[fitsbits] start of Public Comment Period on the Green Bank convention

[Erik Bray]

On 6/19/2015 7:34 AM, Lucio Chiappetti wrote:
> On Fri, 19 Jun 2015, Lucio Chiappetti wrote:
>
> ANNOUNCEMENT:  START OF FORMAL PUBLIC COMMENT PERIOD
>
> This is to announce the official start of a 3-week formal Public Comment
> Period on the incorporation of the so called Green Bank convention in
> the FITS Standard.
>
> This is part of a process to incorporate the most useful, widely used
> registered, and simple conventions (which are valid FITS constructs) into
> the official definition of the standard.
>
> This convention allows to expand a kewyord in a table column (or collapse
> a column with identical values in a keyword).
>
> The proposed text consists just
>
> - in the ADDITION of a new section 8.2.1 in the WCS section (hilighted in
>    green colour)  describing the usage convention
>
> - in the addition of CROSS REFERENCES to it in 7.2.2 and 7.3.2 after TTYPn
>    (resp.  for ASCII and binary tables), aloso hilighted in colour
>
>     and has been prepared by a technical team including L.Chiappetti,
>     W.Pence, A.Dobrzycki, R.A.Shaw and W.Thompson (main editor
>     W.Pence).
>
> - If the proposal is approved a section H.3 will be added to Appendix H
>    describing the update
>
> The proposed draft text is available at
> http://sax.iasf-milano.inaf.it/~lucio/FITS/Conventions/greenbank-upd2.pdf
>
> Supporting material is provided in the FITS Convention Registry at the
> http://fits.gsfc.nasa.gov/registry/greenbank.html

Hi all,

I'm not sure I understand the purpose of including this convention in the FITS 
standard.  Part of this is, I'm sure, out of ignorance.  I have not encountered 
use of this convention in the wild, and I'm not sure what programs use this 
convention or to what purpose, though I'm sure it's popular somewhere or else it 
would probably not be a documented convention.  That said, the proposed addition 
to the FITS Standard says nothing about when or why one would store multiple 
images in a vector column of a binary table.

Perhaps even beyond the question of "why", what this convention does not 
document is how, given an arbitrary FITS file, one would be able to determine, a 
priori, that a binary table in that file represents a collection of images.  If 
a binary table has columns named the same as WCS keywords should it just be 
assumed that that table represents an array of images?  And in what columns are 
the actual image arrays stored, much less auxiliary arrays like errors?

If a software reader *could* somehow determine that a binary table stores a 
collection of images, should it interpret it still as a binary table, or should 
it interpret it, somehow, as a collection of pseudo IMAGE extension HDUs?

On 6/22/2015 9:39 AM, Rob Seaman wrote:
> Hello all,
>
> Two points:
>
> 1) Among other motivations this initiative is in response to discussions
> regarding the future of FITS at the last few ADASS meetings. A forceful
> opinion was expressed by one group that conventions are insufficient
> compared to appearing in the standard.

I'm not sure that anyone expressing that opinion believes that all registered 
FITS conventions belong in part of the standard though. Especially not if they 
don't specify how users of FITS readers should interact with some data model.

Best,
Erik

Best,
Erik