Two steps in the definition of SMOK coordinates. In the top diagram the motion of an object in the vicinity of the fixed point c is modelled by the function b(t) expressed in the barycentric [ xyz ] system. A scaled version of the model is constructed such that the scaled c is at unit distance from the solar system barycentre (SSB). In the bottom diagram new coordinate axes [ p_cq_cr_c ] are chosen in the directions of increasing right ascension, declination, and distance, respectively, at the comparison point (α_c,δ_c) being the projection of c on the unit sphere.