Intensity distribution of a celestial source located at the center of the plot (blue dot) (Siegert et al. 2019). The orientation of the SPI instrument is changed in steps of two degrees to visit the locations marked on the map with black dots. The instrument remains centered on each celestial position for ≈2000s, which is called “one pointing”. The source located at the blue position is folded through the instrumental response function to determine the intensity distribution in the detector plane.