np.array: The Camera's lens-shift matrix.

def _get_shift_matrix(self):
        """np.array: The Camera's lens-shift matrix."""
        return np.array([[1., 0., self.x_shift, 0.],
                         [0., 1., self.y_shift, 0.],
                         [0., 0.,           1., 0.],
                         [0., 0.,           0., 1.]], dtype=np.float32)