No data reduction package has all the functionalities any user dream about. But a user may know that the functionality he needs is available in a very specific package. Here comes the need to exchange data between packages. The current standard answer to this problem is FITS. CLASS to FITS conversion (and vice-versa) is done by command FITS. In addition, all functionalities provided by the SIC command DEFINE FITS are of course available. For a description of the FITS format see the original paper by Wells et al. (Astron. and Astrophys. Suppl.).
The CLASS FITS command has the following syntax:
FITS READ Filename[.fits]to read a FITS file and create CLASS data from it, or
FITS WRITE Filename[.fits] [/BITS Nbits] [/MODE SPECTRUM|INDEX]to write a FITS file from CLASS data.
In addition, default values can be supplied by the SET FITS command.
SET FITS BITS Nbits
SET FITS MODE Spectrum|Index|None