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[DPRG] digital compass in my car went crazy in Canada
Subject: [DPRG] digital compass in my car went crazy in Canada
From: dpa
dpa at io.isem.smu.edu
Date: Wed May 21 13:00:33 CDT 2008
Hi Chris,
you wrote:
> Hi, I have a small experience with a digital compass.
>
> I was driving out of downtown Vancouver this weekend and the normally reliable
> digital compass in my car went crazy. I was heading south but the compass
> indicated north. Then as the car was on a bridge away from downtown, the
> compass flipped back to south. It was basically acting crazy until leaving
> Canada. It's normal now.
Don't know if this is related, but I borrowed a Brunton recently
from the SMU geology department that had just been used for some
field work in Alaska, and I was surprised to find that the correction
for magnetic variation pointed almost due east! In Dallas the
correction is about 4.5 degrees east, so everything was off
significantly until we reset the compass.
Here's a map of the location of the magnetic north pole from the
Canadian geological survey:
<http://gsc.nrcan.gc.ca/geomag/nmp/northpole_e.php>
and you can see that the north magnetic pole is in fact in
northern Canada.
The $GPRMC record from an NMEA standard GPS includes the local
magnetic variation in fields 10 and 11, and that information is
really required to correct compass headings to match lat/lon
locations. This may be unrelated to what you observed, but it
might not be surprising if the digital compass doesn't correct
for magnetic north.
> So I was thinking the Kalman filter in the compass had gone crazy due to the
> latitude (but are the magnetic lines that much different between Seattle and
> Vancouver?) and EMF from all of the infrastructure downtown.
>
> Anyway, it is a lesson about guidance. In an urban environment, you can't
> necessarily rely on a compass. GPS is spotty too due to tall buildings. So the
> only things you can rely on are dead reckoning and inertial guidance (unless
> you have TERCOM or otherwise some optical scene recognition and registration).
So Chris, we would love to see an outdoor robot do the DPRG
ORC challenges with vision alone, optical flow, terrain mapping,
scene recognition or whatever. Lots of builders think that
ultimately the whole navigation process might be accomplished
visually. But it's not clear how to get from here to there.
How are you progressing?
best,
dpa
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