Results for the ellipsoid model. The frames a)–c) show the true column densities towards three directions. The errors in the column density estimates of Method B and of the 3D modelling are shown in frames d)–f) and g)–i), respectively, with contours drawn at − 3    ×    10²¹cm^-2 and − 6 × 10²¹cm^-2. The bottom frames show the radial column density profiles. The true column density is shown with a black solid line, the grey area indicating the 1σ variation in the averaged rings. The triangles correspond to Method B and the square symbols to the 3D modelling. The error bars indicate the corresponding 1σ variation in the averaged rings.