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List:       postgis-users
Subject:    Re: [postgis-users] Decomposing Multiploygon
From:       chodgson () refractions ! net
Date:       2003-12-17 17:53:35
Message-ID: 1071683615.3fe0981f70ee0 () hydra
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Try using:

SELECT gmi_cntry FROM Countries 
WHERE the_geom && GeometryFromText( 'POINT(-105.0 52.0)', -1 )
  AND distance( the_geom, GeometryFromText( 'POINT(-105.0 52.0)', -1 ) ) = 0;

See http://postgis.refractions.net/docs/x541.html for more info.

HTH.
Chris


Quoting Ralph Mason <ralph.mason@telogis.com>:

> Thanks for the answer, that did what I need however the performance is
> very poor.
> 
> To find the couniries takes 20 ms
> 
> SELECT gmi_cntry from countries where
> the_geom ~= GeometryFromText('POINT(-105.0 52.0)',-1)
> 
> But
> 
> SELECT gmi_cntry from Countries where
> the_geom ~= GeometryFromText('POINT(-105.0 52.0)',-1) and
> contains(the_geom ,GeometryFromText('POINT(-105.0 52.0)',-1))
> 
> Takes 450 ms which seems like a huge difference.
> 
> Is there any way to improve this performance?
> 
> Thanks
> Ralph
> 
> 
> strk wrote:
> 
> >See the Intersects(geometry, geometry) function.
> >You need GEOS support compiled in.
> >
> >--strk;
> >
> >ralph.mason wrote:
> >
> >
> >>I am new to postgis and spatial data so I apologies in advance if this
> >>is covered already.  Google didn't turn up anything.
> >>
> >>I have a shape file of country outlines, each country is a multipolygon.
> >>
> >>I imported this using shp2postgis and created an index on the geometry
> >>column.  So far so good.
> >>
> >>However, as the a search is done on the bounding box of the multi
> >>polygon I get more than one country returned to many searches.  Eg
> >>querying in canada will return Canada, USA (because of the alaska ,
> >>mainland box), and Russia.
> >>
> >>So - Is there a way to query for records that contain the point in one
> >>of the polygons in the multipolygon?  Or do I need to decompose the
> >>multipolygon to a polygons?
> >>
> >>Assuming I need to decompose, is there a utility that can do this (I
> >>guess one could write a postgres function to do it)
> >>
> >>Thanks for any help
> >>Ralph
> >>
> >>
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> >>
> >>
> >
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> >
> >
> >
> >
> 
> 
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