Radio projection

The GILDAS kernel implements the so-called radio projection with the same formalism as AIPS GLS (Eqs. 1 and 2). In particular, this projection system is used natively at the IRAM-30m telescope and is preserved to describe the position of pointed spectra, or on-the-fly observations and the resulting reconstructed position-position-velocity cubes. Up to GILDAS version jul23, the radio-projection description was exported under the -GLS suffix in FITS header files (GILDAS command V $\backslash$FITS output.fits FROM input.gdf).

However, it appeared that this could cause issues when the exported FITS are interpreted by some third-party software. Many FITS-based software implement an implicit GLS-to-SFL conversion as suggested by CG02. However, some seem to implement it incorrectly (the translation is not correctly applied), while some other just fail in this case (CASA, CARTA). Because of these various troubles, it is decided not to export any more FITS data out of GILDAS with the radio/GLS description.