55 lines
1.7 KiB
PL/PgSQL
55 lines
1.7 KiB
PL/PgSQL
--
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-- Creates N points randomly distributed arround the polygon
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--
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-- @param g - the geometry to be turned in to points
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--
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-- @param no_points - the number of points to generate
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--
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-- @params max_iter_per_point - the function generates points in the polygon's bounding box
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-- and discards points which don't lie in the polygon. max_iter_per_point specifies how many
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-- misses per point the funciton accepts before giving up.
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--
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-- Returns: Multipoint with the requested points
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CREATE OR REPLACE FUNCTION cdb_dot_density(geom geometry , no_points Integer, max_iter_per_point Integer DEFAULT 1000)
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RETURNS GEOMETRY AS $$
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DECLARE
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extent GEOMETRY;
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test_point Geometry;
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width NUMERIC;
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height NUMERIC;
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x0 NUMERIC;
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y0 NUMERIC;
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xp NUMERIC;
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yp NUMERIC;
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no_left INTEGER;
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remaining_iterations INTEGER;
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points GEOMETRY[];
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bbox_line GEOMETRY;
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intersection_line GEOMETRY;
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BEGIN
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extent := ST_Envelope(geom);
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width := ST_XMax(extent) - ST_XMIN(extent);
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height := ST_YMax(extent) - ST_YMIN(extent);
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x0 := ST_XMin(extent);
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y0 := ST_YMin(extent);
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no_left := no_points;
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LOOP
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if(no_left=0) THEN
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EXIT;
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END IF;
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yp = y0 + height*random();
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bbox_line = ST_MakeLine(
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ST_SetSRID(ST_MakePoint(yp, x0),4326),
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ST_SetSRID(ST_MakePoint(yp, x0+width),4326)
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);
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intersection_line = ST_Intersection(bbox_line,geom);
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test_point = ST_LineInterpolatePoint(st_makeline(st_linemerge(intersection_line)),random());
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points := points || test_point;
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no_left = no_left - 1 ;
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END LOOP;
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RETURN ST_Collect(points);
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END;
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$$
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LANGUAGE plpgsql VOLATILE
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