Nowadays, most of the commercial solutions for visually
impaired localization and navigation assistance are based on
the Global Positioning System (GPS). However, these
solutions are not suitable enough for the visually impaired
community mainly for two reasons: the low accuracy in urban
environments (errors about the order of several meters) and
signal loss due to multi-path effect or line-of-sight
restrictions. Moreover, GPS does not work if an insufficient
number of satellites are directly visible. Therefore, GPS
cannot be used in indoor environments