Subject: Minutes of the OGIP FITS standards panel meeting

From: [email-masked] (William Pence)
Date: Thu, 1 Jul 1993 15:24:29 -0400

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	| MINUTES OF THE OGIP FITS STANDARD PANEL MEETING 1993 June 30 |
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The second meeting of the OGIP FITS Standards Panel (OFSP) was held on 1993 June 30. 

Panel members present: - B.Pence (chair), M.Corcoran (ROSAT), T.McGlynn (GRO),
	A.Rots (XTE), L.Angelini (HEASARC).  Absent: I.George (HEASARC)
        (George gave his proxy vote to Angelini for this meeting).  R.Fink
        resigned from the panel and as yet a replacement from Code 630
        has not been appointed.

Others present - None

Summary of Discussions & Recommendations:
-----------------------------------------

The main business of the meeting was to discuss and make a final vote on the 
4 proposals that were made at the previous meeting:
        
a) Use of underscores vs hyphens in keyword names
b) EXTNAME, EXTCLASS & EXTTYPE keywords 
c) RA & Dec keywords
d) Catalog source ID keywords

More details are given below, but in the end the OFSP approved the
first 3 proposals with minor modifications. It deferred a vote on the
the last proposal and instead proposed a new recommendation which will
be circulated for comments on the HEAFITS mail list server.

Full Minutes
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1) On the use of underscores and hypens in FITS keywords and column names:

The panel agreed that it was useful to  recommend that only one of these
punctuation type characters be used in FITS keyword names and in FITS
table column names (i.e., in the value field of the TTYPEn keywords) in
order to eliminate needless debate over which character to use when
creating new keyword names and to reduce confusion and errors on
the part of software developers and users when entering keyword names.
After some discussion the panel voted (5-1) in favor of using underscores and
to discourage the use of hypens except in two circumstances:  (1) when
there is already a well established precedent for using a hyphen (e.g.,
in the 'DATE-OBS' keyword) or when (2) the hyphen is specifically used
to represent a minus (negation) sign.  The full text of this OFSP
recommendation (R1) will be distributed separately on the FITSBITS and
HEAFITS mail list servers

2) On the proposed new EXTCLASS and EXTTYPE keywords to provide a
hierarchical classification scheme for the various types of FITS
extensions used within the OGIP:

The Panel reviewed the comments that had been received in response to
circulating a draft of this proposal on the FITSBITS and HEAFITS mail
list servers.  Most of the comments dealt with the confusion between
the usage of the existing EXTNAME keyword and the proposed new EXTCLASS
keyword.  The problem with using the EXTNAME keyword for any new
precisely defined purpose is that different groups are already using
the EXTNAME keyword in a variety of mutually incompatible ways, so it
would be impossible to impose a new convention for this keyword without
requiring that some gromps modify their existing software and FITS
files which could be very costly.   The reason for this variety of
usage is that the FITS standard, which defines the EXTNAME keyword,
provides almost no guidance in exactly how it should be used.

Given this situation, the Panel felt that it was preferable to invent a
new keyword (EXTCLASS) which will be used in a well defined way within
the OGIP.  The Panel then approved the EXTCLASS/EXTTYPE proposal by a
6-0 vote with some minor modifications to the text.  The full text of
this recommendation (R2) will be distributed separately on the FITSBITS and
HEAFITS mail list servers.

An action item on the Panel is to develop and maintain a list of
permitted values for the EXTCLASS and EXTTYPE keywords within the
OGIP.

3)  On the proposed new RA and DEC keywords giving the position of the
observed object, the telescope pointing, and the spacecraft axes:

The Panel reviewed the comments on the FITSBIT mail list server
about this proposal.  Some of the comments questioned the need
for these new keywords, suggesting instead that the standard
World Coordinate System (WCS) FITS keywords already provide this
information.  But the Panel agreed that this was not the case, and
that the proposed new RA and DEC keywords supply additional information
and that they can also be used in cases where the WCS keywords 
would be inappropriate (as in some Binary table extensions).

There was some discussion of whether the KEYWORD names should be
shortened to 6 characters to enable a 2 digit sequence number
to be added in cases where the dataset contains multiple objects
or multiple telescope pointings.  Most of the Panel did not favor
this idea, and preferred to keep the more legible keyword names
which are up to 7 characters long.  

The Panel accepted the suggestion (from Pat Wallace) to clarify the
wording of the EQUINOX keyword, and further, to recommend that the
EQUINOX always be either 1950.0 or 2000.0, with 2000.0 being strongly
recommended for all new data sets.

The Panel then approved this proposal by a 6-0 vote.  The full text of
this recommendation (R3) will be distributed separately on the FITSBITS and
HEAFITS mail list servers.

4) On the proposed catalog name and ID keywords:

A number of comments received on this proposal questioned the need for
splitting the catalog name and catalog ID number into 2 separate
keywords.  The Panel agreed that there was no compelling reason to have
2 keyword instead of just one string keyword giving both the standard
catalog appreviation (from the A&A Suppl articles by Fernandez et al.)
and the catalog number.  It was further decided that it would be better
to give the full bibliographic reference to the catalog, if needed, as
a series of COMMENT keywords, rather than inventing a new keyword
(CATREF) for this purpose, since it is unlikely that software would
need to read the value of this keyword.

Due to the extensive changes that were made to this proposal, it was
agreed that Corcoran would circulate the new proposal on the HEAFITS
mail list server for further comments before making a final vote on
it.

The next meeting of the Panel will be held on July 21st.