  For safe vision-based control applications, perception-related constraints
have to be satisfied in addition to other state constraints. In this paper, we
deal with the problem where a multirotor equipped with a camera needs to
maintain the visibility of a point of interest while tracking a reference given
by a high-level planner. We devise a method based on reference governor that,
differently from existing solutions, is able to enforce control-level
visibility constraints with theoretically assured feasibility. To this end, we
design a new type of reference governor for linear systems with polynomial
constraints which is capable of handling time-varying references. The proposed
solution is implemented online for the real-time multirotor control with
visibility constraints and validated with simulations and an actual hardware
experiment.
