Sketch and parametrization of the π¹ Gru A-C system. Top panel: View down onto the orbital plane. Bottom panel: System as seen from Earth on the opposite side of the z axis, with x indicating the right ascension direction, and y the declination. The X axis lies in the plane of the orbit, and is orthogonal to the node direction. The Z axis is orthogonal to the orbit plane. The orbit path above the plane of the sky (toward Earth) is shown thicker. Blue and red sections of the orbit indicate the Doppler-shift with respect to the systemic velocity of π¹ Gru A.