a plsql function to get a PostGIS geom out of a tile defined by X,Y,Z. Returns on SRS 900913

v_get_tile.plsql

CREATE OR REPLACE FUNCTION v_get_tile(x integer,y integer,z integer) 
  RETURNS geometry AS
$BODY$
DECLARE
  origin_shift CONSTANT FLOAT := 20037508.342789244;
  initial_resolution CONSTANT FLOAT := 156543.03392804062;
  res float;
  minx float; 
  miny float; 
  maxx float; 
  maxy float;
BEGIN
  res  := initial_resolution / (power(2,z));

  minx := (x*256)*res  - origin_shift;
  miny := -((y*256)*res  - origin_shift);
  maxx := ((x+1)*256)*res  - origin_shift;
  maxy := -(((y+1)*256)*res  - origin_shift);  
  

RETURN (ST_GeomFromText('POLYGON(('||minx||' '||maxy||','||maxx||' '||maxy||','||maxx||' '||miny||','||minx||' '||miny||','||minx||' '||maxy||'))',900913));END;
$BODY$
  LANGUAGE 'plpgsql' IMMUTABLE STRICT
  COST 100;

Shouldn't resolution be 4^Z rather than 2^Z ?
Another thought is that the use of floating point numbers may make it so that adjacent tiles aren't really touching (by very small amount).
I'll give that a try, and grid if needed.

I was clearly wrong, resolution is 2^Z (number of tiles would be 4^Z)

thanks! I did all this in a hurry... Javier de la Torre @jatorre Vizzuality 148 Lafayette St. PH, New York, 10013,USA +1 347 320 7715 www.vizzuality.com

…

On Apr 26, 2012, at 7:17 AM, strk wrote: I was clearly wrong, resolution is 2^Z (number of tiles would be 4^Z) --- Reply to this email directly or view it on GitHub: https://gist.github.com/734018