[time-nuts] OT - GPS and North

Magnus Danielson magnus at rubidium.dyndns.org
Sat Nov 21 18:32:47 UTC 2009


Tom Van Baak wrote:
>> Does a stationary (not in motion) GPS receiver know where the North is?
> 
> No, a stationary object is a point, not a line or a vector.
> The notion of North (or any direction) has no meaning
> to a point, by definition.

You are mixing things a litte too much here. There is no direction 
within a 0-dimensional space, but a point as it is positioned in a 
3-dimensional space has no problem to have an associated vector pointing 
either to a location or along some field such as the magnetic field.

An electron is a point-charge, and reacts to a magnetic field or the 
electrostatic field.

The antenna is certainly not a point, it is a sizeable object and it's 
phase centrum isn't a point either, it's just a handy approximation.

It's just that normal GPS antennas and receivers isn't built for this 
purpose. A much smaller object than either the antenna or the receiver 
is the SO-8 packaged magnetic sensor you can buy cheaply and sense the 
magnetic field. A GPS receiver can be used to compensate for magnetic 
deviation if needed.

Cheers,
Magnus



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