  R2 is a novel online any-angle path planner that uses heuristic bug-based or
ray casting approaches to find optimal paths in 2D maps with non-convex,
polygonal obstacles. R2 is competitive to traditional free-space planners,
finding paths quickly if queries have direct line-of-sight. On large sparse
maps with few obstacle contours, which are likely to occur in practice, R2
outperforms free-space planners, and can be much faster than state-of-the-art
free-space expansion planner Anya. On maps with many contours, Anya performs
faster than R2. R2 is built on RayScan, introducing lazy-searches and a
source-pledge counter to find successors optimistically on contiguous contours.
The novel approach bypasses most successors on jagged contours to reduce
expensive line-of-sight checks, therefore requiring no pre-processing to be a
competitive online any-angle planner.
