Diagram of the model. We take into account the four observers per declination angle at a distance of 10 pc in the planes defined by the directions of opposition (O), western quadrature (WQ), conjunction (C), and eastern quadrature (EQ), and the rotational axis. The intersection of the direction vectors (red) with the sphere of 10 pc (blue) define their position. The sub-observer point is defined by the intersection with the planetary surface (black).