code: public static long encodePolyId(int salt, int it, int ip) {
          return (((long) salt) << (DT_POLY_BITS + DT_TILE_BITS)) | ((long) it << DT_POLY_BITS) | ip;
      }
docs: Derives a standard polygon reference.
  
  @note This function is generally meant for internal use only.
  @param salt
  The tile's salt value.
  @param it
  The index of the tile.
  @param ip
  The index of the polygon within the tile.
  @return encoded polygon reference