Since version 3.1 of A User's Guide for the Flexible Image Transport System
(FITS) was published, there have been several significant developments in
the FITS community:
The International Astronomical Union FITS Working Group (IAUFWG) has endorsed
the image (IMAGE) and binary table (BINTABLE) extensions
and the agreement on physical blocking.
The proposal for treatment of world coordinate systems has been
expanded and refined.
A number of conventions that are not part of the formal FITS rules
have come into wide use.
A significant body of FITS resources has become available on the
World Wide Web.
This new version of the User's Guide has been written to reflect those
changes. The discussion of the image extension and the rules for the binary table
extension have been moved from section 5 (Advanced FITS)
to section 3 (FITS Fundamentals)
. The papers describing the image and binary table extensions have now been published
in the Astronomy and Astrophysics Supplement Series and are now considered
to be among the fundamental FITS papers. Section 4
on World Coordinates has been updated to include the refinements incorporated
in the current proposals, and it also discusses in greater detail how widely the
different proposed conventions are used in the general community. The discussion
of the three proposed binary table conventions, which are not part of the formal
structure endorsed by the IAUFWG, remains in section 5.
The discussion of applications of binary tables has been significantly expanded,
and descriptions of a number of binary table and other conventions have been added.
Section 6 has been rewritten
to emphasize network sources of FITS information, and it discusses a number of
sites on the World Wide Web that contain FITS documents, software, and sample
files. Many of these sites did not exist when version 3.1 of the User's Guide
was written, and others have been greatly expanded since. Three additional sample
FITS headers, one using an ASCII table and two using binary tables, have been
added to Appendix A. Appendix
B lists the IEEE floating point number type corresponding
to every bit pattern. Thanks for comments on an earlier draft of version 4 go
to M.Calabretta, D.Jennings, W.Pence, and R.Thompson. Also, thanks to D.Leisawitz
for providing the DIRBE FITS header (example 6) and W.Pence for providing the
ASCA FITS header (example 7). To be of most use to readers, a guide such as this
one must go beyond the formal rules to discuss common practices that are not specified
by those rules. In addition, users who are designing and developing FITS files
need to know how FITS is likely to develop. Developing a formal standard for FITS
has clarified a number of points that had been unclear or ambiguous in the original
FITS papers. Some of the issues were regarded as not appropriate for a formal
standard but deserving of further detailed discussion; at the recommendation of
the Technical Panel developing the NASA/Science Office of Standards and Technology
(NOST) standard, they are included in this Guide. Queries to the FITS
Support Office and discussion on the FITS network newsgroup sci.astro.fits
and the associated fitsbitselectronic mail exploder have identified
other points in need of explanation. This Guide also describes a number
of conventions that are widely used but have not been formally adopted by the
FITS governing structure under the IAUFWG. Description in this Guide
of such conventions is intended neither as a NASA endorsement nor as a requirement
for use of these conventions by NASA projects. Where an issue is controversial,
this Guide attempts to provide the arguments on all sides. FITS is continually
expanding: new conventions are proposed, existing proposals are modified, new
issues are raised; and the FITS committees act. Some of this progress will occur
during the period this Guide is being proofed and undergoing physical composition.
Thus, some of these developments may, unfortunately, not make it into the current
User's Guide. To keep up with current events, use the resources described
in Section 6. Similarly, Web sites may be reorganized
and the URLs corresponding to an individual page may change. In that case, the
new location can generally be found by going to the main page for the site and
following appropriate links. As always, comments about the Guide, in
particular about areas that need clarification or expansion, are encouraged. Send
questions or comments to
