[fitsbits] new WCS papers

[Don Wells]

Dear Friends of FITS WCS,

Eric Greisen writes [on 2001-12-13]:
 > .. versions of Papers I, II, and III..
 > My home page.. [has] direct links..
 >        http://www.aoc.nrao.edu/~egreisen/

The current versions, available at the above URL, are dated 2001-12-31
for WCS-I, 2001-12-12 for WCS-II and 2001-12-31 for WCS-III (the page
numbers in the list of corrections appended below refer to the
pagination of these versions).

		      -=- CDELTis and PCj_is -=-

When I first examined the post-FITS-BoF version of WCS-I, one month
ago, I was dismayed to find that the CDELTis keyword had been
resurrected and that PCj_is had replaced the CDj_is. My first reaction
was a visceral '*NO*, we decided that a long time ago!', but then I
examined the list of reasons given in Sect.2.1.1. The first four
reasons, while valid and important, were insufficient to change my
mind.  But reason number 5 asserts that 'Paper IV will show that some
instruments require distortion corrections before, and others after
the linear transformation matrix'.  Because a draft of paper IV has
not yet been provided, we must take this assertion on faith.  I have
faith in the authors, so this argument is decisive for me: I accept
the change to CDELTis and PCj_is as described and justified in WCS-I.

		   -=- Compliments to the chefs -=-

General: The use of colors to indicate various revisions of the texts
    is quite effective.

WCS-I: The intricate wording of the general rules and defaults, the
    details of keywords for tables, the scholarly units tabulation and
    the masterful discussion of coordinate dimensionality are truly
    impressive.  I got a good laugh from the discussion of GIPSY
    conventions at the end of Section 2.2; anyone who thinks that it
    is possible to write standards with airtight rules should consider
    how the clever GIPSY designer devised conventions which go beyond
    the intended limits, the 'spirit', of the old FITS header rules,
    while not in fact violating the 'letter' of those rules!

WCS-II: All of us have known for many years that this paper is
    destined to be a landmark of the astronomical literature.  I
    assumed that the new draft would have nothing new, and so was
    pleasantly surprised to encounter the excellent tutorial
    discussion in Section 7.5.  Section 7.6, which presents a header
    for an image of the Earth from Cairo to Athens, is magnificent!
    It constitutes a convincing argument that our WCS notation will be
    usable for a wider variety of problems than the astronomical cases
    which have motivated us to work on WCS for so many years. The
    lunar image example in Section 7.9 reinforces this conclusion.

WCS-III: The new discussion and examples of Section 4 greatly
    strengthen this fine paper; I am impressed that the whole set of
    dispersing spectrometers can be described with so terse a
    notation.  The tutorial discussion in Section 5 illuminates a
    subtle but important technical point about wide-field
    spectroscopic imaging which has been largely ignored in the past.

			 -=- Exhortation -=-

These three papers have been available from the URL given above for
more than a month.  Only a few comments have been received by the
authors; it appears to me that none of them raise issues which should
cause us to delay committee action further [*].  I conclude that the
process has converged (at last).

At the ADASS'2001 (Victoria) FITS BoF session, held on the afternoon
of 2001-10-01, the following resolution was approved without dissent:

    "This assembly, finding that the proposed state of the basic WCS
    papers is acceptable, directs that 
    (a) Eric & Mark complete the drafts of papers I, II and III, and
    (b) that these drafts be submitted to the regional FITS committees
        and considered by them expeditiously.

    Mark & Eric are requested to produce, as soon as possible, a
    working draft of paper IV for co-author and then public comment."

In my opinion, Mark, Eric and Frank have satisfied the intent of this
resolution regarding WCS-I, -II and -III.  

I recommend, as IAU-FWG Chair, that Peter Teuben ask whether any of
the North American FITS Committee members have anything else to say;
if not, I recommend that he proceed to call for a vote on a resolution
worded something like this: "The North American FITS Committee
approves the WCS-I, -II and -III papers in their versions of
yyyy-mm-dd, and recommends their approval by the IAU-FWG to become
part of the FITS standard."

I encourage Mark, Eric and Frank to produce a draft of WCS-IV ASAP. 

Obviously, any <fitsbits> or <fitswcs> readers who want to propose any
more modifications to the three papers should propose them *now*.

[*] In a posting to <fitswcs> on 2001-01-01, Steve Allen raised the
    issue of concatenation of transformations; I will address this
    issue in a separate posting on <fitswcs>.

			    -=- Trivia -=-

WCS-I,Sect.1, p.2: In "Because of this wide usage, it forms..", the
    'it' probably should be 'they' in order to agree in number with
    the apparent antecedent.  Actually, it might be better to repeat
    the antecedent.

WCS-I,Sect.2.1, p.3: In footnote 2, 'aberation' should be
    'aberration'.

WCS-I,Sect.2.1.1,p.4:  At the end of the fourth bullet, 'until'
    doesn't feel right to me; perhaps it should be 'to'. 

WCS-I,Sect.2.2,p.6,l.3:  In '..widespread and relatively natural..', I
    recommend that the word 'relatively' be omitted.

WCS-I,Sect.2.2,p.6:  In the last paragraph of Sect.2.2, 'unforseen'
    should be 'unforeseen'.

WCS-I,Sect.2.5,p.7:  In the last sentence of Sect.2.5, the verb 'is'
    should be 'are'.

WCS-I,Sect.4,p.9:  In the last sentence of the first paragraph of
    Sect.4, the text "..units of a ``s'' might.." seems awkward to me;
    perhaps 'a' should be 'an'?

WCS-II,Sect.5.6.3,p.25:  In the second paragraph, 'non-differentable'
    should be 'non-differentiable'.

WCS-II,Sect.6.2,p.26:  In the midst of the third paragraph, "..the the
    older keywords.." should be "..the older keywords..".

WCS-III,Title,p.1:  "Francisco G Valdes" should have a period after 'G'.

WCS-III,Sect.8.1,p.11:  In the next-to-last sentence of the last
    paragraph of Sect.8.1, 'affects' should be 'effects'.

I note that this list of trivial corrections differs completely from
the list posted by Pat Wallace ten days ago; I didn't find his
corrections and he didn't find mine. This suggests that other readers
should be able to find some other corrections.

Regards,
Don Wells [Chair, IAU FITS Working Group]
-- 
  Donald C. Wells      Scientist - GBT Project        dwells at nrao.edu
                    http://www.cv.nrao.edu/~dwells
  National Radio Astronomy Observatory                +1-434-296-0277
  520 Edgemont Road,   Charlottesville, Virginia       22903-2475 USA
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