As with all positioning systems where an absolute position measurement is not available, deadreckoning based on integrated angle-rate from gyros and especially doubly-integrated linear acceleration rapidly becomes too inaccurate to use. On vehicle platforms, even poor velocity and heading measurements, from wheel odometers and compass, ultimately will be more useful than their corresponding integrated inertial components.
In the case of a positioning system worn by a pedestrian, where wheel odometry obviously is not available, acceleration and turning signatures of walking are useful. In the simplest form of pedometry, acceleration signature periodicity is associated with forward velocity, either from purely empirical correlation when true speed is known (such as calibration outdoors with GPS) or constrained by the physics of walking.
A more complicated form of deadreckoning from pedometry is possible by associating different walking signatures from 3axis accelerometer and gyro with walking type and parameters: walking forward, backward, sideways, at a crabbing angle, standing still, moving up/down grades or stairs, or even crawling. A system using particle filter that is self-calibratable via GPS has been developed, and the video below shows its deadreckoning performance in a space where only 6axis acc/gyro is being used. The full system, which allows transition from outdoor normal navigation to calibrated deadreckoning indoors via pedometry (speed and heading), is a power seamless navigation approach for pedestrians.