Draft of FITS standard revision 1.2 available for comment

Richard White rwhite at nssdc.gsfc.nasa.gov
Wed Apr 15 10:24:31 EDT 1998


PLEASE REDISTRIBUTE WIDELY



Call for comments on Revised FITS Standard


The NASA/Science Office of Standards and Tecnology (NOST) Draft Standard
100-1.2, Definition of the Flexible Image Transport System (FITS), is now
available for review and comment. This is a major revision to the previous version 1.1 of the FITS standard that was adopted in 1995.  This Standard is being
developed by a NOST-sponsored Technical Panel.

FITS Technical Panel
Robert J. Hanisch, Chair			STScI
Barry M Schlesinger, Secretary			NASA/FITS Support Office
Allen Farris					STScI
Eric W. Greisen					NRAO
William D. Pence				NASA/GSFC
Peter J. Teuben					UMd
Randall W. Thompson				STScI/CSC(formerly at GSFC/IUE)
Archibald Warnock				A/WWW Enterprises

The purpose of distributing this Draft Revision to the NOST FITS Standard is to
provide for community review and comment.  The Technical Panel will review and
respond to all comments.  The Panel will either incorporate the substance of a
comment into the Standard, or it will instead provide the reasons for not doing
so and describe any revision to the Standard motivated by the comment.  After
the panel has completed review of and responded to all comments, the final
version will be submitted to NOST for certification.  Upon certification, the
final version number will be 2.0.  It will then be submitted to IAU Commission 5
for formal acceptance as the IAU standard.

Copies of the standard are available in two ways: paper copies and access to
electronic copies via the WWW.  Electronic copies are available formatted for
LaTeX, PostScript, gziped Postscript and html.  The electronic versions are
posted on the FITS Support Office web site homepage at
http://fits.gsfc.nasa.gov/

Paper versions may be requested from the National Space Science Data Center
Coordinated Request and User Support Office (CRUSO) at

Coordinated Request User Support Office (CRUSO)
Code 633,
National Space Science Data Center
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771, USA

E-mail: request at nssdca.gsfc.nasa.gov
Telephone: (301) 286-6695
FAX: (301) 286-1635

All comments should be mailed to the fitsbits exploder at
fitsbits at fits.cv.nrao.edu, or posted to the newsgroup sci.astro.fits. 
Dr. William Pence, a member of the technical panel,
will oversee the reading, discussion, and panel response to all comments.
There will be an approximately 3 month period for comments.  All comments
should be submitted by July 15, 1998.

The development of the standard and its certification is supported by the FITS
Support Office in the Astrophysics Data Facility at NASA's Goddard Space
Flight Center.

FITS Support Office
Code 631
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
USA

e-mail:	fits at fits.gsfc.nasa.gov
http://fits.gsfc.nasa.gov/
+1-301-286-6695 


List of Significant Changes Between Versions 1.1 and 1.2 (Draft) of the NOST
FITS Standard

Section            Description of Changes
-------    ---------------------------------------------

 3:       Definitions have been added, deleted, or revised:
           Added: ASCII NULL, DAT, Fraction, Heap, IAUFWG,
                      Mantissa, Primary HDU, Repeat count
           Deleted:   AIPS, CfA, ESO, NOAO, NRAO, STScI
           Revised:   Entry, Floating point, Indexed keyword

 4.6:     New section describing Physical Blocking.  Incorporates some text
          previously contained in Appendix B.

 5.1.2.2: Explicitly states that null-valued keywords are allowed.

 5.1.2.3: Keyword comment, if present, must be preceeded by a slash.

 5.2:     References to ANSI FORTRAN-77 have been removed and
          replaced with explicit definitions of free format values.

 5.2:     Keyword values are restricted to be a single value
          and not an array of values.

 5.2.1:   Fixed format character string values no longer need to be
          padded with blanks to be at least 8 characters long.
          (e.g., XTENSION= 'TABLE' is now a legal keyword record).

 5.2.1:   Previous requirement that reading the data values should
          not require decoding any more than the first eight
          characters of a character string value of a keyword has
          been dropped.

 5.2.2:   Explicitly states that a logical value must consist
          of a single `T' or `F' character, followed only by a
          space or a slash character.

 5.2.3:   Explicitly states that an integer value must not contain
          embedded spaces and is always interpreted as a signed
          decimal value.

 5.2.4:   Explicitly states that a real floating point value must not
          contain embedded spaces. The decimal point is not required,
          so values like 12, and 1E30 are valid, but E30 is not.

 5.2.5:   Fixed format for complex integers is no longer defined.
          Free format complex integer values must be enclosed in
          parentheses separated by a comma, e.g. (14, -45).

 5.2.6:   Fixed format for complex reals is no longer defined.
          Free format complex real values must be enclosed in
          parentheses separated by a comma, e.g. (14.5, -4.5E+5).

 5.4.1.1  Explicitly states that no other keywords may intervene between
          the SIMPLE and last NAXISn keyword in the primary header.
          The SIMPLE keyword must not appear in extension headers.

 5.4.1.2  Explicitly states that no other keywords may intervene between
          the XTENSION and last NAXISn keyword in an extension.

 5.4.2    The description of the DATE and DATE-OBS keywords has been
          modified in accordance with the new Y2000 FITS agreement.

 6.3      Definition of IEEE floating point has been moved to appendix H.

 8.1      Explicitly states that no other keywords may intervene between
          the XTENSION and TFIELDS keywords in an ASCII table extension.

          The TFORM format codes must be in upper case.  Numeric values
          in ASCII tables are always decimal, and never binary, octal,
          hexadecimal, or other representation.

 8.1.5    New discussion about selecting a format appropriate to the
          data.   References to ANSI FORTRAN-77 have been removed and
          replaced with explicit definitions of how each format should
          be interpreted.

 8.2      Definition of the image extension has been added.

 8.3      Definition of binary table extension has been moved from
          Appendix A into the standard itself.   The TFORM format codes
          must be in upper case.

 8.3.4    Explicit definitions are given for the possible display formats.

Appendix A: (new) gives a formal syntax for keyword card images.

Appendix D: (new) discusses time scale issues related to the new
            DATE-OBS keyword format.

Appendix H: (new) defines IEEE floating point formats


-----------------------------------------------------------------------------


Types of keywords that are explicitly allowed in the new FITS standard
-----------------------------------------------------------------------

KEYWORD =                      / the value of this keyword is undefined
XTENSION= 'TABLE'              / string can be less than 8 chars long
REALVAL =                   14 / decimal point is not required for reals
COMPLEXI=            (12, -45) / complex integer value
COMPLEXR=       (12.5, 5.6E-3) / complex real value
DATE    = '2000-01-01T11:45:59.999' / new date format


Types of keywords that are explicitly disallowed in the new FITS standard
-----------------------------------------------------------------------

KEYWORD =               3.1415   Value of Pi (no slash before comment)
KEYWORD =          1,2,3,4,5,8 / arrays of values are not allowed
LOGICAL =                 TRUE / logical values must be only T or F
INTVAL  =                 0777 / must not be interpreted as octal number
INTVAL  =               124 56 / embedded spaces not allowed in integers
REALVAL =            1.34 E+11 / embedded spaces not allowed in reals
REALVAL =                  E20 / number preceeding the exponent is required






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