code: public static double[] tileBounds3857( int tx, int ty, int zoom, int tileSize ) {
          double[] min = pixelsToMeters(tx * tileSize, ty * tileSize, zoom, tileSize);
          double minx = min[0], miny = min[1];
          double[] max = pixelsToMeters((tx + 1) * tileSize, (ty + 1) * tileSize, zoom, tileSize);
          double maxx = max[0], maxy = max[1];
          return new double[]{minx, miny, maxx, maxy};
      }
docs: Returns bounds of the given tile in EPSG:3857 coordinates
  
  @param tx       tile x.
  @param ty       tile y.
  @param zoom     zoomlevel.
  @param tileSize tile size.
  @return [minx, miny, maxx, maxy]