lat/lon to time offset database

Larry Ober larry.ober at
Fri Feb 4 02:05:14 UTC 2011

Thanks Jonathan. It seems to work pretty well.


----- Original Message ----- 
From: "Jonathan Stott" <jonathan at>
To: <tz at>
Sent: Thursday, February 03, 2011 6:16 PM
Subject: Re: lat/lon to time offset database

> 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 
> website. I thought like you that it would be fairly 
> straightforward, but no, it's really not! The result is accessed by 
> webservice through, 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: and 
> 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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