<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def transformation_matrix(self):
 """Get the 4x4 homogeneous transformation matrix equivalent of the quaternion rotation. Returns: A 4x4 homogeneous transformation matrix as a 4x4 Numpy array Note: This feature only makes sense when referring to a unit quaternion. Calling this method will implicitly normalise the Quaternion object to a unit quaternion if it is not already one. """

        t = np.array([[0.0], [0.0], [0.0]])
        Rt = np.hstack([self.rotation_matrix, t])
        return np.vstack([Rt, np.array([0.0, 0.0, 0.0, 1.0])])