def to_transformation_matrix(self):
    """ Return the [4x4] transformation matrix (zero translation). """
    transformation_matrix = np.identity(4)
    transformation_matrix[0:3, 0:3] = self.to_rotation_matrix()
    return transformation_matrix.copy()
 Return the [4x4] transformation matrix (zero translation). 
hand_eye_calibration/python/hand_eye_calibration/quaternion.py