[Routing] generalized routing format

[Philip Homburg]

In your letter dated Wed, 15 Oct 2008 23:45:46 +0200 you wrote:
>Marcus Wolschon wrote:
>> I think it would be better to discuss basic
>> storage and indexes first before going on
>> about special optimizations.
>>   
>I agree with that.
>Is there some lowest common denominator for a generalized routing format?
>Something everyone could use / need who works on routing osm data?
>There is a nice visual description by Michael Josenhans in the wiki
>http://wiki.openstreetmap.org/index.php/OSM_Routing_Data_Layer
>As a first step merge the intermediate nodes of degree two?
>Is this simple enough to fit everyone?

One thing worth considering for routing (not for displaying a moving map)
is the use of a line graph (http://en.wikipedia.org/wiki/Line_graph).
That should make it possible to represent turn restrictions directly in the
graph. And it also provides easy support for different costs of crossing
an intersection (a left turn compared to a right turn).