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FITS for crystallography ?


I agree with Marty, that FITS is well worth looking at. It shows that
the Astronomy community has already adopted a similar solution to the
one which we have been discussing. It's also interesting to see some of
the history and development of the format. 

A lot of good work has gone into the document. I particularly like
the "Onces FITS, always FITS" philosophy. This sums up very neatly, 
something which I only managed to say very clumsily.

However, a few differences and limitations need to be born in mind:

1. Keywords (data names) are a maximum of 8 characters in length.
   (Fitting CIF data names into 8 characters would be challenging !
   How human readable would 8 character data names be ?)

2. Unsigned 16-bit integer data type does not exist. (A method to
   convert such data into signed 16-bit integers and the reverse is
   described using the BZERO and BSCALE keywords, but this seems strange.
   Astronomers need 16 bit unsigned integers as much as we do.)

3. Data compression doesn't exist. (A proposal was made back in
   1990/1991 to extend the format to support various forms of
   data compression. A very similar scheme to my 'byte_offsets'
   scheme is proposed as "Previous pixel compression". However,
   since 1991 this seems to have kept it's status as a proposal.)

(4. Other differences exist which may upset some people. e.g. It's a much
    more "fixed format" FORTRAN-77 type header.)

Perhaps the second and thirds point illustrate a much more important 
question. Brian suggests that a general shared format could be a good 
idea. Theoretically this seems a worthy aim, but how practical would 
this situation be ? e.g. How would the IUCr and IAU (International 
Astronomy Union, which maintains FITS) coordinate development ? Would 
the development pace be appropriate for both communities ?

These are not questions which I can answer. Perhaps COMCIFS / IUCr
should consider the implications of such an approach. 

    Andy

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