted into linestrings and put
> in a third table.
>
> Then, the table of linestrings is noded; in the Wiki, the code given is:
>
> CREATE TEMP TABLE noded_lines AS
>    SELECT St_Union(the_geom) AS the_geom
>    FROM all_lines;
>
> Right, my problem!  I have two tables with multi-polygons.  I convert
> them to polygons.  I use isValid() on their geometries to make sure that
> they are in good shape.
>
> Then!  I run the "noding query" - which I might add takes a
> loooooooooooooooong time - and in the end I see:
>
> dustin=# create temp table step2 as
> dustin-# select st_union(geom) as geom from step1;
> NOTICE:  TopologyException: found non-noded intersection between
> 1.40568e+06 507100, 1.40568e+06 507100 and 1.40568e+06 507100,
> 1.40568e+06 507100 1.40568e+06 507100
> ERROR:  GEOS union() threw an error!
>
> OK, now to me this doesn't seem at all fair!  If the st_union() command
> is supposed to node the linework then WHY is complaining about non-noded
> intersections?
>
> Thanks in advance for any light you can shed on this!
>
>