  The visibility of targets determines performance and even success rate of
various applications, such as active slam, exploration, and target tracking.
Therefore, it is crucial to take the visibility of targets into explicit
account in trajectory planning. In this paper, we propose a general metric for
target visibility, considering observation distance and angle as well as
occlusion effect. We formulate this metric into a differentiable visibility
cost function, with which spatial trajectory and yaw can be jointly optimized.
Furthermore, this visibility-aware trajectory optimization handles dynamic
feasibility of position and yaw simultaneously. To validate that our method is
practical and generic, we integrate it into a customized quadrotor tracking
system. The experimental results show that our visibility-aware planner
performs more robustly and observes targets better. In order to benefit related
researches, we release our code to the public.
