[postgis-users] unioning a buffer - bug?

[Kevin Neufeld]

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;

SELECT count(*) FROM results;
SELECT ST_Summary(the_geom) FROM results;

Unioning a buffer shouldn't be problematic:

SELECT ST_AsText(
   ST_Union(
     ST_Buffer(column1, 0.1)
   )
)
FROM (VALUES
   ('POLYGON((1 1, 1 2, 2 2, 1 1))'::geometry),
   ('POLYGON((1 1, 2 2, 2 1, 1 1))'::geometry)
) as v;

POLYGON ((
         1 0.9,
         0.980490967798387 0.901921471959677,
         0.961731656763491 0.907612046748871,
         0.96173165676349 0.907612046748872,
         0.954928240996994 0.911248548238567,
         0.94444297669804 0.916853038769746,
         0.929289321881345 0.929289321881345,
         0.929289321881345 0.929289321881346,
         0.916853038769745 0.94444297669804,
         0.90817310697871 0.960681986902375,
         0.907612046748871 0.961731656763491,
         0.901921471959677 0.980490967798388,
         0.900377969797711 0.996162408242473,
         0.9 1,
         0.9 2,
         0.901921471959677 2.01950903220161,
         0.907612046748871 2.03826834323651,
         0.916853038769745 2.05555702330196,
         0.929289321881345 2.07071067811865,
         0.94444297669804 2.08314696123025,
         0.961731656763491 2.09238795325113,
         0.980490967798387 2.09807852804032,
         1 2.1,
         2 2.1,
         2.01950903220161 2.09807852804032,
         2.03826834323651 2.09238795325113,
         2.05555702330196 2.08314696123025,
         2.07071067811865 2.07071067811865,
         2.08314696123025 2.05555702330196,
         2.09238795325113 2.03826834323651,
         2.09807852804032 2.01950903220161,
         2.1 2,
         2.1 1,
         2.09807852804032 0.980490967798387,
         2.09238795325113 0.961731656763491,
         2.08314696123025 0.94444297669804,
         2.07071067811865 0.929289321881345,
         2.05555702330196 0.916853038769745,
         2.03826834323651 0.907612046748871,
         2.01950903220161 0.901921471959677,
         2 0.9,
         1 0.9
     ))

-- 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
>
>
> _______________________________________________
> postgis-users mailing list
> postgis-users at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>    
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