[Routing] generalized routing format

[Robert (Jamie) Munro]

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flo Detig wrote:
> 
> ps: some random thoughts:
> What about even more layers?
> In case of greedy (dijkstra-/a*-style) BFS you could start 'searching'
> until the first higher-layer-node appears, for instance a 
> residential-junction.
> After that stay on that layer and only examine 'arcs' to other junctions
> until you reach the first 'secondary-layer-junction', after which you 
> can ignore
> junctions to residential (lower-level) streets and move on in bigger steps.
> Once you arrive at the motorway-level you search on that layer / graph
> that solely consists of arcs between 'motorway-junctions' (german 
> Autobahnkreuz)..
> (could be implemented by adding an integer for layer to the nodes table
> and computing shortest paths between neighbouring nodes in each layer
> resulting in a edges-/arcs-/pgrouting-table with source-target-cost)
> But how get 'down' again to find the final destination node?
> 
> Please excuse if this sounds stupid. I'm just loud thinking..
> Probably this is this too complicated.
> Any opinions?

As said in another post, it might work if combined with a Bidirectional
search(*), but you'd have to be careful with what you put in each layer.
For example, a small A road that worked as a short-cut between 2
motorways would probably have to be on the motorway layer, otherwise you
might find yourself having to traverse a large section of the motorway
network to find your way around.

For example, you don't want to go all the way around the M25 to get from
Dartford to Thurrock, you want to take the A282 over the Dartford
Crossing (which links the 2 ends of the almost circular motorway)
http://www.openstreetmap.org/?lat=51.4718&lon=0.2514&zoom=12&layers=B000FTF

Robert (Jamie) Munro

* http://en.wikipedia.org/wiki/Bidirectional_search
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