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

[William Pence]

Hi Ritchie,

Your suggestion of how to continue the comment in long string keywords 
over additional null string CONTINUE keywords is quite clever.  I will 
probably steal this idea and implement it in the next release of 
CFITSIO.  I also support the suggestion to add an example to the 
documentation about this convention that illustrates this usage.

However, I doubt if there would be much support for extending this 
convention to other keyword data types (where the value can easily fit 
on a single header keyword) simply to be able to continue the comment 
field over multiple keywords.  For one thing, the keyword shown in your 
example, namely

INTKEY  = 1245678901234&  / Optional

does not conform to format of any of the currently allowed keyword data 
types.  My impression is that most FITS users find it quite acceptable 
to simply write a long comment over multiple COMMENT keywords, often 
times just preceding the keyword itself.

regards,
Bill


On 6/24/2015 2:29 AM, van Nieuwenhoven, Richard wrote:
> Hello,
>
> first a small introduction because I am new in this mailing list. I am a
> developer of the java nom-tam-fits library (of Tom Mc Glynn). Together
> we moved the nom-tam-fits library to github
>
> (https://github.com/nom-tam-fits/nom-tam-fits)
>
> where we are now working to adapt the library to the current needs of
> the users. Excuse my bad English but I am not a native speaker.
>
> One of the issues we have struggled with in the last months is the
> longstring behaviour together with the possibilities of long comments.
>
> Our users where wondering why so much of the comments is thrown away
> depending of the length of the string. When a string almost fills up the
> space the comment is "gone" (with longstrings enabled it happens every
> time all the cards are "filled" with data.
>
> Now we found a "hack" in the specification to allow keeping longer
> comments by splitting the string over multiple lines even is there would
> be enough space for the string in less cards. then spread over multiple
> lines there is enough space also for longer comments.
>
> In the current specification I did not wanted to go to extreme
> situations by using string continues like this:
>
> STRKEY  = 'This is a very long string keyword&'  / Optional
> CONTINUE  '&' / very very long comments that must be
> CONTINUE  '' / split over a very big amount of lines
>
> because I can imagine that other implementations would not expect such
> "strange" usage. But if the new specification explicitly includes such
> an usage it would be a great help for the developers.
>
> My next proposal is to rename the long-string feature to a long-value
> standard. Why limit long values to strings? Why not use it for all values?
>
> INTKEY  = 1245678901234&  / Optional
> CONTINUE  567890& / very very long comments that must be
> CONTINUE  / split over a very big amount of lines
>
> That would not only allow for values with an unlimited level of
> precision but also for very long comments. The COMMENT keyword is no
> alternative here because it can not be automatically detected if the
> COMMENT has a relation to the previous card.
>
> The same accounts for the COMMENT keyword. Currently the comment keyword
> states a COMMENT with no possibility to write a comment that expands
> over multiple lines and distinguish (automatically) it from multiple
> separate comments.
>
> So in short I propose to officially allow:
> 1. empty string value continues to store longer comments
> 2. use the "long" technique for all value types
> 3. extend the long technique to the COMMENT keyword.
>
> Any thought’s on these feature requests? I am no expert on the standard,
> just an open source developer grown into the standard, so it could be
> that I have overseen other possibilities to achieve the user requests.
>
> 	Ritchie
>
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-- 
____________________________________________________________________
Dr. William Pence    Astrophysicist     William.Pence at nasa.gov
NASA/GSFC Code 662     [Emeritus]       +1-301-286-4599 (voice)
Greenbelt MD 20771                      +1-301-286-1684 (fax)