[Routing] Getting A* to prefer Motorways

[hubert schmid]

Hi,

> Aren't we looking in a directed graph situation? I know this can
> increase the search space, but still it would solve the turning
> restriction issue.

A directed graph will not solve the problem completely. It 
reduces the possibilities of movement and the to- and from-
links of a node are separated, but there is no way to access
the from-link while searching. 

I think, it is a matter of testing. A route-search-algo, which
stores the last link and makes a turning-restriction-test at
every node will slow down the calculation. If there are just
a few turning restrictions compared with a lot of 'normal'
nodes, the iterative way could be faster for most of the
real routes.
 
Another possibility is to usage a directed graph and to expand 
every node to four nodes. I saw this in smaller applications
in the context of traffic simulation. With the four nodes
you can describe every possibility of movement with its 
own link.

     ^ 
   | |
<--*-*--
   |X|
 --*-*-->
   | |


> Currently in The Netherlands we are also considering routing on the
> railway. With a bit of luck the "Nederlandse Spoorwegen" (Dutch
> Railways) will be interested in hooking up.

I created a mixed graph with roads and railways for germany.
It is funny to look at the shortest path, jumping from road
to rail and back. There is only a problem to get a vehicle
to use this shortest path ;)

Hubert

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