Emerging SEDs of RADMC-3D (solid black lines) and of the DGFEM code, computed from the post-processing ray-tracing procedure (orange dots), and from the DGFEM solution at the outer edge (blue crosses). The left panel corresponds to the optically thick spherically symmetric case (τ = 100, see Sect. 5.1) while the right panel corresponds to the optically thick disc benchmark from Sect. 5.2. The lower panels show the relative difference between the curves of this study and the benchmarks.