[time-nuts] OT - GPS and North

[mike cook]

----- Original Message ----- 
From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Saturday, November 21, 2009 4:05 PM
Subject: Re: [time-nuts] OT - GPS and North


>
> Robert Darlington wrote:
>> It depends on the GPS receiver.  The GPS chipset won't know (it knows 
>> where
>> it is and can remember where it was to know what direction it's moving), 
>> but
>> some consumer GPS receivers (Garmin, Magellan) have electronic compasses
>> built in.  My Garmin eTrex Legend does NOT have a compass built in, but
>> taking about 2 steps in any direction will tell me which way I'm moving. 
>> It
>> can't do this when stationary.  My buddy's eTrex can point north without
>> moving, but that feature drains the battery faster.
>
> The actual GPS receiver and the navigator is two different things. A GPS 
> navigator may use additional sensors such as accelerometers and magnetic 
> sensor to aid in addition to the GPS receiver built into them.
>

 Agreed Magnus, but I dont think any gizmos are required. If the the 
positions of the satellites are known, as they must be to enable the 
antennas position to be calculated, I think just an extra set of 
calculations is necessary to indicate the direction to anywhere else on the 
planet (or elsewhere) including the geographic poles. Getting the magnetic 
pole directions would need something else I suppose.

> So a navigator may know, even if on a fixed location, but the GPS receiver 
> does not have that information.
>
> It is important to keep these separated so that they can be discussed 
> properly. I don't want to say stuff like "The actual GPS receiver in the 
> GPS receiver...".
>
> Cheers,
> Magnus
>
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