lat/lon to time offset database

Robert Elz kre at munnari.OZ.AU
Thu Feb 3 20:59:26 UTC 2011

    Date:        Thu, 3 Feb 2011 14:27:29 -0500
    From:        Larry Ober <larry.ober at>
    Message-ID:  <5C437F3DECC04DDBA730DC02BA7E00C1 at OfficePC>

  | Basically it just seems dumb that I need to tell my GPS what time zone =
  | it's in. LOL

Unfortunately it is the only way that works reliably - you (or someone)
have to set it (if you have a 3G or something interface, as well as a
GPS receiver, the local phone company may broadcast local time, and
you could work out the timezone offset from that (or of course, you could
just use their time setting...)

The problem is that even if you do all the work that others have suggested,
to collect all the boundary data (and you could actually convince yourself that
your data actually matches the actual practices - which means that the
nominal political boundaries aren't always appropriate), you still end up
with just knowing the zone you're in, and not necessarily the correct

You can believe what's in the database, but that's only accurate if your
device has a current copy, the data changes many times a year.

If your device has the ability to fetch updated database copies when they're
needed, then it must be connected to the net somehow, and if it is, it
can probably make use of that to find some local system with local time
that you can get.

Time seems like it really ought to be simple to deal with, unfortunately
it is absurdly complex.


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