Fast Nearest Neighbor Search in SE(3) for Sampling-Based Motion Planning

Nearest neighbor searching is a fundamental building block of most sampling-based motion planners. We present a novel method for fast exact nearest neighbor searching in SE(3)—the 6 dimensional space that represents rotations and translations in 3 dimensions. SE(3) is commonly used when planning the motions of rigid body robots. Our approach starts by projecting a 4-dimensional cube onto the 3-sphere that is created by the unit quaternion representation of rotations in the rotational group SO(3). We then use 4 kd-trees to efficiently partition the projected faces (and their negatives). We propose efficient methods to handle the recursion pruning checks that arise with this kd-tree splitting approach, discuss splitting strategies that support dynamic data sets, and extend this approach to SE(3) by incorporating translations. We integrate our approach into RRT and RRT* and demonstrate the fast performance and efficient scaling of our nearest neighbor search as the tree size increases.