In the field of assisting people to navigate, it is known to use satellite type positioning systems such as the global positioning system (GPS) or the Galileo system. Those systems require the user to have a satellite signal receiver that incorporates a calculation unit arranged to calculate the position of the receiver on the basis of signals from satellites. When associated with mapping software, such systems are particularly effective. Nevertheless, it is not always possible to pick up satellite signals in certain environments, and in particular inside certain buildings, and for example inside a subway system.
Navigation systems dedicated for navigating inside buildings require the buildings to be fitted with those systems in advance so as to enable a device carried by a user to identify its position by triangulation. That obliges the user to restrict movements to sites that are known to be fitted in that way. Furthermore, the investment required usually dissuades the organizations in charge of running such buildings from installing such systems.
The navigation of users within buildings thus generally remains assisted solely by signaling for providing guidance and identifying positions. That technique for providing navigation assistance is not available to visually handicapped people and it requires lighting conditions that are not always available (e.g. during a power cut).
Proposals have therefore been made for a navigation system making use of an inertial device comprising an inertial unit having gyros and accelerometers, and mechanical connection means between the inertial unit and the user. Knowing the user's starting point, such as the entry to the building, it is possible to determine the track followed by the user in the building by integrating the acceleration and speed-of-rotation signals delivered by the inertial unit. The results of such navigation systems have been found to be encouraging in spite of relatively great inaccuracy that makes it difficult to navigate in buildings having a large density of passageways.
A major portion of such inaccuracy stems from the continuous drift of the sensors, in particular when they are inexpensive bottom-of-range sensors. In order to limit the effects of such drift on track calculation, it has been envisaged that the inertial unit can be secured to the user's foot so as to stop integration of the signal whenever the foot is on the ground. This also makes it possible to reset certain operating parameters when the foot is on the ground, such as resetting the identified position of the inertial unit in the terrestrial frame of reference. The accuracy of the system is thus improved significantly.