def _plot_dig_transformation(transformed, original, title=''):
    EXPECTED_HEAD_SIZE = 0.085
    from mne.viz.backends.renderer import _Renderer
    def get_data(montage):
        data, coord_frame = _get_fid_coords(montage.dig)
        data['eeg'] = np.array([ch['r'] for ch in _get_dig_eeg(montage.dig)])
        data['coord_frame'] = coord_frame

        return data

    def _plot_fid_coord(renderer, data, color):
        renderer.tube(
            # origin=data.lpa,  # XXX: why I cannot pas a (3,) ?
            origin=np.atleast_2d(data.lpa),
            destination=np.atleast_2d(data.rpa),
            # color='red',  # XXX: why I cannot do that?
            color=color,
            radius=0.001,  # XXX: why radious=1 which is default does not work?
        )
        renderer.tube(
            origin=np.atleast_2d((data.lpa+data.rpa)/2),
            destination=np.atleast_2d(data.nasion),
            color=color,
            radius=0.001,  # XXX: why radious=1 which is default does not work?
        )

    ren = _Renderer()
    ren.sphere(
        center=np.array([0, 0, 0]),
        # color=(100, 100, 100),  # XXX: is color (R,G,B) 0-255? doc needs rev.
        color=(1.0, 1.0, 1.0),  # XXX: doc don't say [0-1 or 0-255] ??
        # scale=EXPECTED_HEAD_SIZE,  # XXX: why I cannot put radius a value in mm??  # noqa
        scale=0.17,  # XXXX magic number!!
        opacity=0.3,
        resolution=20,  # XXX: why this is not callen n_poligons??
        backface_culling=False,
    )
    N_RAND_PTS = 50
    ren.sphere(
        center=_sph_to_cart(np.stack(
            [np.full((N_RAND_PTS,), EXPECTED_HEAD_SIZE),
             np.random.rand(N_RAND_PTS) * 3 * 3.1415,
             np.random.rand(N_RAND_PTS) * 3 * 3.1415,
            ],
            axis=-1,
        )),
        color=(1.0, 1.0, 1.0),
        scale=0.001
    )

    orig_data = get_data(original)
    trans_data = get_data(transformed)

    for oo, tt in zip(orig_data.eeg, trans_data.eeg):
        ren.tube(
            origin=np.atleast_2d(oo),
            destination=np.atleast_2d(tt),
            color=(.0, .1, .0),
            radius=0.0005,
        )

    _plot_fid_coord(ren, orig_data, (1.0, 0, 0))
    ren.sphere(center=orig_data.eeg, color=(1.0, .0, .0), scale=0.0022)

    _plot_fid_coord(ren, trans_data, (0, 0, 1.0))
    ren.sphere(center=trans_data.eeg, color=(.0, .0, 1.0), scale=0.0022)


    ren.text2d(
        x=0, y=0,  # XXX: why not x_window, y_window (to me x, y feels weird. They seem to belong to the scene x,y)
        text=title,
        width=.1  # XXX: This is relative to the displaying window. caThoughts on n we just pas something that is independent of wind.size
    )
    ren.show()

    return