code: public static double[] pixelsToMeters( double px, double py, int zoom, int tileSize ) {
          double res = getResolution(zoom, tileSize);
          double mx = px * res - originShift;
          double my = py * res - originShift;
          return new double[]{mx, my};
      }
docs: Converts pixel coordinates in given zoom level of pyramid to EPSG:900913
  
  @param px       pixel x.
  @param py       pixel y.
  @param zoom     zoomlevel.
  @param tileSize tile size.
  @return converted coordinate.