[week 4 summaries]
Pedestrian Tracking with Shoe-Mounted Inertial Sensors
There are a bunch of scenarios when a navigation for tracking the location of a person is useful, some are for life saving (locate to rescue firefighters); some are for assistant (personal navigation); and some are for entertaining (AR applications).
The author put forward a pedestrian tracking system NavShoe that leverages inertial sensors for position tracking. It is a compact wireless sensor tuck into the shoelaces and works both for indoor and outdoor applications. The inertial sensor, unlike other tracking approaches which need installed markers or prior instrumentation, can works within a reasonable accuracy in arbitrary unprepared environment. Furthermore, the new system provides an extremely accurate orientation tracker on foot.
A big problem which affects the accuracy of inertial sensor is the accumulated drift error. The NavShoe tries to cope with integrating error by introducing zero-velocity updates (ZUPTs) into the Extended Kalman Filter (EKF). As people walks, his gesture can be classified into two phases: stationary stance phase and moving stride phase. The NavShoe detects the stance phase and applies ZUPT as measurement to break the error accumulation from cubic-in-time to linear in the number of steps.
Another problem comes from the deviation of compass. The distortion of the earth’s magnetic field caused by the metal in the shoes is overcome by a delicate calibration before entering navigation mode. This calibration only needs to be done when we remove the sensor to another shoe.
A bunch of test results are given covering indoor/outdoor experiments and those integrated with GPS’s. The indoor experiment takes 3 shots with predefined route; free-trail (but mostly following the first route) and route involving altitude changes. The results shows good performance with 0.3 percent of the distance traveled in plane and 0.6 in altitude. The experiment of outdoors also obtains similar good performance. By integrated with GPS, NavShoe can deal with ever longer distance but still maintain the accuracy by online calibration of magnetic declination.
In the future, we can also using the foot sensor to increase the head tracking sensor’s accuracy.
Overall, I think this system can be a complement for GPS’s inaccuracy in small scale and dependency on pre-mapped environment. Scenarios that need fine position data or have limited access to the satellite system give this application places in the market.
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