In the literature there are also several works related to
vision based navigation. For example, Soundararaj et al.
[7] proposes a purely vision based navigation technique
which relies on fast nearest neighbor classification for 3D
localization and optical flow for velocity estimation. In the
work of Azrad et al. [8], an object tracking system is
used and the vision-control system enables the vehicle to
track and hover above the target as long as the battery is
available. Kendoul and his colleagues [9] present a visual
navigation system based on pose estimation. In the work
of Yu [10], an experimental study in hovering control of an
unmanned helicopter with a 3D vision system instead of GPS
is described.