mike cook wrote:
----- Original Message ----- From: "Magnus Danielson"
<mag...@rubidium.dyndns.org>
To: "Discussion of precise time and frequency measurement"
<time-nuts@febo.com>
Sent: Saturday, November 21, 2009 4:05 PM
Subject: Re: [time-nuts] OT - GPS and North
Robert Darlington wrote:
It depends on the GPS receiver. The GPS chipset won't know (it knows
where
it is and can remember where it was to know what direction it's
moving), but
some consumer GPS receivers (Garmin, Magellan) have electronic compasses
built in. My Garmin eTrex Legend does NOT have a compass built in, but
taking about 2 steps in any direction will tell me which way I'm
moving. It
can't do this when stationary. My buddy's eTrex can point north without
moving, but that feature drains the battery faster.
The actual GPS receiver and the navigator is two different things. A
GPS navigator may use additional sensors such as accelerometers and
magnetic sensor to aid in addition to the GPS receiver built into them.
Agreed Magnus, but I dont think any gizmos are required. If the the
positions of the satellites are known, as they must be to enable the
antennas position to be calculated, I think just an extra set of
calculations is necessary to indicate the direction to anywhere else on
the planet (or elsewhere) including the geographic poles. Getting the
magnetic pole directions would need something else I suppose.
Yes, but you don't know in what direction from the unidirectional
antenna. The antenna has no sense of direction, but the receiver knows
very well in what direction relative north each sat is. The NMEA stream
even include the coarse directions.
If you has a steerable directional antenna, several antennas or moveable
antenna, then you can convert the internal directions of the antenna
into a north heading or heading towards anything else.
But a normal unidirectional GPS antenna and associated receiver will be
able to know where it is and from it provide very high precision
direction relative north, but unless you move it or make any other form
of aid, it will not be able to show the heading... but when you move
around in with the car, then it can show it relative to the current
heading of the car... as that forms a vector for which you can relate an
angle... to north or to your intended destination.
Cheers,
Magnus
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
