[postgis-users] Donut-Polygon

[Albert Krueger]

Thanks for your immediate answer. Exactly, I would like to filter by area. So your blog, Simon, was a very great help for me. 

Many thanks for your help.

Greetings! Albert

> Von: "Simon Greener" <simon at spatialdbadvisor.com>
> An: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
> Betreff: Re: [postgis-users] Donut-Polygon
> Datum: Fri, 06 Feb 2009 10:57:14 +1100

> Or, if you want to filter by area (POLYGON and MULTIPOLYGON), see this: <a
> target="_blank"
> href='http://www.spatialdbadvisor.com/postgis_tips_tricks/92/filtering-rings
> -in-polygon-postgis'>http://www.spatialdbadvisor.com/postgis_tips_tricks/92/
> filtering-rings-in-polygon-postgis</a>
> regards
> Simon
> On Fri, 06 Feb 2009 05:29:15 +1100, Kevin Neufeld
> <<a href=mailto:"kneufeld at refractions.net">kneufeld at refractions.net</a>> wrote:
> 
> > Use ST_DumpRings to extract the rings, then exclude the ones you don't
> want and then rebuild your polygon.
> > <a target="_blank"
> href='http://postgis.refractions.net/documentation/manual-svn/ST_DumpRings.h
> tml'>http://postgis.refractions.net/documentation/manual-svn/ST_DumpRings.ht
> ml</a>
> >
> > ie.
> > -- A polygon with 6 inner rings, we exclude all but rings 3 and 5
> > SELECT ST_AsText(ST_BuildArea(ST_Collect(geom))) AS the_geom
> > FROM (SELECT (ST_DumpRings(
> >      'POLYGON (( 0 0, 0 7, 10 7, 10 0, 0 0 ),
> >                ( 1 4, 3 4, 3 6, 1 6, 1 4 ),
> >                ( 4 4, 6 4, 6 6, 4 6, 4 4 ),
> >                ( 7 4, 9 4, 9 6, 7 6, 7 4 ),
> >                ( 1 1, 3 1, 3 3, 1 3, 1 1 ),
> >                ( 4 1, 6 1, 6 3, 4 3, 4 1 ),
> >                ( 7 1, 9 1, 9 3, 7 3, 7 1 )
> >                )'::geometry)).*) AS foo
> > WHERE NOT ( ARRAY[1,2,4,6] @> path );
> >
> >                                     the_geom
> >
> ----------------------------------------------------------------------------
> --
> >   POLYGON((0 0,0 7,10 7,10 0,0 0),(7 4,9 4,9 6,7 6,7 4),(4 1,6 1,6 3,4
> 3,4 1))
> > (1 row)
> >
> > Cheers,
> > Kevin
> >
> > Albert Krueger wrote:
> >> Hi at all,
> >>
> >> I have a Donut-Polygon with a number of Innerrings. Now I would like to
> >> delete some Innerrings. For Example I have a polygon with five
> >> Innerrings. ButI want to delete the second and the fourth Innerring. Has
> >> anyone an idea how I can get a polygon with only three Innerrings
> >> (1,3,5) then?
> >>
> >> Thank you!
> >>
> >> Best regards
> >>
> >> Albert
> >>
> >>
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