[postgis-users] k-nearest Polygons

[Skye Book]

http://postgis.refractions.net/docs/geometry_distance_box.html
http://postgis.refractions.net/docs/geometry_distance_centroid.html

Both operators are insanely handy and very simple to use :)

Skye Book
http://skyebook.net -- @sbook <https://twitter.com/sbook>

On Oct 27, 2012, at 8:34 AM, Ed Linde <edolinde at gmail.com> wrote:

Could you please link me to the postgis 2.0 section in the docs that talks
about
using <#> and <-> ? Those operators look quite handy to me :)

On Sat, Oct 27, 2012 at 3:32 PM, Sandro Santilli <strk at keybit.net> wrote:

> On Sat, Oct 27, 2012 at 03:27:13PM +0200, Ed Linde wrote:
> > Thanks. Just to clear things up, :point_or_poly bind variable needs a
> > "geometry"
> > type passed in to it, right?
>
> Yes
>
> --strk;
>
> >
> > Thanks,
> > Ed
> >
> > On Sat, Oct 27, 2012 at 1:57 PM, Sandro Santilli <strk at keybit.net>
> wrote:
> >
> > > On Sat, Oct 27, 2012 at 01:37:05PM +0200, Ed Linde wrote:
> > >
> > > > Is there a way to know for a user defined "k" what the k-nearest
> polygons
> > > > to a given polygon or point are in postgis?
> > >
> > > -- Simple answer:
> > > SELECT gid from polygons
> > >  ORDER BY ST_Distance(the_geom, :point_or_poly)
> > >  LIMIT :k;
> > >
> > > More complex: if you have PostGIS-2.0 and need
> > > more speed the following versions do use a spatial
> > > index, if defined on "polygons":
> > >
> > > -- k nearest to bounding box of polygons:
> > > SELECT gid FROM polygons
> > >  ORDER BY the_geom <#> :point_or_poly
> > >  LIMIT :k;
> > >
> > > -- k nearest to polygon center:
> > > SELECT gid FROM polygons
> > >  ORDER BY the_geom <-> :point_or_poly
> > >  LIMIT :k;
> > >
> > > -- k nearest to polygon shape:
> > > -- NOTE: assumes the k closest objects
> > > --       are among the k*10 objects
> > > --       closer to boundingbox
> > > --
> > > WITH k_times_10_closer AS (
> > >   SELECT gid, the_geom FROM polygons
> > >    ORDER BY the_geom <#> :point_or_poly
> > >    LIMIT :k*10
> > > )
> > > SELECT gid from k_times_10_closer
> > >  ORDER BY ST_Distance(the_geom, :point_or_poly)
> > >  LIMIT :k;
> > >
> > > --strk;
> > >
> > >  http://www.cartodb.com - Map, analyze and build applications with
> your
> > > data
> > >
> > >                                        ~~ http://strk.keybit.net
> > >
> > > _______________________________________________
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> > >
>
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>
>
> --
>
>  http://www.cartodb.com - Map, analyze and build applications with your
> data
>
>                                        ~~ http://strk.keybit.net
>
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