generate_random_location

gistfile1.txt

create or replace function generate_random_location(p_island in sdo_geometry)
  return sdo_geometry
is
  v_center sdo_geometry;
  v_radius number;
  new_radian number;
  new_point sdo_geometry;
  v_lon number;
  v_lat number;
  v_x number;
  v_y number;
  new_line sdo_geometry;
  final_point sdo_geometry;
  v_length number;
begin
  v_center := sdo_geom.sdo_mbc_center(p_island, 0.005);
  v_radius := sdo_geom.sdo_mbc_radius(p_island, 0.005) * 1.1; --add a little to make sure it's outside
  
  /* get the island center's x y */
  select t.x, t.y into v_lon, v_lat
    from table(sdo_util.getvertices(v_center)) t;

  /* random radian from 0 to 2pi */
  new_radian := dbms_random.value(0,asin(1)*4);
    
  /* generate a point on the new radian outside of the polygon */
  new_point := sdo_util.point_at_bearing(
                         sdo_geometry(2001,
                                      4326,
                                      sdo_point_type(v_lon, v_lat, null), null, null),
                   new_radian,
                   v_radius
               );

  /* get the new point's x y */
  select t.x, t.y into v_x, v_y
    from table(sdo_util.getvertices(new_point)) t;
              
  /* create a line from the center to the new point
     get the segment that is contained inside the polygon
  */
  new_line := sdo_geom.sdo_intersection(
                       sdo_geometry (2002, 4326, null,
                                     sdo_elem_info_array (1,2,1),
                                     sdo_ordinate_array (v_lon, v_lat,v_x, v_y)
                                    ),
                       p_island,
                       0.005
              );
    
  /* get the length of the new line */
  v_length := round(sdo_geom.sdo_length(new_line, 0.05));

  /*
    using the length of the new line,
    generate a point on the current radian with a random distance from 0 to the lenght of the line
  */
  final_point := sdo_util.point_at_bearing(
                   sdo_geometry(2001, 4326,
                                sdo_point_type(v_lon, v_lat, null), null, null),
                   new_radian,
                   dbms_random.value(0,v_length)
                 );

  return final_point;
end;