[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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