code: public double[] tile2Bounds( final int tx, final int ty, final int zoom ) {
          double[] nswe = new double[4];
          nswe[0] = tile2lat(ty, zoom);
          nswe[1] = tile2lat(ty + 1, zoom);
          nswe[2] = tile2lon(tx, zoom);
          nswe[3] = tile2lon(tx + 1, zoom);
          return nswe;
      }
docs: Convert a tile coordinate at a given zoom to its lat/lon bounds.
  
  @param tx tile x.
  @param ty tile y.
  @param zoom the zoom level.
  @return the bounds as [n,s,w,e].