Jake - thanks - there are ways to do this, just go ahead.
Asher, I did not try other projections. The inverted U is a good and healthy idea. The cloud was there, no PP involved.
Tom Dinning - thanks, yes, the projection on the ceiling is a good idea.
Tom Robbins - thanks - I have to admit that I was lazy and used the built-in panorama function. The focal length was 7.1mm, which is a 28mm FoV equivalent for 36x24mm sensor/negative. I do not know the number of frames, but the overlap for the in-camera creation of panoramas is quite large, so 15 or more frames can be involved here. The resolution is only 1920x1200 per frame in this case.
Best regards,
Michael