[postgis-users] k-nearest Polygons

[Ed Linde]

thanks.

On Sat, Oct 27, 2012 at 4:42 PM, Skye Book <skye.book at gmail.com> wrote:

> 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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