[iaufwg] Voting result on the FITS Standard

[William Pence]

Dear IAU FITS Working Group members,

I am pleased to announce that all 22 members have voted and have 
unanimously approved the draft FITS Standard, version 3.0c, as the new 
official FITS Standard document.  However, a number of these votes of 
approval were conditional upon adding a clarification to the document on 
the use of the CRPIXj keyword.  This issue was first raised by William 
Thompson in his email on 06 May 2008.

I privately asked Mark Calabretta and Eric Greisen to suggest a specific 
change to the wording of the document to address this issue.  Below is 
Mark's proposal:

1) Insert the following paragraph at the start of Sect. 8.1:

   Rather than store world coordinates separately for each datum (e.g. as
   is done for random groups data), the regular lattice structure of a
   FITS image offers the possibility of defining rules for computing
   world coordinates at each point.  As stated in Sect. 3.3.2 and
   depicted in Fig. 3.1, image array data are addressed via {\em integral
   array indices} that range in value from 1 to NAXISj on axis j.
   Recognizing that image data values may have an extent, for example an
   angular separation, spectral channel width or time span, and thus that
   it may make sense to interpolate between them, these integral array
   indices may be generalized to floating-point {\em pixel coordinates}.
   While integral pixel coordinate values coincide with the corresponding
   array indices, pixel coordinates are defined at all points within the
   image lattice and outside it (except along conventional axes, see
   Sect. 8.5).  They form the basis of the world coordinate formalism in
   FITS depicted schematically in Fig. 8.1.

2) Remove the italics from "pixel coordinates" on p75 (they are used in
    the first mention above).

3) Change the definition of CRPIXj on p77 to:

    CRPIXj - [floating-point, indexed, default: 0.0]
        Pixel coordinate element of the reference point for axis j,
        corresponding to $r_j$ in Eq. (8.1).  Note that the reference
        point may lie outside the image and that the first pixel in the
        image has pixel coordinates $(1.0, 1.0, \ldots)$.


Does anyone have any comments, suggestions, or objections regarding this 
proposed change?

regards,
Bill Pence

P.S.  I will assume that there are no objections to also fixing 2 other 
typographical issues in the final version of the standard document:

  - Remove the extraneous word "the" in the first sentence of
    section 7.3.4.

  - Update the reference to the HEALPix paper on p120 to MNRAS, 381, 865.

-- 
____________________________________________________________________
Dr. William Pence                       William.Pence at nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
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