Subject: PFSP Proposal for 2 new keywords: Note of a FITSBITS post

From: [email-masked] (Ian M George, Code 668, NASA/GSFC, USA (Usque ad mortem bibendum))
Date: Thu, 17 Jun 1993 18:04:04 -0400

Yet another recommendation of the OFSP meeting on 1993 Jun 16 was that 
the OGIP change its use of the EXTNAME keyword, and that two new keywords 
be introduced.

Again, since these new keywords may be of interest to the general FITS
community, the OFSP felt the best forum for discussion of such a proposal
is the FITSBITS exploder, and thus the proposal was posted there (today).
Since some HEAFITS recipients may still not be members of the FITSBITS, 
a copy of the proposal is appended below. However it is **STRESSED** that 
all discussion should take place on FITSBITS.

----------------------- Start of included message ---------------------------
----------------------- (as exploded on FITSBITS) ---------------------------

	-------------------------------------------------------
	|   THE USE OF THE EXTNAME KEYWORD AND THE PROPOSED   |
	|	   INTRODUCTION OF TWO NEW KEYWORDS	      |
	-------------------------------------------------------
					  Version: 1993 June 17

At a meeting on 1993 Jun 16 of the OGIP FITS Standards Panel (OFSP) within
the Office of Guest Investigators (OGIP) at NASA/GSFC, there was a review
of the use of the EXTNAME keyword within the OGIP. 

The OFSP found that it was common practice within the OGIP to use the value
of the EXTNAME keyword to simultaneously describe both the generic *kind*
of dataset being stored, and additional *details* of the dataset. Thus
values of the EXTNAME keyword were being formed by the concatination of 2
or more sub-strings. This gives rise to long, and often user-unfriendly,
EXTNAMEs essentially containing a variety of different pieces of
information. More importantly these strings are apparently incompatible
with a number of IRAF tasks. An example is:
   EXTNAME  = 'GTI_STANDARD'
meaning the dataset is a list of all 'standard' "Good Time Intervals". An 
(admittedly extreme) example is: 
   EXTNAME  = 'SGL_SPEC_STAT_+UNC' 
meaning the dataset contains the positive statistical uncertainties 
on a single spectrum.

Whilst such use of EXTNAME keyword is legal FITS, the OFSP proposes &
recommends the adoption/use of the two keywords listed below. Since this
is an issue likely to be of interest to the general FITS community, the
OFSP would welcome any comments (via FITSBITS) on this proposal. 

Furthermore due to the pressures imposed by currently flying missions
(ASCA, CGRO & ROSAT) there is an extremely urgent need for a convention for
these keywords within the OGIP (& High-Energy community in general). The
OFSP therefore plans to meet again in a couple of weeks to make its final
recommendations. Thus BITFITS subscribers are urged to response with any
comments etc on this timescale. 

THE PROPOSAL 
************

The OFSP recommends the use of the EXTNAME keyword be changed (at least 
within the OGIP), and that two new keywords, EXTCLASS & EXTTYPE be 
introduced:

EXTNAME   - Can be any string & is essentially not used by OGIP s/w
            (NOTE: IRAF can only cope with 6 character strings)
EXTCLASS  - Is a new string describing the sort of dataset stored (see below)
EXTTYPE   - Is a new string available to give more specific details on
            exactly what type of data is stored (see below)

A few examples should make the distinctions between the keywords more
obvious:

1) For various "Good Time Intervals"
   EXTNAME  = 'ABCBEF'          (or whatever you like)
   EXTCLASS = 'GTI'             (some sort of GTI is stored)
   EXTTYPE  = 'STANDARD'        (the GTIs from standard processing are stored)
or EXTTYPE  = 'ALL'             (all times when the instrument is on are stored
                                [no filtering has been applied])
or EXTTYPE  = 'UNKNOWN'         (uncertain what is stored)

2) For various "Events" lists
   EXTNAME  = 'GHIJKL'          (or whatever you like)
   EXTCLASS = 'EVENTS'          (some sort of EVENTS list is stored)
   EXTTYPE  = 'GOOD'            (accepted events [only] are stored)
or EXTTYPE  = 'BAD'             (rejected events [only] are stored)
or EXTTYPE  = 'ALL'             (all events [no filtering] are stored)
or EXTTYPE  = 'UNKNOWN'         (uncertain what events are stored)

The two new keywords follow a logical hierachy, solve all the current
problems, and seem general enough to give us (the OGIP, and general FITS 
community) flexibility in the future. 

----------------------------------- END ---------------------------------- 

Ian M George 					
NASA/GSFC OFSP
1993 Jun 17