If collision free paths can be found on search graphs with few nodes and coarse resolutions, then traditional A* is fast. However, if such paths exist only on fine resolution graphs or at deeper levels of search hierarchies then A* is usually very slow. The paper studies two questions. First, when it is beneficial to use the plain A* instead of the method resembling an earlier hierarchical planner (Autere and Lehtinen, 1997). Second, which of the following two ways is better? Explore all the, nodes at a resolution i before exploring any nodes at finer resolutions or at deeper levels of the search hierarchy: i+1, i+2, ... . The other way is to explore nodes simultaneously at several finer resolutions (展开▼
