UAV altitude and attitude stabilisation using a coaxial stereo vision system

This study describes a novel, vision-based system for guidance of UAVs. The system uses two coaxially aligned cameras, each associated with a specially-shaped reflective surface, to obtain stereo information on the height above ground and the distances to potential obstacles. The camera-mirror system has the advantage that it remaps the world onto a cylindrical co-ordinate system that simplifies and speeds up range computations, and defines a collision-free cylinder through which the aircraft can pass without encountering obstacles. We describe an approach, using this vision system, in which the attitude and altitude of an aircraft can be controlled directly, making the system particularly suited to terrain following, obstacle avoidance, and landing. The autonomous guidance of an aircraft performing a terrain following task using the system is demonstrated in field tests.