Aerial Following of a Non-holonomic Mobile Robot subject to Velocity Fields: A Case Study for Autonomous Vehicles Surveillance

Surveillance is a major concern nowadays for the development of autonomous vehicles (AVs) technology, in particular during prototyping stage. However, it is unclear what an effective strategy is for aerial imagery with drones. On one hand, the dynamics of such autonomous vehicle is commonly subject to non-holonomic constraints, whose steering wheel is driven under the paradigm of look-ahead, i.e. users drive a car by looking forward, instead of minimizing the instantaneous position error as if navigating in a smooth velocity field. On the other hand, aerial footage is typically conducted with underactuated drones where admissible position trajectories are limited to a subset of paths.In this paper, a scheme for aerial visual servoing of a mobile ground robot tracking a smooth vector field is proposed. The scheme is based on structural properties and constraints of both systems, such as a non-holonomy, nonlinear dynamics and underactuation. The result is aerial surveillance of an autonomous vehicle mimicking how we drive a real vehicle by redefining locally smooth velocity field toward the next target through admissible paths. Experiments show the feasibility of the proposed scheme by controlling the quadrotor's underactuated positions (x,y) from the velocity field, the altitude z to facilitate a monocular camera, and yaw angle ψ to recover the direction of the field.