public Envelope getEnvelope() {
    double worldWidthAtZoom = Math.pow(2, z);
    return new Envelope(
      GeoUtils.getWorldLon(x / worldWidthAtZoom),
      GeoUtils.getWorldLon((x + 1) / worldWidthAtZoom),
      GeoUtils.getWorldLat((y + 1) / worldWidthAtZoom),
      GeoUtils.getWorldLat(y / worldWidthAtZoom)
    );
  }
Returns the latitude/longitude of the northwest corner of this tile.
planetiler-core/src/main/java/com/onthegomap/planetiler/geo/TileCoord.java