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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: Chris Jang
christopher.jang at yahoo.com
Date: Wed May 21 12:34:38 CDT 2008
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.
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).
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