[time-nuts] OT - GPS and North
Brooke Clarke
brooke at pacific.net
Mon Nov 23 00:22:25 UTC 2009
Hi Antonio:
That's an interesting question.
It turns out that one of the key military applications of GPS, in addition to
position and time, is to find North to high accuracy. This is needed to be
known to better that one grad (1/6400 of a circle). In that past it was done
using a theodolite integrated with a gyroscope (AG8 (Kern DKM1) North Finding
System). This system was heavy, cost the government about $250k and was very
easy to break.
http://www.prc68.com/I/Alidade.shtml#AG8
I think starting with the PLGR96 and now the DAGR there are two or more methods
of accurately finding North.
http://www.prc68.com/I/PLGR.shtml
http://www.prc68.com/I/DAGR.shtml#GLS
http://www.prc68.com/I/DAGR.shtml#AzD
In one method you place the receiver on stake #1, go to stake #2 (while not
obstructing the antenna to allow carrier phase tracking sats) then at stake #2
press enter and the GPS gives you the bearing and distance between the stakes.
In another method two GPS receivers are used. One at stake #1 and the other
first is synchronized to the one at stake #1 then moved to stake #2, press
enter, and go back to stake #1 and reconnect the two units. Again you get
bearing and distance between the stakes based on carrier phase processing
inside the GPS unit.
Have Fun,
Brooke Clarke
http://www.prc68.com
iovane at inwind.it wrote:
> Does a stationary (not in motion) GPS receiver know where the North is?
>
> As far
> as I can understand, it doesn't, isn't it?
>
> Antonio I8IOV
>
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