Stellar kinematic measurements. Top: Voronoi binned mean velocity fields for an example TNG100 galaxy, with a central bulge and a relatively massive disk. For this galaxy the random LOS projection almost coincides with the edge-on projection. The projected major axis is aligned with the X axis. The data points show the projected (X, Y) positions of the stellar particles, and are colored according to the mean velocity and velocity dispersion of the corresponding Voronoi bin as shown by the colorbars. Center: smoothed velocity and velocity dispersion fields for the same example galaxy above. The central disk structure is embedded in a spheroidal stellar halo. Bottom: kinematic parameters of the galaxy shown above, derived from the Voronoi binned velocity fields (orange open circles) and from the smoothed velocity fields (blue points).