We explore a symmetry-based reformulation technique which can speed up optimal pathfinding on undirected uniform-cost grid maps by over 30 times. Our offline approach decomposes grid maps into a set of empty rectangles, removing from each all interior nodes and possibly some from along the perimeter. We then add macro-edges between selected pairs of remaining perimeter nodes to facilitate provably optimal traversal through each rectangle.  To further speed up search, we also develop a novel online pruning technique.  Our algorithm is fast, memory efficient and retains both optimality and completeness during search.
['Daniel Harabor', 'Adi Botea', 'Philip Kilby']
Path Symmetries in Undirected Uniform-Cost Grids