Re: [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@postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users

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