Isophotes of the 2D MoG function characterized by Eq. (3), and its main parameters for a source drifting at an angle α with respect to the X coordinate of the CCD. The speed of the source is V_u and it is observed for an interval of time T_e. The instant t = 0 corresponds to the middle of the exposure time T_e, with coordinates (x_c,y_c). The isophotes correspond to a flux level of 3 / 4F_Plateau, 1 / 2F_Plateau and 1 / 4F_Plateau, with the drifting parameter indicated by the intermediary isophote since L ≫ FWHM.