Aitoff projection

GILDAS implements the AIT projection only for $\delta _0 = 0$; non-zero reference declinations are always ignored when projecting or unprojecting positions, even if the data format usually saves any declination value. This implementation is compatible⁷ with the AIPS (and thus the CG02) convention in the $\delta _0 = 0$ case.

Note, however, that when data were exported to FITS files, GILDAS versions earlier than aug23 were using the possibly non-zero declinations as the CRVAL2 value. This is incorrect and was leading to wrong interpretation of the maps by third-party software. This is fixed in the aug23 release by always setting CRVAL2 parameter to 0 for the AIT projection.

If, at some point, the non-zero declination case is to be implemented in GILDAS, we should choose the newest formalism, i.e. the CG02 one⁸