[postgis-tickets] [PostGIS] #2131: Replace regress_lots_of_points.sql data with generated query

[PostGIS]

#2131: Replace regress_lots_of_points.sql data with generated query
--------------------------+-----------------------------
  Reporter:  strk         |      Owner:  pramsey
      Type:  enhancement  |     Status:  closed
  Priority:  low          |  Milestone:  PostGIS Fund Me
 Component:  postgis      |    Version:  trunk
Resolution:  wontfix      |   Keywords:
--------------------------+-----------------------------

Comment (by Mike Toews):

 How about we make a deterministic pseudo-random point sequence, based on
 [https://en.wikipedia.org/wiki/Linear-feedback_shift_register a linear-
 feedback shift register]. This one should generate a uniform distribution
 of points between [0, 1000] in both x and y directions. And because it's
 based on a `bit(16)` postgres type, I'd expect it to be portable.
 {{{
 CREATE OR REPLACE FUNCTION
   lfsr_point(len integer, start_state integer DEFAULT 6342)
     RETURNS SETOF geometry AS
 $$
 DECLARE
   lfsr bit(16);
   bt bit(16);
   x float8;
   y float8;
 BEGIN
   lfsr := start_state::bit(16);
   FOR i IN 1..$1 LOOP
     bt := ((lfsr >> 0) # (lfsr >> 2) # (lfsr >> 3) # (lfsr >> 5)) &
 (1::bit(16));
     lfsr := (lfsr >> 1) | (bt << 15);
     x := round(lfsr::integer::numeric / 65536.0 * 1000, 4);
     bt := ((lfsr >> 0) # (lfsr >> 2) # (lfsr >> 3) # (lfsr >> 5)) &
 (1::bit(16));
     lfsr := (lfsr >> 1) | (bt << 15);
     y := round(lfsr::integer::numeric / 65536.0 * 1000, 4);
     RETURN NEXT ST_MakePoint(x, y);
   END LOOP;
   RETURN;
 END;$$ LANGUAGE plpgsql;
 }}}

 And then generate the "random" points:
 {{{
 DROP TABLE IF EXISTS test;
 CREATE TABLE test (
     "num" serial PRIMARY KEY,
     "the_geom" geometry
 );
 INSERT INTO test(the_geom)
 SELECT lfsr_point(50000);
 }}}
 This is all fine an dandy, until I looked at the points:
 https://imgur.com/FgMjyc4
 so it just needs a bit of fine tuning...

--
Ticket URL: <https://trac.osgeo.org/postgis/ticket/2131#comment:5>
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