[tz] McMurdo/South Pole

Guy Harris guy at alum.mit.edu
Sun Sep 22 07:43:30 UTC 2013

On Sep 21, 2013, at 9:47 PM, Stephen Colebourne <scolebourne at joda.org> wrote:

> The problem I have is that I'm no longer sure I can trust tzdb to
> safely be the guardian of the limited pre-1970 data which it has
> always possessed and which Java has long used. I will be talking to
> Oracle people this week to discuss what options we have for Java
> probably requiring manual workarounds of the damaged data. <shakes
> head in despair>

If you care about getting the *right* answer, the only concerns should be about cases where the current pre-1970 data is known to be correct and the changes will eliminate correct data.  Discarding data not known to be correct could just replace one incorrect answer with another.

If you only care about getting *an* answer, it obviously doesn't matter.

> (BTW, the "everywhere was uninhabited" point does not make sense. An
> uninhabited location would effectively be on LMT,

As per my +1 to Russ Allbery's mail, an uninhabited location is on "mu!" time, unless there are living beings at that location that keep time, or there are humans who keep track of time at that location even though there's nobody there.  (If you're trying to, for example, determine where the Sun is in the sky, or something such as that, at that location at a given time, the entire tzdb is irrelevant.)

> Only locations like McMurdo change from unihabited to inhabited at a known date, and LMT should apply before
> that date)

As far as I'm concerned, the tzdb data needn't say anything about time in a given tzdb zone prior to the establishment of standard time for that zone, and the tz code is entitled to return, for that zone, whatever it wants for times before the establishment of standard time in that zone; my inclination would be to project standard time, without DST rules, back into -infinity.

Other code using the tzdb data could choose what to do; if, for example, that code has an API that's passed a time and a longitude and latitude, they could look up the tzdb zone containing that location and, if the time is prior to the establishment of standard time as official civil time in the region covered by that zone, calculate LMT based on the longitude.

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