Reactive obstacle avoidance for Rotorcraft UAVs

We present a goal-directed 3D reactive obstacle avoidance algorithm specifically designed for Rotorcraft Unmanned Aerial Vehicles (RUAVs) that fly point-to-point type trajectories. The algorithm detects potential collisions within a cylindrical Safety Volume projected ahead of the UAV. This is done in a 3D occupancy map representation of the environment. An expanding elliptical search is performed to find an Escape Point; a waypoint which offers a collision free route past obstacles and towards a goal waypoint. An efficient occupied voxel checking technique is employed which approximates the Safety Volume by a series of spheres, and uses an approximate nearest neighbour search in a Bkd-tree representation of the occupied voxels. Tests show the algorithm can typically find an Escape Point in under 100 ms using onboard UAV processing for a cluttered environment with 20 000 occupied voxels. Successful collision avoidance results are presented from simulation experiments and from flights with an autonomous helicopter equipped with stereo and laser range sensors.