[Routing] How to Establish Road Hierarchy

[Dennis Luxen]

> > Very unlikely that A* beats CH in general.
> It certainly doesn't.
> 
> 
> A* is just so much more flexible. For example, you can add a new vehicle type without any significant penalty in terms of preprocessing. Or avoid traffic jams that change frequently. And the flexibility can result in significant savings on fuel and time.

I grant A* that it does not require any special preprocessing. I also grant that CH is not the answer to all questions.

Avoiding traffic jams is a much more delicate topic, because the naive method of adding a penalty and recomputing a new path usually fails. Also, you want to have some guarantee on alternative path quality and also on runtime. A* does not guarantee anything.

> Furthermore, as computers get cheaper and devices get faster, the difference in speed between A* and CH is becoming insignificant.

Plain wrong. A* does not scale.

> All these tradeoffs are firmly in favour of A* for most applications.

Also wrong. Especially in applications you want to have small search spaces and also compute many (sub-)paths.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/routing/attachments/20121212/95fd86a8/attachment.html>