Computed ionization front around a single source in a homogeneous medium as a function of increasingly fine discretization in angles. The volume consists of 61³ grid cells and is seen pole-on (i.e., from along the z axis). Deviations from the ideal spherical shape are particularly obvious close to the planes defined by the coordinate axes in the models with a low number of rays (top row). Only with a sufficient number of rays can the models reproduce the physically expected spherical shape (bottom row).