Core 4 modelled with anisotropic radiation field. Frames a) and b) are the 160 μm and 500 μm surface brightness maps from Cloud II (the “observations”). The core is visible in the map of the true column density (frame c) but is missed by the constructed model (frame d). Frames e) and f) show the errors of the model predictions S_Model relative to the observed surface brightness S_Obs at the wavelengths of 160 μm and 500 μm, respectively.