Angle between reference_point and self[monomer_index][res_label].

        Notes
        -----
        Angle is calculated using the dihedral angle, with the 
        second and third points coming from the curve_primitive.

        Parameters
        ----------
        reference_point : list, tuple or numpy.array of length 3.
        monomer_index : int
            Index of the Residue to centre.
        res_label : str
            Atom name for centred atom, e.g. "CA" or "OE1".
        radians : bool
            If True, then desired_angle is in radians instead of degrees.

def get_orient_angle(self, reference_point=numpy.array([0, 0, 0]),
                         monomer_index=0, res_label='CA', radians=False):
        """ Angle between reference_point and self[monomer_index][res_label].

        Notes
        -----
        Angle is calculated using the dihedral angle, with the 
        second and third points coming from the curve_primitive.

        Parameters
        ----------
        reference_point : list, tuple or numpy.array of length 3.
        monomer_index : int
            Index of the Residue to centre.
        res_label : str
            Atom name for centred atom, e.g. "CA" or "OE1".
        radians : bool
            If True, then desired_angle is in radians instead of degrees.
        """
        if (monomer_index < len(self)) and monomer_index != -1:
            adjacent_index = monomer_index + 1
        elif (monomer_index == len(self)) or monomer_index == -1:
            adjacent_index = monomer_index - 1
        else:
            raise ValueError(
                "centred_index ({0}) cannot be greater than the "
                "length of the polymer ({1})".format(
                    monomer_index, len(self)))
        angle = dihedral(reference_point,
                         self.curve_primitive[monomer_index]['CA'],
                         self.curve_primitive[adjacent_index]['CA'],
                         self[monomer_index][res_label])
        if radians:
            angle = numpy.deg2rad(angle)
        return angle