Nowadays the unmanned aerial vehicles (UAVs) are getting more and more interest, their velocity and precision make them a powerful tool for a wide range of applications, from aerial photography to search and rescue operations. These systems rely on the global navigation satellite system (GNSS) as primary source of position information for navigation, without reliable signal, a UAV's ability to maintain accurate positioning and autonomy is compromised, for this reason the UAVs are not suitable to work in environments where GNSS signals are either weak or unavailable, so called GNSS-denied environments. However, there are many operations, such as indoor and urban inspections, that take place in GNSS-denied environments that would benefit from the use of a drone.