[time-nuts] OT - GPS and North

[bg at lysator.liu.se]

> J. Forster wrote:
>> OK. Sme GPS receivers have magnetic sensors.  What do they do with/about
>> magnetic deviation.
>>
>
> There is a field in one of the NMEA messages for magnetic deviation
> which some GPS receivers fill in.
>
> I do not know where they get the values.  There is a mathematical model
> available from an appropriate agency (I forget which one right now) that
> can be used to compute magnetic deviation anywhere on earth.  The model
> is supposed to be good for about five years before the coefficients need
> to be updated.
>
>
> Gary
>

One model is called the World Magnetic Model

    http://en.wikipedia.org/wiki/World_Magnetic_Model

These models are the magnetic equivialent of the gravity models used to
determine the geoid.

--


     Björn