Solar wind ballistic propagation method. d₀ is the solar distance of the speed map, v is the solar wind speed. The radial distance of the propagated solar wind (d_n, where n is the number of the propagation step) is calculated based on the radial speed of the solar wind, while it is shifted in longitude according to the synodic solar rotation. t_step = T/N is the duration of one propagation step, where T is the synodic rotation period of the solar corona, and N is the number of datapoints of the input data in one heliographic latitude, over one Carrington rotation.