anchor.diff:  %% --------------------------------------------------------------------
   is_pos_code(<<Depth:8,
                 _PathCode:(3*?DEFAULT_MAX_DEPTH)/bits,
  -              _Padding:((8-((3*?DEFAULT_MAX_DEPTH) rem 8)) rem 8)/bits>>) 
  -  when Depth >= ?DEFAULT_MAX_DEPTH -> false; 
  +              _Padding:((8-((3*?DEFAULT_MAX_DEPTH) rem 8)) rem 8)/bits>>)
  +  when Depth >= ?DEFAULT_MAX_DEPTH -> false;
   
  -is_pos_code(<<_Depth:8, 
  +is_pos_code(<<_Depth:8,
                 _PathCode:(3*?DEFAULT_MAX_DEPTH)/bits,
                 _Padding:((8-((3*?DEFAULT_MAX_DEPTH) rem 8)) rem 8)/bits>>)  -> true;
   
  
positive.code: %% <p>DEFAULT_MAX_DEPTH currently is fixed at 60, allowing the smallest
  %% node of the octree to be 2^60 ~= 10^24 times smaller than the space
  %% encompassed by the whole tree.</p>
  %%  
  %% <p>The values for each coordinate c of the position and size are assumed to 
  %% be normalized to be within the interval ( 0.0 <= c < 1.0 )</p>
  %% @end
  
  
negative.code: %% @end
  -spec to_pos_code(#ot_node_id{}) -> pos_code().
  %% --------------------------------------------------------------------
  to_pos_code(NId) -> to_pos_code(NId, ?DEFAULT_MAX_DEPTH).
  
  %% to_pos_code/2
  %% --------------------------------------------------------------------
  %% @doc create pos code from node specification.
  %%
  %% @end
  -spec to_pos_code(#ot_node_id{}, MaxDepth :: pos_integer()) -> pos_code().
  %% --------------------------------------------------------------------
  to_pos_code(NId, MaxDepth) ->
      Spec = quperl_octree:to_node_list(NId),
  
      {Depth, PosCode} = lists:foldl(fun add_pos_code/2, {0,<<>>}, Spec),
  
      <<Depth,
        PosCode/bits, 0:((MaxDepth-Depth)*3),
        0:((8-((3*MaxDepth) rem 8)) rem 8)>>.
  
  
  
  