[Routing] generalized routing format - comments on degree 2

[Marcus Wolschon]

On Mon, 20 Oct 2008 05:28:02 -0700, "Tristram Gräbener"
<tristramg at gmail.com> wrote:
> Hello,
> 
> After some thoughts, I think that what I would need, is only the
> current xml files, where there is a constraint that each way may be
> only made of nodes of degree 2 (except  at start and end). Of course I
> guess that there is no way to change the API ;)
> 
> Wouldn't be it easy to make that as the exchange format, e.g. by
> adding a Link property made of nodes ? Of course this would break the
> normal form as it would be redundant to ways.

I think the issue is a bit more complicated then this.
* Not all ways are roads. You can have nodes that are of a
  degree > 2 only because they are also used by a passing
  river or similar.
* Before reducing roads to links between intersections you need
  to compute your metrics. You loose all information about the
  length and path of the road.
* This really means _your_ metrics. Others may want to add a penalty
  for curvy mountian-roads in addition to their length+highway-class
  or they may compute for a truck instead of a sports-car.

Thus you can do some routing on a graph reduced as proposed
by you but you will not be able to compute the shortest, nor
the fastest route as you will have lost that information in
the export.

> A universal binary format with some API would be nice for people that
> want to play with graph algorithms (like students) but I personnaly
> have no use for that (yet).

Well, you don't have to.
I have no need for many other features, so
I let them be and don't care about them.
>