[postgis-users] how to find smallest containing region

[Obe, Regina]

Well if you make your linestrings actually polygons, that would be the
first step.

Then I think something like this might work (not it would be much more
efficient if you create a table with polygons instead having linestrings
and put an index on that.

If you really have line strings and not polygons - do this before the
below query
SELECT gid, ST_MakePolygon(the_geom) As the_geom INTO poly
FROM linestring;

CREATE INDEX idx_poly_gist
  ON poly
  USING gist
  (the_geom);
ALTER TABLE poly CLUSTER ON idx_poly_gist;

--then do this

SELECT DISTINCT ON(pt.gid)
	pt.gid, pt.the_geom as the_point, poly.gid as poly_gid,
poly.the_geom as encpolygon 
FROM points pt LEFT JOIN poly ON ST_Within(pt.the_geom, poly.the_geom)
ORDER BY
pt.gid, ST_Area(poly.the_geom);

Hope that helps,
Regina



-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Edward Q. Bridges
Sent: Sunday, July 13, 2008 8:22 AM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] how to find smallest containing region

Hello,

I have data stored as points and linearrings (i.e. closed polygons).  
Can someone suggest an efficient approach to finding the smallest 
enclosing region for a given point?

Thanks!
Ed

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