If you are saying that dump doesn't break your multi polygon into pieces, either _ dump has a bug (unlikely) _ you don't have a multipolygon but a geometry collection (try ST_Dump(ST_CollectionExtract(geom,2))) _you have an invalid simple polygon (try st_isvalid() ) _you have a simple polygon where interior rings should be stand alone polygon, use St_ringextract Cheers,
Rémi-C 2014-01-28 Hugues François <[email protected]> > What you say sounds very weird to me. I don't understand how postgis can > consider a multipolygon as a polygon. Could you provide us a test sample of > your data ? > > Hugues. > > > > > -----Original Message----- > From: [email protected] [mailto: > [email protected]] On Behalf Of Tom McCallum > Sent: Tuesday, January 28, 2014 3:25 PM > To: [email protected]; PostGIS Users Discussion > Subject: Re: [postgis-users] Removing tiny polygons > > Yes I just want the largest polygons. The problem being that when I > simplify the polygon it appears to need a lot more simplification due to > these islands rather than if it just did did one mainland polygon ( > asGeoJson comes in at 437 polygons rather than 1 polygon). Not sure why > GeoJson can split it into multiple polygons but Dump[] just hands me one. > > Was hoping to use ST_Area but currently cannot break down the single > polygon. > > Interestingly QGIS can, if I do single to multipart it can break down into > main landmass and islands. What might be an equivalent postgis method for > doing this? > > > On Mon, 27 Jan 2014 19:15:18 -0000, Morten Sickel <[email protected]> > wrote: > > > It depends on what you mean with "remove" - do you want to just have > > the large polygons without the area that is covered by the small ones > > or do you want to add the area of the small polygons onto one or more > > of the larges? (e.g. how one typically wants to handle shiver > > polygons) > > > > In the first case it is as easy as a query like > > > > select the_geom where ST_area(the_geom) > ... > > > > Morten > > > > > > Tom McCallum skrev: > >> Hi all, > >> > >> If I have a polygon geometry field which seems to be made up of a > >> large number of tiny polygons and some larger ones, what is the best > >> way to remove polygons below a certain size? Would I need to > >> preprocess this and save in a new table/record or can I dynamically > >> do it? > >> > >> Thanks > >> > >> Tom > >> _______________________________________________ > >> postgis-users mailing list > >> [email protected] > >> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > >> > > > > > > _______________________________________________ > > postgis-users mailing list > > [email protected] > > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > _______________________________________________ > postgis-users mailing list > [email protected] > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > _______________________________________________ > postgis-users mailing list > [email protected] > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users >
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