lat/lon to time offset database

Jonathan Stott jonathan at jstott.me.uk
Thu Feb 3 23:16:58 UTC 2011


On 03/02/2011 18:33, Larry Ober wrote:
> I'm a nubie at understanding the ins and outs of timezones so please forgive
> me for my potentially dumb questions.
>
> I am looking at building a small embedded system (No OS) that will require
> determining the local time from the lat/lon of a location. So basically I need
> lat/lon to time offset from "GMT".

I had a go at doing this a few years ago when I was creating the 
earthtools.org website. I thought like you that it would be fairly 
straightforward, but no, it's really not! The result is accessed by 
webservice through earthtools.org, but the data is a few years old now 
and it's not really that accurate.

I basically generated a map of the zones as accurately as I could 
(limited by not having accurate administrative area boundaries) and did 
some processing to reduce the complexity of lookups. I blogged about it 
5 years ago: http://blog.jstott.me.uk/2005/12/01/mapping-time-zones/ and 
http://blog.jstott.me.uk/2005/12/08/time-zone-map-completed/

If anyone has any ideas for how to improve the accuracy or, more 
importantly, map daylight savings time rules (which are even more 
complicated), I'd love to know!

Jonathan




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