[fitsbits] Start of the FITS-IDI Convention Comment Period

[Harro Verkouter]

Hi all,

After reading through the document I'd like to make a few comments.  
Some of those apply to the implementation of the/a reader, nonetheless  
they seem to indicate incompatibility between documentation and  
practical use-cases. This is written from the perspective of the EVN  
FITS-IDI data-export software, which has been implemented exactly  
following the Flatters(1999) document [and thereby finding  
discrepancies between documentation and implementation].

* I have noticed that in most cases the order in which the keywords  
are written (also the non-mandatory FITS keywords) may have to be  
identical as in the documentation or else your FITS-IDI file may be  
rejected. I do not know if this situation has changed over the last  
few years, I did not experiment with writing keywords "out-of-order"  
since finding out that it most likely 'breaks' your FITS-IDI file.

* The "SORT" optional keyword to the UV_TABLE header (p.15) does not  
seem to get honoured. Our FITS-writer writes the hard-coded value  
"TB" (Time-Baseline) since that is the order in which the data is  
forcibly written, nonetheless it is never recognized by the reader,  
making the user have to run uvsort (or wossname of the task) to make  
the data recognized as being sorted in TB order. It may well be that  
this behaviour is triggered by our FITS-writer doing something else  
wrong however it is not documented - making it quite unfixable yet.

* I'm glad to see the POLARX/Y situation being somewhat resolved. I  
beg to differ, however, from the statement in the document "The units  
were changed from the meters specified by the earlier documents, but  
seldom used in actual implementations.". Especially since it is  
exactly this early misdocumentation (documentation says "meters", s/w  
interprets them as "arcseconds") that has caused many of our users  
headaches (EVN data).

Cheers,

harro verkouter



On Jun 1, 2009, at 20:53 , William Pence wrote:

> This is to announce the start of the 30-day Public Comment Period on
> the FITS Interferometry Data Interchange (FITS-IDI) Convention for the
> interchange of data recorded by interferometric telescopes,  
> particularly
> at radio frequencies and very long baselines.  This is the 16th in a
> growing series of conventions submitted to the Registry which is
> maintained by the IAU FITS Working Group.
>
> Detailed information about this convention and a sample FITS file that
> uses it are available for public review and comment from the FITS
> registry web page at
>
>               http://fits.gsfc.nasa.gov/fits_registry.html
>
> Comments about this convention may be posted here on the FITSBITS mail
> exploder or the mirrored sci.astro.fits newsgroup.  Minor  
> typographical
> issues may be sent directly to the authors of the convention.
>
> Bill Pence
> (on behalf of the IAU FITS Working Group)
> -- 
> ____________________________________________________________________
> Dr. William Pence                       pence at milkyway.gsfc.nasa.gov
> NASA/GSFC Code 662       HEASARC        +1-301-286-4599 (voice)
> Greenbelt MD 20771                      +1-301-286-1684 (fax)
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