[fitsbits] start of Public Comment Period on CONTINUE Long Kwd convention

[Harro Verkouter]

Hi all,

I've been following all discussions about the proposal to add conventions to the FITS standard and this one in particular.

On 26 Jun 2015, at 08:09, Tim Pearson <tjp at astro.caltech.edu> wrote:

> On Jun 19, 2015, at 3:07 AM, Lucio Chiappetti <lucio at lambrate.inaf.it> 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 well known CONTINUE Long String Keyword convention in the FITS Standard.
> 
> A couple of comments:
> 
> 1. "It is recommended that the order of the keywords in FITS files be preserved". Can we not say that the order of "commentary" keywords,  CONTINUE, COMMENT, and HISTORY, is significant and MUST be preserved? (i.e., any reader that interprets these records must do so in the order in which they are presented). A reader that shuffles CONTINUE keywords is broken. The associated text in 4.1.1 says CONTINUE is only a convention, but with this change to the standard it is not.
> 
> 2. I don't see any limit specified on how long a continued string can be. Shouldn't the standard specify some minimum a conforming reader should be able to handle, e.g., 1000 characters, or 2^32 characters?
> 
> 3. "Also, any ‘orphaned’ CONTINUE keyword records should be interpreted as containing commentary text in bytes 9 – 80 (similar to a COMMENT keyword)." I strongly recommend making orphaned CONTINUE keywords illegal; their presence almost certainly indicates an error on the part of the writer which should be flagged by the reader.
> 
> Some opinions:
> 
> 1. I'd really like to see some standard way to tag a FITS file with the version of the standard that it is following, now that we have multiple versions.
> 
> 2. Although I welcome this long string convention, I'd prefer to see the standard find a more general way to allow any header record to span more than 80 characters. "Another technical team has been considering a *new* convention for long keyword name and extended character set. Since this is a new proposal, it will be most likely announced for a Public Review Period later and  separately." Shouldn't we wait for this? Will it be compatible with the CONTINUE convention?

I agree with this. I'd rather leave the proposed convention what it is: a documented convention. There are issues with how to interpret the CONTINUE - does it apply to the value, the comment, both?

Considering that there is a need for longer keywords and/or comments I think it might be more profitable if the FITS standard came up with a better solution.

One suggestion that I keep coming back to is to store the keyword-value pairs in an ASCII table extension with two columns KEY and VALUE of desired maximum length. If the table is left as last HDU in the file, it can be extended easily as needed (or one can pre-allocate a number of rows in the table, any FITS reader will readily accept that).

If the keywords should apply to specific HDU(s) in the file, extra columns like EXTNAME, EXTVER could be added such that a reader can easily filter/aggregate all keywords applicable to a specific extension found in the file, not unlike a database query.

cheers,
harro verkouter


> 3. I'd prefer to see commentary on previous versions of the standard that is irrelevant to someone implementing the standard moved to an appendix on "changes to the standard" (e.g., the new text "Earlier versions of this Standard only defined single string key- words as described in the previous section. The Standard now incorporates a convention (originally developed for use in FITS files from high energy astrophysics missions) for continuing ar- bitrarily long string values over multiple consecutive keyword records."). A standard should be a formal, precise, and concise document.
> 
> Tim
> 
> Timothy J. Pearson
> Research Professor in Radio Astronomy
> Cahill Center for Astronomy and Astrophysics
> Mail Code 249-17, Caltech, 
> Pasadena, California 91125, USA
> E-mail:    tjp at astro.caltech.edu
> Telephone:   +1 626 395-4980    
> 
> 
> 
> 
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