[fitsbits] Start of Public Comment Period on FITS Binary Table Proposals

William Pence William.D.Pence at nasa.gov
Thu Oct 14 12:56:40 EDT 2004


ANNOUNCEMENT:  START OF FORMAL PUBLIC COMMENT PERIOD


This is to announce the official start of the 4-week formal Public Comment
Period on 2 proposals concerning conventions used within FITS binary tables.
These conventions are currently defined in the unofficial Appendix B of the
FITS Standard document.  The purpose of the current 2 proposals is to
officially approve these conventions and to incorporate them into the FITS
Standard.

The 2 proposals are attached to this message below for your review and
comment.  The full text of Appendix B of the NOST FITS Standard (on page 57
of the printed document) may be viewed in HTML, PDF, or Postscript formats at:

http://archive.stsci.edu/fits/fits_standard/
ftp://legacy.gsfc.nasa.gov/fits_info/fits_office/fits_standard.pdf
ftp://legacy.gsfc.nasa.gov/fits_info/fits_office/fits_standard.ps.gz

Note that only sections B.1 and B.2 of the appendix are covered by these
proposals.  Appendix B.3 is not being considered for approval at this time.

Please review these proposals carefully and post any comments, criticisms,
or suggestions here on the sci.astro.fits newsgroup, or on the related
FITSBITS moderated mail list.  (You can subscribe to FITSBITS at
http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits).

Under the "Rules and Procedures" of the IAU FITS Working Group, the first
step in the official approval process of any FITS proposal is a formal
Public Comment Period to take place on the sci.astro.fits newsgroup
and the moderated FITSBITS mail list.  At the end of this public comment
period the regional FITS committees (North America, Europe, Japan, and
Australia/New Zealand) will then vote on the proposal.  Following that the
IAU FITS Working Group will then conduct a final vote to approve or
disapprove the proposal.  These rules and procedures are more fully
described at http://fits.gsfc.nasa.gov/iaufwg/iaufwg_rules.html.

William Pence
Chairman, IAU FITS Working Group

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Proposal 1:

        Recommendation to Incorporate the "Variable Length Array"
           Facility in Binary Tables into the FITS Standard


The "Variable Length Array" FITS data format that is described in Appendix
B.1 of the FITS Standard is now used by a number of major data analysis
packages.  Examples of current usage include the "Redistribution Matrix
Files" (RMF), widely used in X-ray astronomy to store calibration
information, and the pixel mask files used in the IRAF system.   Many of
the general software libraries for reading and writing FITS files that
are documented on the FITS Support Office web site currently support
this variable length array format in FITS binary tables.

Appendix B.1 is not an official part of the FITS Standard and is included in
that document for informational purposes only.  Because the implementations
described above have now fully demonstrated the usefulness and importance
of the Variable Length Array Facility, it is recommended that Appendix B.1
be officially approved and incorporated into the FITS Standard in its
entirety, with the following proviso:

"Because some software systems may not support FITS tables that use the
variable length array format, the producers of FITS data products should
consider the capabilities of the likely recipients of their files when
deciding whether or not to use this format, and as a general rule should use
it only in cases where it provides significant advantages over the simpler
fixed length array format."


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Proposal 2:

        Recommendation to Incorporate the "Multidimensional Array"
           Convention in Binary Tables into the FITS Standard

Appendix B.2 in the FITS Standard describes a "Multidimensional array"
convention that uses the TDIMn keyword to define the dimensionality of
arrays that are contained in binary table columns.  Many FITS files now use
this convention and contain the TDIMn keyword.  Appendix B.2 is currently
not an official part of the FITS Standard and is included in that document
for informational purposes only.  The widespread usage of the TDIMn keyword
demonstrates the usefulness and importance of this convention, and thus it
is recommended that the "Multidimensional array" convention described in
Appendix B.2 be officially approved and incorporated into the FITS Standard
with the following 2 modifications:

1.  When the IAU FITS Working Group voted to approve the NOST FITS Standard
in October 2000, it did so with the following modification to the text in
Appendix B.2:

     It is noted that the following sentence in B.2, "The size implied
     by the TDIMn keyword will equal the element count specified in the
     TFORMn keyword." is not valid in the case of variable length array
     columns. This sentence should be replaced with wording similar to
     the following: "The total number of elements in the array equals
     the product of the dimensions specified in the TDIMn keyword.
     This size must be equal to the repeat count on the TFORMn keyword,
     or, in the case of columns which have a "P'' TFORMn datatype,
     equal to the array length specified in the variable length array
     descriptor (see Appendix B.1). In the special case where the
     variable length array descriptor has a size of zero, then the
     TDIMn keyword is not applicable.

2.  Delete the last 2 sentences of the 3rd paragraph that mention other
conventions for storing variable-length character strings and
one-dimensional arrays of fixed-length strings.


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