code: def obj_assd(result, reference, voxelspacing=None, connectivity=1):
      
      assd = numpy.mean( (obj_asd(result, reference, voxelspacing, connectivity), obj_asd(reference, result, voxelspacing, connectivity)) )
      return assd
docs: Average symmetric surface distance.
      
      Computes the average symmetric surface distance (ASSD) between the binary objects in
      two images.
      
      Parameters
      ----------
      result : array_like
          Input data containing objects. Can be any type but will be converted
          into binary: background where 0, object everywhere else.
      reference : array_like
          Input data containing objects. Can be any type but will be converted
          into binary: background where 0, object everywhere else.
      voxelspacing : float or sequence of floats, optional
          The voxelspacing in a distance unit i.e. spacing of elements
          along each dimension. If a sequence, must be of length equal to
          the input rank; if a single number, this is used for all axes. If
          not specified, a grid spacing of unity is implied.
      connectivity : int
          The neighbourhood/connectivity considered when determining what accounts
          for a distinct binary object as well as when determining the surface
          of the binary objects. This value is passed to
          `scipy.ndimage.morphology.generate_binary_structure` and should usually be :math:`> 1`.
          The decision on the connectivity is important, as it can influence the results
          strongly. If in doubt, leave it as it is.
          
      Returns
      -------
      assd : float
          The average symmetric surface distance between all mutually existing distinct
          binary object(s) in ``result`` and ``reference``. The distance unit is the same as for
          the spacing of elements along each dimension, which is usually given in mm.
          
      See also
      --------
      :func:`obj_asd`
      
      Notes
      -----
      This is a real metric, obtained by calling and averaging
      
      >>> obj_asd(result, reference)
      
      and
      
      >>> obj_asd(reference, result)
      
      The binary images can therefore be supplied in any order.