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rochoa/dot_density.sql

Forked from stuartlynn/dot_density.sql
Last active February 14, 2017 16:58
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dot_density.sql
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dot_density.sql
-- Source code from https://github.com/CartoDB/crankshaft/blob/develop/src/pg/sql/30_dot_density.sql
CREATE OR REPLACE FUNCTION cdb_dot_density(geom geometry , no_points Integer, max_iter_per_point Integer DEFAULT 1000)
RETURNS GEOMETRY AS $$
DECLARE
extent GEOMETRY;
test_point Geometry;
width NUMERIC;
height NUMERIC;
x0 NUMERIC;
y0 NUMERIC;
xp NUMERIC;
yp NUMERIC;
no_left INTEGER;
remaining_iterations INTEGER;
points GEOMETRY[];
bbox_line GEOMETRY;
intersection_line GEOMETRY;
BEGIN
extent := ST_Envelope(geom);
width := ST_XMax(extent) - ST_XMIN(extent);
height := ST_YMax(extent) - ST_YMIN(extent);
x0 := ST_XMin(extent);
y0 := ST_YMin(extent);
no_left := no_points;
LOOP
if(no_left=0) THEN
EXIT;
END IF;
yp = y0 + height*random();
bbox_line = ST_MakeLine(
ST_SetSRID(ST_MakePoint(yp, x0),4326),
ST_SetSRID(ST_MakePoint(yp, x0+width),4326)
);
intersection_line = ST_Intersection(bbox_line,geom);
test_point = ST_LineInterpolatePoint(st_makeline(st_linemerge(intersection_line)),random());
points := points || test_point;
no_left = no_left - 1 ;
END LOOP;
RETURN ST_Collect(points);
END;
$$
LANGUAGE plpgsql VOLATILE;
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