[iaufwg] CRPIXj clarification vote

[William Pence]

Dear IAU FITS Working Group Members,

It is now time to vote on the proposed change to the new draft FITS
Standard to clarify the definition of the CRPIXj keyword.  This issue
was raised by Bill Thompson when we formally approved the new Standard
document last May.  This should be the final issue that needs to be
resolved to complete the new FITS Standard document.

The text of the proposed change is shown below for reference.  Please
send your vote to me privately by email stating one of the following 3
options:

     - Yes, I approve of the proposed change
     - No, I do not approve of the proposed change
     - Abstain

The voting will remain open for the customary 3 weeks period, but I urge 
you to vote promptly so that we can finish this and turn our attention 
to other business.  I will send out periodic reminders to those who have 
not yet voted.

regards,
Bill

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Proposed change to the wording of the new draft of the FITS Standard:

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

   Rather than store world coordinates separately for each datum,
   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}.
   Integral pixel coordinate values coincide with the corresponding array
   indices, while fractional pixel coordinate values lie between array
   indices and thus imply interpolation.  Pixel coordinate values are
   defined at all points within the image lattice and outside it (except
   along {\em 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]
     Location of the reference point in the image 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 $(1.0, 1.0, \ldots)$.

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____________________________________________________________________
Dr. William Pence                       William.Pence at nasa.gov
NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)