[time-nuts] OT - GPS and North

Gary Chatters gcarlistaa at garychatters.com
Sat Nov 21 23:09:30 UTC 2009


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




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