Take live traffic conditions into account

[quintona]

Add the capability to calculate routes based on a current understanding of road speeds based on live traffic conditions. This would need to include the capability to initialize the graph with known speeds (attained via some data source or via estimate) and then update it later based on changing conditions. The key intentions being that when major conditions exist and the road speeds drop to near zero, that different routes are selected, and in all cases that realistic time estimates are provided for the route based current conditions.

[karussell]

Using live traffic for the normal graph is easy: just apply the different speed conditions to the edge:

someEdgeIterator.flags(carFlagEncoder.flags(speed, direction))

For a contraction hierarchies algorithm (the faster one) this is not possible.

[quintona]

When you say it isn't possible, you mean it isn't implemented or it simply isn't possible? You will excuse the ignorance on the contraction hierarchies.

[karussell]

IMO it is not possible for CH: http://algo2.iti.kit.edu/download/dtch.pdf

So, you can rebuild the hierarchy after a change. If this rebuilding is fast enough then of course it is possible in practise. (BTW: for mobile devices this CH rebuild stage is NOT possible at all due to the heavy resource utilization!).

Besides all this, the CH preparation in graphhopper is very slow at the moment and could need some improvements like parallelization etc. And there are other fast algorithms where a custom metric is better recognized, see http://research.microsoft.com/apps/pubs/default.aspx?id=145688

[quintona]

I would prefer to go the route of the rebuild. How/where should I set the speed for a given OSM way when doing the graph build?

[karussell]

See e.g. CarFlagEncoder.SPEED

[karussell]

I do not expect open or free sources for traffic conditions, so we won't be able to create any specifics for this. Reopen if you have an idea what could be improved.