def read_header(mat, which='def3D'):
    """Reads header for 3D data

    Parameters
    ----------
    mat : dict
        io.loadmat of the clist.mat
    which : str {'def3D', 'def'}
        which data definition to use

    Returns
    -------
    header : list of str
        list of raw observables
    """
    dd = mat[which]
    header = [dd[0, k][0] for k in range(dd.shape[1])]
    return header