Geolocation techniques enable many services based on the possibility of knowing instantly the position of people and things, and of distributing ad-hoc and location-specific information to users, for commercial, technical or recreational purposes. Some of these services, like GPS car navigation systems, are already common. But the fast development of new techniques for indoor & outdoor geolocation, already available in labs (e.g. based on mobile phones, RF tags or wifi), enable detailed and continuous tracking, even inside buildings. Less