Computation of high-resolution single line profiles with PRODIMO (black lines) and FLITS (red lines) based on a medium-resolution 90×70 disc model. Left panel: o-H₂O rotational line 13_6,5 → 12_4,9 at 12.453 μm with an excitation energy of 4213 K, which is emitted partly from the inner rim of the disc, and partly from the disc surface up to a radius of about 0.4 au in this model. Right panel: o-H₂ O rotational line 8_5,4 → 8_2,7 at 27.059 μm is depicted, which has an excitation energy of 1806 K and is mainly emitted from the disc surface up to a radius of about 1 au. The time consumption is about 92 CPU-sec with PRODIMO (251 velocity-channels, 356 × 144 rays) and 1.2 CPU-sec with FLITS with enhanced accuracy settings (173 channels, 22375 rays), i.e. enhanced over FLITS standards.