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Restrict "gregorian" label to only dates in the Gregorian calendar #319
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I agree with the desirability of distinguishing the default mixed Julian/Gregorian calendar from the Gregorian. It does not make sense to call dates "Gregorian" when they are earlier than the invention of the Gregorian calendar and don't conform to the Gregorian calendar rules. Redefining |
I agree with Jonathan that we should avoid making changes that make illegal something that is currently legal in CF. I would therefore favor his suggestion to deprecate |
And while we're at it, what about the |
I very much support this proposal. Equating This might be a separate issue, but I raise here for reference: If |
Hello, Here's my summary of where we are with this issue. Please say if you think that I've misrepresented/misunderstood anything.
It seems like there is support for deprecating The David |
@davidhassell To strengthen your argument in the 5th bullet, many countries/communities did not switch to Gregorian, and therefore continued with the Julian calendar as late as 1923, and may have annotated their observations or data that way. |
@davidhassell Thank you for this summary,which I think captures it all. Referencing the proleptic_gregorian calendar instead of the gregorian, as you suggest in your fourth point, provides an elegant and easy way to update calendar definitions (section 4.4.1, and possibly elsewhere). |
To be clear, does this refer only to the |
Good point, @zklaus. I think that all this applies only to In that case, we need to be clear that the default calendar has changed to |
From the above, it's not clear to me whether or not a strict_gregorian calenadar is or is not being proposed. I think it would be a mistake to include it, and I don't think "strict" is optimal as a descriptor. I'll provide reasoning if it is in fact being proposed here. |
I agree with @taylor13. As I hinted at earlier I can see no specific reason for having a specific |
A I agree with @davidhassell's summary, with the addition of @zklaus that we redefine the default as |
It looks like a consensus solution has emerged:
Does that sound right? @Dave-Allured, would you like to put together a pull request for these changes? Thanks all, |
The changes agreed here will now be incorporated into the wider-ranging changes of #298 "Interpretation of negative years in the units attribute" (#298 (comment)). This not only makes it easier to write up the PR for #298, but will also avoid merge conflicts that are likely to occur if these two issues are treated separately. The PR for #298 will also add @Dave-Allured to the CF authors in recognition of his raising the issue and the work he has done on it (unless he would prefer not) (#298 (comment)). Therefore, when #298 is closed, this issue may be closed as well. Thanks everyone. |
Thanks to @JonathanGregory for putting together the pull request that will close this issue (as well as #298). This PR (#331) should be merged on 23rd July, three weeks from today, if no concerns are raised. |
There have been no further comments for three weeks and sufficient support has been expressed, so this change is therefore accepted according to the rules. I have merged #331. Thanks to all contributors to the discussion, especially @Dave-Allured, who raised this issue. |
Summary of Proposal
When using specifically the
gregorian
calendar attribute with time coordinates, restrict the time range to only dates in the real-world Gregorian calendar. That is, date/times no earlier than 1582 October 15 00:00:00.Usage for dates earlier than the Julian/Gregorian crossover of 1582 October 15 is deprecated but not prohibited, because of possible usage in existing data sets.
The initial proposal is to add this restriction to the
gregorian
label, but leave thestandard
and CF default (unspecified) calendars unchanged.Until now,
gregorian
andstandard
were both synonyms for the default mixed Julian/Gregorian calendar as defined by UDUNITS, and in common usage with netCDF since the 1990's. This proposal would splitgregorian
andstandard
into two separate calendar definitions in CF section 4.4.1.This is a recurring request, such as in issues #148 and #298, and at other times.
Reference: Wikipedia article "Gregorian calendar"
Details
Same as in the proposal for #298, this restriction on dates would apply to both the reference date/time string, and to encoded date/time values.
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