Computing Hulls from a List of Geometries

hulls.sql

-- Compute Convex Hull for a list of geolocations matching the outcode 'SW1A'
SELECT 
	ST_AsText(ST_ConvexHull(ST_Collect(location::geometry))) AS hull
FROM 
	postcodes
WHERE
	outcode = 'SW1A';

-- Compute Concave Hull for a list of geolocations matching the outcode 'SW1A'
-- Little bit more expensive but the polygons are a "tighter fit", the more you increase the second parameter the "tightness" increases but so does computational work required
SELECT 
	ST_AsText(ST_ConcaveHull(ST_Collect(location::geometry), 0.99)) AS hull
FROM 
	postcodes
WHERE
	outcode = 'AB10';


-- Create a table of outcode and associated convex hulls
CREATE TABLE outcode_hulls 
AS SELECT 
	outcode, 
	ST_ConvexHull(ST_Collect(location::geometry)) AS convex_hull
FROM
	postcodes
GROUP BY
	postcodes.outcode;