[postgis-users] Centroid 'Within'

[Paragon Corporation]

Sheara,
 
Here is a function we use that seems to work pretty well for our use-case.
 
CREATE OR REPLACE FUNCTION point_inside_geometry(param_geom geometry)
  RETURNS geometry AS
$$
  DECLARE 
     var_cent geometry := ST_Centroid(param_geom); 
     var_result geometry := var_cent;
  BEGIN
  -- If the centroid is outside the geometry then 
  -- calculate a box around centroid that is guaranteed to intersect the
geometry
  -- take the intersection of that and find point on surface of intersection
 IF NOT ST_Intersects(param_geom, var_cent) THEN
  var_result := ST_PointOnSurface(ST_Intersection(param_geom,
ST_Expand(var_cent, ST_Distance(var_cent,param_geom)*2) ));
 END IF;
 RETURN var_result;
  END;
  $$
  LANGUAGE plpgsql IMMUTABLE STRICT
  COST 100;
 
Regina and Leo
h <http://www.postgis.us> ttp://www.postgis.us

  _____  

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Sheara
Cohen
Sent: Wednesday, June 22, 2011 3:19 PM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] Centroid 'Within'



Hi All - I'm wondering if anyone has figured out a solution to converting a
polygon file to a centroid point file that produces centroids within the
polygons. Obviously, ST_Centroid doesn't produce centroids within the
polygon. And ST_PointOnSurface produces a point within that is only sort of
centroid-ish.

 

Any ideas would be great. Thank you!

 

~ Sheara

 

Sheara Cohen
Planner

C A L T H O R P E  A S S O C I A T E S
2095 ROSE STREET, SUITE 201, BERKELEY, CALIFORNIA, 94709 USA



 

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