Create DCM (Matrix3) from q
        :param q: array q which represents a quaternion [w, x, y, z]
        :returns: Matrix3

def _q_to_dcm(self, q):
        """
        Create DCM (Matrix3) from q
        :param q: array q which represents a quaternion [w, x, y, z]
        :returns: Matrix3
        """
        assert(len(q) == 4)
        arr = super(Quaternion, self)._q_to_dcm(q)
        return self._dcm_array_to_matrix3(arr)