Top left: GLIMPSE 8 μm image in our ℓ = 30° test region. Right: modified blackbody fits to the points marked on the filament in the top left panel. Since the 70 μm point is not included in these fits (see Sect. 3.2) it is plotted as an X while the other points are shown with their 20% calibration error bars. The errors quoted in temperature and column density are the formal fit errors. As discussed in Sect. 4.1, these are not necessarily representative of the true errors. Bottom left: the temperature and column densities derived along the filament, with 10 points marked. Note the inverse relation between temperature and column density in this example, especially from points 8 to 10.