airmass will probably be a function, but if folks think a value is better (e.g. if some project does a fancy computation instead of the usual altitude->airmass) then it will be a value and we will provide the usual function, so that obs_ packages can easily compute it when raw data is loaded
How are you thinking of doing this? The true airmass depends on atmospheric pressure and temperature (an approximation to the pressure scale height). You were going to assume a scale height and a plane-parallel atmosphere?
I worry about blessing something that we know is wrong; assuming a canonical atmosphere and doing the geometry right might be an option (maybe with optional arguments).
camera will be added to Detector as cameraName
Does this allow a user to lookup the camera given the name? In python (and given a butler) you can ask for the camera; are we providing a way to do this in C++? Or is this cameraName just for jointcal's sake before we get a chance to fix the code to not need to know its camera?
I'm worried about the comments about the Wcs. For now that's fine, but with the new design will the same problem be present, or will the code know its limitations? How can we calculate the boresight position ourselves if all we have is a Wcs and Detector?