Thank you for all the answers. I did not try the topology, as I need to study its implementation a little better.
I did not found the st_cleanpolygon function and using (St_Buffer, 0) did not worked: The dilate\erode visually corrects the problem, but of course introduce a small rounding in the angle introducing a small overlaping with other adjacent polygons... I guess that the tolerance with the GEOS PrecisionModel would be nice, I think that is the method used by ArcGIS products to "insure" geometry "topology" after aggregation operations. Any more ideas? Alexandre Neto On Fri, Oct 26, 2012 at 8:40 AM, Dave Potts <dave.po...@pinan.co.uk> wrote: > Have you considered curve smoothing or apply a small buffer around the > orginal data/ > > Sandro Santilli wrote: > > It will be _very_ slow. > > So much that you may prefer to make the topology persistent. > > > > Another approach I'd like to see implemented would be to expose a > > tolerance > > to the GEOS implemented functions. Basically exposing the GEOS > > PrecisionModel. By doing that you could specify a tolerance in the > overlay > > operations and the result should never have gaps bigger than the given > > tolerance. > > > > --strk; > > > > On Thu, Oct 25, 2012 at 10:28:19AM -0700, pcr...@pcreso.com wrote: > >> My impression is that working topologies is slow, especially with large > >> datasets - lots of computation involved. > >> > >> How effective would this be with hundreds of thousands or millions or > >> small polygons? > >> > >> Just running ST_Union() takes hours to days. > >> > >> Thanks > >> > >> Brent Wood > >> > >> --- On Fri, 10/26/12, Sandro Santilli <s...@keybit.net> wrote: > >> > >> From: Sandro Santilli <s...@keybit.net> > >> Subject: Re: [postgis-users] How to eliminate small gaps produced by > >> ST_union? > >> To: "PostGIS Users Discussion" <postgis-users@postgis.refractions.net> > >> Date: Friday, October 26, 2012, 6:04 AM > >> > >> You may try to construct a topology within PostGIS-2.0, using > >> a small tolerance, and then get the geometries back. > >> > >> --strk; > >> > >> On Thu, Oct 25, 2012 at 05:54:05PM +0100, Alexandre Neto wrote: > >> > I'm trying to Aggregate\Dissolve a set of adjacent, but not touching > >> > polygons in Postgis. The geometries were created editing the Postgis > >> table > >> > in QGIS created, with snapping and avoid overlap in the layer. > >> > > >> > I used ST_Union like this: > >> > > >> > SELECT ST_Union(the_geom) > >> > FROM table; > >> > > >> > Small gaps similar to lines appear in the result. This happens when > >> the > >> > adjacent polygons do not share the exact same vertices. > >> > > >> > [image: Inline image 2] > >> > Is there a way to eliminate this "gaps" or "small angles" within > >> Postgis? > >> > > >> > I know that v.clean in GRASS can eliminate small angles, and correct > >> > topology, but that would mean I needed to copy the features to GRASS, > >> > correct them and copy it back to Postgis. > >> > > >> > Thanks in advance, > >> > > >> > Alexandre Neto > >> > >> > >> _______________________________________________ > >> 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 > > > > > > -- > > > > http://www.cartodb.com - Map, analyze and build applications with your > > data > > > > ~~ http://strk.keybit.net > > > > _______________________________________________ > > 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 >
_______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
