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From: Kai Harrekilde-Petersen on 25 Jan 2010 14:16
Terje Mathisen <"terje.mathisen at tmsw.no"> writes:

> Kai Harrekilde-Petersen wrote:
>> But how on earth can the laptimers actually determine your position
>> (and thus, when you have completed another lap) with such an accuracy,
>> when the "real" reference is only updated every 30 seconds? Sure,
>> more than 4 satelites means more updates, but there is a factor of
>> 3000 between the two numbers to start out with, so even 12 satelites
>> won't make much difference here.
>
> Simple:
>
> GPS decoding is a (very) stateful protocol!

[snip explanation]

Thanks to both Bernd and Terje for the explanations. I guess that
this was one of the times when a wikipedia article is so loaded that
the piece of info I was looking for was the proverbial needle in the
haystack!

I went back and found the relevant section on wikipedia, and as long
as we don't care about the absolute location, but only relative
location, an accuracy of around 2.3m can be achieved. At 350kph, the
car or bike moves with just under 1m/0.01sec, so interpolation should
be safe here :-)


Kai
--
Kai Harrekilde-Petersen <khp(at)harrekilde(dot)dk>
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