
Show HN: Eppstein’s k shortest paths in the web browser with OpenStreetMap - ctcliff
https://christophercliff.com/eppstein/
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antoniomedrano
This demo is useful in showing how useless KSP is for finding meaningful
alternate routes. Basically, brute force enumeration requires generating
massive numbers of paths before you get anything with any sort of spatial
differentiation. Until then, all you get are tiny variations on the shortest
path. Other methods are much more effective at finding locally optimal
spatially diverse alternate routes with much much less effort. Gateway
shortest paths are one such example.

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ctcliff
Yeah, that was an unpleasant surprise when I started plugging in the street
map data :D

I'm experimenting with other algorithms and will post some (hopefully) more
interesting results soon.

~~~
danpat
A plug for one of my co-workers who recently finished his PhD on alternative
route finding:

[http://algo2.iti.kit.edu/documents/Dissertation_Kobitzsch_Mo...](http://algo2.iti.kit.edu/documents/Dissertation_Kobitzsch_Moritz.pdf)

Choice quote from page 50:

 _k-Shortest Path. A, at the first glance reasonable, approach to alternative
routes is the k-shortest path problem [Yen71]. The basic notion behind the
problem, which has been studied quite extensively (e.g. [Shi79, Epp94, Epp98,
Rup97]), is that next to the shortest path itself, slightly suboptimal paths
will offer good alternatives. While this idea seems valid for specific
networks2, it has been described as less effective [BDGS11] in the context of
alternative routes in road networks. It is rather unlikely to find a good
alternative route among the first few hundred paths. Jumping off the highway
at a ramp and directly returning back onto it does not take much time compared
to the full journey. Doing this at every possible combination of ramps might
already contribute a large number of possible paths that are only slightly
worse than the original shortest path. This directly implies that we might
need a very large value for k before we can report a reasonable alternative
route._

