This paper describes recent advances with our earlier developed Personal Dead-reckoning (PDR) system for GPS-denied
environments. The PDR system uses a foot-mounted Inertial Measurement Unit (IMU) that also houses a three axismagnetometer.
In earlier work we developed methods for correcting the drift errors in the accelerometers, thereby
allowing very accurate measurements of distance traveled. In addition, we developed a powerful heuristic method for
correcting heading errors caused by gyro drift. The heuristics exploit the rectilinear features found in almost all manmade
structures and therefore limit this technology to indoor use only.
Most recently we integrated a three-axis magnetometer with the IMU, using a Kalman Filter. While it is well known that
the ubiquitous magnetic disturbances found in most modern buildings render magnetometers almost completely useless
indoors, these sensors are nonetheless very effective in pristine outdoor environments as well as in some tunnels and
The present paper describes the integrated magnetometer/IMU system and presents detailed experimental results.
Specifically, the paper reports results of an objective test conducted by Firefighters of California's CAL-FIRE. In this
particular test, two firefighters in full operational gear and one civilian hiked up a two-mile long mountain trail over
rocky, sometimes steeply inclined terrain, each wearing one of our magnetometer-enhanced PDR systems but not using
any GPS. During the hour-long hike the average position error was about 20 meters and the maximum error was less
than 45 meters, which is about 1.4% of distance traveled for all three PDR systems.