The TopologyException is telling you exactly where the error occurs. I
would try subsetting your date to just the area around the give location
(and say make it 50% larger). Then try the "noding" query again and see
if it gives the same result.
It is unusual for ST_Union to find a problem when noding linework, but
it can happen due to precision issues. Another thing you can try is to
reduce the precision of your data slightly (using snap-to-grid). This
sometimes "jiggles" things enough that the noding will work.
These kind of precision issues usually happen because there are line
segments in adjacent polygons which are *nearly but not precisely*
parallel. This in turn happens when you have data which looks like a
polygonal coverage but which isn't in fact fully noded together. Is
this possibly what your data looks like?
If this all still fails, consider sending this to us as 2 shapefiles to
have a look at.
Chris Hermansen wrote:
Hi Kevin;
Sorry to take so long to get back on this!
How "isolated" do you want it? What I have right now is a three polygon
table that I wish to overlay on a 3378 polygon table.
Meantime, I'm working on making the problem smaller...
Kevin Neufeld wrote:
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!
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
