Subject: Successful demonstration of DATExxxx interoperability

From: Don Wells <dwells at nrao.edu>
Date: Thu, 7 Aug 1997 12:08:15 -0400 (EDT)

Dear friends of FITS (especially the IAU FITS Working Group),

I am pleased to report that the necessary interoperability
demonstration of the proposed DATExxxx agreement has been achieved.

Preben Grosbol used a version of MIDAS to read the FITS test file
which Eric Greisen had produced with a version of AIPS. Preben then
ordered MIDAS to write the data out as another FITS file, which Eric
has read successfully with AIPS. The dates are consistent in the two
systems and two files (see below).  The original test file produced by
AIPS is

    ftp://fits.cv.nrao.edu/fits/data/samples/year-2000/newdate.fits.gz

and the version of this file produced by MIDAS is 

    ftp://fits.cv.nrao.edu/fits/data/samples/year-2000/y2000m1.fits.gz

Header listings are in files "newdate.lst" and "y2000m1.list" in the
same directory.  The command "grep 'DATE' newdate.lst" produces

DATE-OBS= '1979-09-19'         /OBSERVATION START DATE DD/MM/YY
DATE-MAP= '1992-09-18'         /DATE OF LAST PROCESSING DD/MM/YY
HISTORY PUTHEAD DATE-OBS ='        '         / old
HISTORY PUTHEAD DATE-OBS ='19790919'         / new
DATE    = '1997-07-25'                  / File written on yyyy-mm-dd

and command "grep 'DATE' y2000m1.lst" produces

DATE    = '1997-07-29T14:37:32' / Date of writting: DD/MM/YY
DATE-OBS= '1979-09-19'         / MIDAS desc.: O_TIME(1)
HISTORY PUTHEAD DATE-OBS ='        '         / old
HISTORY PUTHEAD DATE-OBS ='19790919'         / new
DATE-MAP= '1992-09-18'         / DATE OF LAST PROCESSING DD/MM/YY

Note that MIDAS appended a time string to the DATE value. I recommend
that all FITS writing code use the new time string capability with
DATE in this manner, even if they don't use it with DATE-OBS etc.,
because it produces a useful unique time-tag in each FITS file.

Preben supplied a second FITS test file, a nice galaxy image, at

    ftp://fits.cv.nrao.edu/fits/data/samples/year-2000/y2000m2.fits.gz

The command "grep 'DATE' y2000m2.lst" produces 

DATE    = '1997-07-29T15:02:58' / Date of writting: DD/MM/YY
DATE-OBS= '1993-05-17'         / MIDAS desc.: O_TIME(1)

I encourage all of you to test the FITS readers of your datasystems
with these files, and to report the results to the FITS community.  
I will be pleased to add DATExxxx test files produced by the FITS
writers of other datasystems to this directory.

Regards,
Don Wells (Chair, IAU FITS Working Group)
-- 
  Donald C. Wells         Associate Scientist         dwells at nrao.edu
                    http://fits.cv.nrao.edu/~dwells
  National Radio Astronomy Observatory                +1-804-296-0277
  520 Edgemont Road,   Charlottesville, Virginia       22903-2475 USA