dot_density.sql

dot_density.sql

CREATE OR REPLACE FUNCTION cdb_dot_density(g geometry , no_points Integer, max_iter Integer DEFAULT 1000 )
   RETURNS setof geometry AS
 $$
 DECLARE  
     extent GEOMETRY;
     test_point Geometry;
     width    NUMERIC;
     height   NUMERIC;
     x0       NUMERIC;
     y0       NUMERIC;
     xp       NUMERIC;
     yp       NUMERIC;
  no_left  INTEGER;
     points   GEOMETRY[];
 BEGIN       
   extent  := ST_Envelope(g);
   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;
     
     xp = x0 + width*random();
     yp = y0 + height*random();
     test_point = CDB_LATLNG(yp,xp);
     
     IF(ST_Contains(g, test_point)) THEN
       no_left = no_left - 1;
       RETURN NEXT test_point;
     END IF;
   END LOOP;
  
  
 END
 $$
 LANGUAGE plpgsql VOLATILE