public int hilbertIndex() {
      if (commands.length < 3) {
        return 0;
      }
      int x = commands[1];
      int y = commands[2];
      return Hilbert.hilbertXYToIndex(15, x >> scale, y >> scale);
    }
Returns the hilbert index of the zig-zag-encoded first point of this feature.
<p>
This can be useful for sorting geometries to minimize encoded vector tile geometry command size since smaller
offsets take fewer bytes using protobuf varint encoding.
planetiler-core/src/main/java/com/onthegomap/planetiler/VectorTile.java