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List:       postgis-users
Subject:    Re: [postgis-users] Union and Intersection of Polygon layers
From:       Kevin Neufeld <kneufeld () refractions ! net>
Date:       2009-09-22 1:38:30
Message-ID: 4AB82A96.5060804 () refractions ! net
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The PostGIS wiki has some thoughts on overlays ...

http://trac.osgeo.org/postgis/wiki/UsersWikiExamplesOverlayTables

Paul Ramsey wrote:
> Union is trivial. Here's a query that generates a new set of polygons
> dissolved based on an attribute value:
> 
> create table newtable as select st_union(the_geom), attribute group by
> attribute;
> 
> Overlay is non-trivial, and I leave that to someone else to provide
> good SQL. The simple case of finding all the overlapping parts is
> easy, but filling in the non-overlapping parts is harder.
> 
> P
> 
> On Mon, Sep 21, 2009 at 3:32 PM, Ravi <ravivundavalli@yahoo.com> wrote:
> 
> > Hi,
> > am using other FOSS GIS GRASS and OpenJUMP for
> > Polygon layers Union
> > and Intersection (overlay)
> > are there similar functions in postGIS THE LATEST RELEASE
> > 
> > I have raised these issues some time before too.
> > http://postgis.refractions.net/pipermail/postgis-users/2008-May/019515.html
> > 
> > Ravi Kumar
> > 
> > 
> > 
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