Created
January 7, 2015 01:49
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A PostGIS function to create convex hulls around clusters of points
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-- USAGE | |
-- SELECT * FROM get_domains_n('poi', 'wkb_geometry', 'ogc_fid', 14000) AS g(gm geometry) | |
-- 'poi' - name of layer, 'wkb_geometry' - name of geometry column, 'ogc_fid' - primary key of table, 14000 - cluster distance. | |
CREATE OR REPLACE FUNCTION get_domains_n(lname varchar, geom varchar, gid varchar, radius numeric) | |
RETURNS SETOF record AS | |
$$ | |
DECLARE | |
lid_new integer; | |
dmn_number integer := 1; | |
outr record; | |
innr record; | |
r record; | |
BEGIN | |
DROP TABLE IF EXISTS tmp; | |
EXECUTE 'CREATE TEMPORARY TABLE tmp AS SELECT '||gid||', '||geom||' FROM '||lname; | |
ALTER TABLE tmp ADD COLUMN dmn integer; | |
ALTER TABLE tmp ADD COLUMN chk boolean DEFAULT FALSE; | |
EXECUTE 'UPDATE tmp SET dmn = '||dmn_number||', chk = FALSE WHERE '||gid||' = (SELECT MIN('||gid||') FROM tmp)'; | |
LOOP | |
LOOP | |
FOR outr IN EXECUTE 'SELECT '||gid||' AS gid, '||geom||' AS geom FROM tmp WHERE dmn = '||dmn_number||' AND NOT chk' LOOP | |
FOR innr IN EXECUTE 'SELECT '||gid||' AS gid, '||geom||' AS geom FROM tmp WHERE dmn IS NULL' LOOP | |
IF ST_DWithin(ST_Transform(ST_SetSRID(outr.geom, 4326), 3785), ST_Transform(ST_SetSRID(innr.geom, 4326), 3785), radius) THEN | |
--IF ST_DWithin(outr.geom, innr.geom, radius) THEN | |
EXECUTE 'UPDATE tmp SET dmn = '||dmn_number||', chk = FALSE WHERE '||gid||' = '||innr.gid; | |
END IF; | |
END LOOP; | |
EXECUTE 'UPDATE tmp SET chk = TRUE WHERE '||gid||' = '||outr.gid; | |
END LOOP; | |
SELECT INTO r dmn FROM tmp WHERE dmn = dmn_number AND NOT chk LIMIT 1; | |
EXIT WHEN NOT FOUND; | |
END LOOP; | |
SELECT INTO r dmn FROM tmp WHERE dmn IS NULL LIMIT 1; | |
IF FOUND THEN | |
dmn_number := dmn_number + 1; | |
EXECUTE 'UPDATE tmp SET dmn = '||dmn_number||', chk = FALSE WHERE '||gid||' = (SELECT MIN('||gid||') FROM tmp WHERE dmn IS NULL LIMIT 1)'; | |
ELSE | |
EXIT; | |
END IF; | |
END LOOP; | |
RETURN QUERY EXECUTE 'SELECT ST_ConvexHull(ST_Collect('||geom||')) FROM tmp GROUP by dmn'; | |
RETURN; | |
END | |
$$ | |
LANGUAGE plpgsql; | |
-- Credit to drnextgis: http://gis.stackexchange.com/a/11807/10198 |
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