Hi Lee,
Unfortunately, I can't duplicate your error. I can
st_union(st_buffer(geom, 0.1)) no problem ...
POLYGON ((
586801.773149238 4951692.01936019,
586801.773148314 4951692.01935961,
586773.455669237 4951674.0093102,
....
What version of GEOS are you running? As I've said, it works fine for me
running 3.2.2. Perhaps you need to upgrade?
Cheers,
Kevin
On 9/15/2010 12:09 PM, Lee wrote:
okay so I plotted those points that were in the topology exception
error, and narrowed it down to two adjacent polygons. So now I have:
select st_union(st_buffer(the_geom,0.1)) from
base.current_assessment_parcel where gid in (36,37)
(returns the topology exception)
Checking out those two parcels, they seem legit in qgis / arcview. (no
weird nodes that I can see).
Attached is the output from the following query: select gid,
st_asewkt(the_geom) from base.current_assessment_parcel where gid in
(36,37)
I'm relatively newbie to postgis, so can't see what might be causing
this, if someone could look at this for me?
unfortunately, I am on vacation starting tonight, and won't be
available to provide further details. If the answer is "your polygons
are just messed up" then so be it. These are from someone elses
shapefile. Just want to help if this is indeed a bug.
Thanks for your help Kevin.
Lee.
------------------------------------------------------------------------
*From:* Kevin Neufeld <[email protected]>
*To:* PostGIS Users Discussion <[email protected]>
*Sent:* Tue, September 14, 2010 10:49:25 PM
*Subject:* Re: [postgis-users] unioning a buffer - bug?
Interesting. Something sure sounds amiss. Are the results null? Is
there anything usual occurring at the TopologyException location? Is
your dataset large? Can you winnow it down to the few polygons that
might be causing the problem (this may be just the polygons around the
TopologyException location)? If so, you could paste the
representation of the geometries in PasteBin or something so we can
help you isolate the problem.
Also, what version of GEOS do you have installed?
SELECT PostGIS_Full_Version();
Cheers,
Kevin
On 9/14/2010 6:03 AM, Lee wrote:
Hi Kevin,
I assumed I have no results because when I load one of the working
queries as a view (eg. select st_buffer(the_geom,0.1)) in QGIS, or in
ArcGIS, I see all my results as I would expect, but when I modify the
query to st_union(st_buffer()), all my parcels disappear and I have a
blank canvas.
Also, with st_isvalid(st_union(st_buffer(the_geom,0.1))) returning
null (neither t nor f) I guess I just assumed. Anyways, results for
your suggestions are inline, below.
Thanks for your help. Any further ideas?
Lee.
------------------------------------------------------------------------
*From:* Kevin Neufeld <[email protected]>
*To:* [email protected]
*Sent:* Tue, September 14, 2010 12:12:46 AM
*Subject:* Re: [postgis-users] unioning a buffer - bug?
How are you determining you have no results?
Try:
CREATE TABLE results AS
SELECT st_union(st_buffer(the_geom,0.1)) as the_geom
FROM base.current_assessment_parcel;
NOTICE: TopologyException: found non-noded intersection between
586714 4.95189e+006, 586714 4.95189e+006 and 586714 4.95189e+006,
586739 4.9519e+006 586714 4.95189e+006
Query returned successfully with no result in 1078 ms.
SELECT count(*) FROM results;
1
SELECT ST_Summary(the_geom) FROM results;
This returns blank.
(snip)
-- Kevin
On 9/13/2010 7:07 AM, Lee wrote:
So after some googling I see similar problems, but no solutions posted.
I am trying to union a buffer, but the query is returning no
results. Here is ultimately what I would like to achieve:
select st_union(st_buffer(the_geom,0.1)) as the_geom from
base.current_assessment_parcel
Here are some troubleshooting steps I have taken to try narrow it down:
select st_isvalid(the_geom) a from base.current_assessment_parcel
group by a
TRUE
select st_isvalid(st_buffer(the_geom,0.1)) a from
base.current_assessment_parcel group by a
TRUE
select st_isvalid(st_union(the_geom)) from
base.current_assessment_parcel
TRUE
select st_isvalid(st_union(st_buffer(the_geom,0.1))) from
base.current_assessment_parcel
NOTICE: TopologyException: found non-noded intersection between
586714 4.95189e+006, 586714 4.95189e+006 and 586714 4.95189e+006,
586739 4.9519e+006 586714 4.95189e+006
Total query runtime: 859 ms.
1 row retrieved.
(returns blank record)
And just for fun
select st_isvalid(st_buffer(st_union(the_geom),0.1)) a from
base.current_assessment_parcel
TRUE
I guess my next step would be to try the snap to grid functions, but
the first query above should work, shouldn't it?
Any help appreciated. Thanks.
Lee
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