Thanks for your help Brent. My OS is Debian.
On Fri, Feb 1, 2013 at 10:57 AM, <[email protected]> wrote: > Hi Rebecca, > > Sounds like you are doing this in a script, but you didn't specify your OS. > > If so, then as each iteration completes, you can accumulate the id's of > the polygons dealt to already, & test against this list to avoid creating > the duplicates. Either in a file or in a table. > > Along the lines of: > > for polygon in <list of polygon ids> do > if id not in list of unioned id's; then > add ids to be unioned in this iteration to the list of unioned ones > union them > end of if > move to next polygon id > > You might consider making the unioned polygons a multipolygon, just in > case some of them are. > > There are improved functions & performance with later versions of postgres > & postgis, so you might consider upgrading. > > HTH, > > Brent Wood > > > --- On *Fri, 2/1/13, Rebecca Clarke <[email protected]>* wrote: > > > From: Rebecca Clarke <[email protected]> > Subject: [postgis-users] Advice on Unioning Polygons > To: [email protected] > Date: Friday, February 1, 2013, 11:40 PM > > > Hi there > > Looking for some advice. > > I have a table with thousands of polygon records. > > I want to union all intersecting polygons that have the same attributes > into one polygon (So one record, rather than 10 or 20 etc.). > > Can anyone recommend the best way to do this. > > I can do a loop which goes through each record, unions its geometry with > the geometry's of the other matching records that intersect with it, then > move to the next record. Problem with this is that it creates > duplicate polygons when it comes to a record that has already been unioned > with a previous one record. I can easily delete any duplicate records > generated, but I'm wondering if there's a less long winded way. > > I hope I'm explaining myself correctly. > > My details are: > postgis 1.3.5 > PostgreSQL 8.3.8 > > Many thanks in advance. > > Rebecca > > > -----Inline Attachment Follows----- > > _______________________________________________ > postgis-users mailing list > [email protected]<http://mc/[email protected]> > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > >
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