[tz] Dealing with Pre-1970 Data
lester at lsces.co.uk
Fri Aug 30 08:41:38 UTC 2013
David Patte ₯ wrote:
> Though it has been handy to have some pre-1970 data within the tz database, I
> don't see that it is the best solution for historical tz data in the long run.
> It is clear that that going back far enough in time there is a different LMT for
> every 15 seconds of latitude.
Only since 1884 ;) But even then as Paul as said, timezones where not actually
agreed on, only where the base UTC time was defined. The 'local time' was still
synchronised to the sun overhead at noon, hence there was no 'zone'
I think I need to elaborate on why some of this history IS important. Up until
comparatively recently much historic material has been 'timestamped' by local
time + location. This makes 'normalising' times for a genealogical comparison
difficult as one then has to look up information as to the time offset from UTC.
Sound familiar? PHP has now added a nice 'timezone' facility which provides this
lookup, and we can NOW store data as UTC timestamp + location and it will
provide a time display as either local time, UTC or any other location for
comparison with local events world wide.
Since the PHP offsets are generated currently from TZ the next question would be
"how does one fix the currently missing data and flag where data IS
speculation?" Tinkering with 'history' when that has already been used for
storing normalized data is my own concern. I can probably pass the buck to
Derick who currently maintains the Date/Time classes, but he simply 'updates'
from the provided data. Moving forward is it going to be necessary to maintain a
separate 'history' just to keep data from being corrupted? Adding a version
stamp to a timezone so we know what was used?
I presume Stephen is doing the same thing in Java, so I am perhaps a little
surprised if he is now back peddling on getting a common historic base here!
Lester Caine - G8HFL
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