![]() ![]() With this additional information itineraries can be computed very fast. The main idea is to do a preprocessing on the graph once, to speed up all following queries. This question has been an active area of research in the last years. The former seems to use prominent Boulevard de Sebastopol even though it's slightly out of the way.Įdit: Neither of these examples seem to work anymore, but both did at the time of the original post. Here's another violation of the triangle inequality that suggests (to me) that they use some kind of tiered approach: X-Z versus X-Y-Z. But maybe their walking directions optimize for another parameter, too? Contrary to the triangle inequality, sometimes Google Maps thinks that X-Z takes longer and is farther than using an intermediate point as in X-Y-Z. This question was motivated by finding quirks in online mapping directions. What algorithms are actually used in practice? Then directions for two far-away points will involve local directions to a key points, global directions to another key point, and then local directions again.) However, our data is very structured, and perhaps some kind of tiered approach might work? (For example, store precomputed directions between certain "key" points far apart, as well as some local directions. Luckily, heuristic algorithms like A* will probably work. Graph algorithms like Dijkstra's algorithm will not work because the graph is enormous. Sometimes these points will be close together (within one city) while sometimes they will be far apart (cross-country). I want to be able to quickly compute directions from one arbitrary point to another. But suppose the data were in a simpler format, say a very large directed graph with edge weights reflecting distances. I mean, they probably have real-world data in some form, certainly including distances but also perhaps things like driving speeds, presence of sidewalks, train schedules, etc. How do map providers (such as Google or Yahoo! Maps) suggest directions? ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |