lat/lon to time offset database

[Marshall Eubanks]

On Feb 3, 2011, at 6:16 PM, Jonathan Stott wrote:

> 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.

Is this a system for Internet users ? 

If so, I have to wonder if it would be more efficient to add this to the IP geolocation databases, which map IP addresses to locations.

These are not perfect, but they are pretty good, and they don't require a finite element map of the major rivers and geopolitical border on the planet. 

Regards
Marshall 

> 
> 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
> 
>