Schematic illustration of the confidence curvilinear ellipsoid. Point A is the nominal position of the asteroid at time t, and point B is the VA on the main axis of the confidence ellipsoid at the same time t, which is closest to the Earth after projection onto its target plane. The arrow indicates the velocity direction of Earth with respect to the confidence ellipsoid. The bold line shows the nominal orbit of the asteroid. Image credit: Fig. 3 in Vavilov (2020).