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[fitsbits] Start of the CONTINUE keyword Public Comment Period
Rob Seaman wrote:
Perhaps the discussion from 1993 and 1994 could be included verbatim, or linked by thread off the web page? I'd hate to hold a debate on a topic that was already batted around a dozen years ago. There is a link on the registry web page to the (very large!) set of comments that were made about this convention when it was first introduced, but the archived FITSBITS discussions for this time period are just broken up into monthly text files. You have to scan through the whole text file to pick out the relevant postings. It would take a lot of editing to make a file just containing the CONTINUE thread. Is the registry page the entire text of the proposed convention? Like Tom said, you need to cover the obvious corner cases, at least by verbiage like "it is undefined what string is conveyed if a card ending is '&' is not followed by CONTINUE". What you see is the entire existing text of the convention, but I plan to augment it with some additional text, based on the comments that are made here during the public comment period. 1) Couldn't the reordering question be dealt with via appending &NNN instead of &? .... 2) What is the reason for not strictly requiring that such a continuation string end with ampersand-quote? .... These are valid questions, but they are a bit 'off-topic' since the purpose of the registry is to document existing conventions, not defend the way they were designed. If we were designing a new continuation convention now we might do things differently. 3) One suspects a number of conventions will depend on valueless keywords. Agreed. The ESO HIERARCH keyword (which will be submitted for inclusion in the Registry in the near future) is another well known example that is somewhat complementary to the CONTINUE convention. The HIERARCH keyword convention effectively allows keyword names much longer than the 8-character limit of real keywords The CONTINUE convention, however, is different in providing a more general capability that could be used, for instance, within any other convention. Deleting a CONTINUE card could in principle change the meaning of any header in arbitrary ways. As you further discussed in a subsequent posting, this CONTINUE convention could be used in principle with any string-valued keyword, including the mandatory or reserved keywords like TFORMn, TTYPEn, EXTNAME. In practice, however, the continue convention has mainly only been used for very instrument-specific keywords like TDDES12 = 'D[0~3] & E[0~63] C[(S[msLimit1]~S[msLimit2]),((S[msLi&' CONTINUE 'mit2]+1)~S[msLimit3]),((S[msLimit4]+1&' CONTINUE ')~S[msLimit5])] ' I wonder if perhaps we shouldn't rather be discussing how best to add this capability to the core FITS standard. This was one of the reasons for setting up the registry in the first place. The first step is to simply document the existing convention in the registry; as a second step, this may lead to a wider discussion of how this sort of capability could be added to the FITS standard. Back in 1993 when this convention was first discussed, we failed to reach any consensus, largely, I think, because many people at that time felt that there was no compelling need for any keyword strings longer than 68-characters. In the rare cases where anyone need longer strings, ad-hoc work-arounds were devised, rather than coming up with a general solution to the problem. Maybe this thinking has changed in the past 14 years(?). If enough people agree that this is an issue worth addressing, it should not be hard to come up with a technical solution for handling long string keyword values (not necessarily identical to the current CONTINUE convention) that could be considered through the official approval process for inclusion in the FITS Standard. Bill Pence -- __________________________________________________ __________________ Dr. William Pence NASA/GSFC Code 662 HEASARC +1-301-286-4599 (voice) Greenbelt MD 20771 +1-301-286-1684 (fax) |
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