A novel way-finding method based on geomagnetic field effects and magnetic tensor measurements for visually impaired users

Many man-made objects contains ferrous materials, the presence of which distort earth magnetic field around them. Motivated by this observation, this paper presents a way-finding method utilizing a magnetic tensor sensor (MTS) to help visually impaired people avoid ferrous obstacles and follow magnetic map for indoor navigation. With two orthogonal pairs of digital three-axis magnetic field sensors, the MTS simultaneously measures magnetic flux densities and magnetic tensor; the latter effectively eliminates the influence of geomagnetic field and enables the use of a single tensor-based parameter Q which increases exponentially when approaching an object for obstacle avoidance. A prototype MTS has been developed and its performance has been experimentally evaluated with two practical applications; outdoor obstacle avoidance and indoor navigation using only 1D map incorporating magnetic waypoints and an improved dynamic time warping method to estimate locations from the real-time measurements and pre-stored map. A method to enhance critical waypoints (such as stair) on magnetic map using vision-based line-detections is discussed.