Isometric projection of the best-fit infalling trajectory for streamers around S CrA (left panel) and HL Tau (right panel), in 3D position– position-position space (RA, Dec, and LOS or radial distance). The black line represents the analytical trajectory from our implementation of the Mendoza et al. (2009) models, as described in Sect. 2.1. Blue spheres represent solutions from two-body REBOUND simulations (Rein & Liu 2012). The red diamonds denote the position of the center of mass of the protostellar systems. The purple circles denote the initial position of the infalling gas. These trajectories are computed up to the closest approach of infalling material to the protostellar system.