Numerical simulation domain and example spectrum from the filament projection. Top row: axis-aligned representations of the solar filament and prominence simulation completed using MPI-AMRVAC. The cool plasma is bound by a semi-transparent density isocontour of value 1 × 10⁻¹⁴ g cm⁻³ and coloured black-red-yellow according to the local temperature, cold to hot respectively. Magnetic field lines that reveal the bounding flux rope are traced and overlaid using black, semi-transparent lines. Bottom row: comparison between the synthesis of a coronal, FAL-C model and that of a central position (0,0) Mm within the ‘Y projection’. On the right we show a sample of six lines typically used to observe filaments: Hα, Ca II 8542, Ca II H&K, and Mg II h&k.