  In this paper, we present an autonomous unmanned aerial vehicle (UAV) landing
system based on visual navigation. We design the landmark as a topological
pattern in order to enable the UAV to distinguish the landmark from the
environment easily. In addition, a dynamic thresholding method is developed for
image binarization to improve detection efficiency. The relative distance in
the horizontal plane is calculated according to effective image information,
and the relative height is obtained using a linear interpolation method. The
landing experiments are performed on a static and a moving platform,
respectively. The experimental results illustrate that our proposed landing
system performs robustly and accurately.
