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

I think it's worth to work-out your idea with "quadrants". More strictly, I'd call it a low-resolution route search.

You may pick X connected nodes that are close enough, and treat them as a single low-resolution node. Divide your whole graph into such groups, and you get a low-resolution graph. This is a preparation stage.

In order to compute a route from source to target, first identify the low-res nodes they belong to, and find the low-resolution route. Then improve your result by finding the route on high-resolution graph, however restricting the algorithm only to nodes that belong to hte low-resolution nodes of the low-resolution route (optionally you may also consider neighbor low-resolution nodes up to some depth).

This may also be generalized to multiple resolutions, not just high/low.

At the end you should get a route that is close enough to optimal. It's locally optimal, but may be somewhat worse than optimal globally by some extent, which depends on the resolution jump (i.e. the approximation you make when a group of nodes is defined as a single node).