A* Algorithm for very large graphs, any thoughts on caching shortcuts?

Question

I\'m writing a courier/logistics simulation on OpenStreetMap maps and have realised that the basic A* algorithm as pictured below is not going to be fast enough for large maps (

Answer 1

There are specialist algorithms for this problem that do a lot of pre-computation. From memory, the pre-computation adds information to the graph that A* uses to produce a much more accurate heuristic than straight line distance. Wikipedia gives the names of a number of methods at http://en.wikipedia.org/wiki/Shortest_path_problem#Road_networks and says that Hub Labelling is the leader. A quick search on this turns up http://research.microsoft.com/pubs/142356/HL-TR.pdf. An older one, using A*, is at http://research.microsoft.com/pubs/64505/goldberg-sp-wea07.pdf.

Do you really need to use Haversine? To cover London, I would have thought you could have assumed a flat earth and used Pythagoras, or stored the length of each link in the graph.