Distortion for METIS (draft)

[oczoske]

Spatial (angular) distortions are deperately needed, most urgently for METIS AIT activities using the WCU. The idea currently is to restrict the implementation to scenes that only have point sources and are instantiated via tables with positions. This covers in particular the METIS grid masks, but also star fields. Image and cube sources are much harder but there are actually not many use cases for those that also require distortions to be taken into account.
More details to follow