[Routing] Errors in map data that affect correct routing - andwhat to do about it...

[Wolfgang W. Wasserburger]

> Hi Cathy,
>
> once I've been to Edinburgh, came by ferry and car to explore the
> northern coast of Scotland. That was a nice time. Now I have a
> wife, a house and a child leaving not much possibility for such
> travel. But luckily I can do other things :-)
>
> I think I can help you a bit. 1st I think that these double nodes
> are errors. Done by whatever version of whatever program. I think
> you can not prevent all errors. I think the API should reject
> those ways. However, now they are there. JOSM now has a good
> validator plugin. But it's a plugin, has to be installed
> deliberately and has not been there all the time.
>
> I will write a check program for these which we can use to
> identify those ways. Not a big deal. Should be done today or
> tomorrow. But then they will only be identified, not corrected.
>
> I just know about problems in routing, I don't actually "route"
> myself. I am the "checker". :-)
>
> One other thing. I think the OSM data/graph should be simplified
> to save ressources when routing. I could imagine a simplifier
> eliminating those nodes and those that are not the end of a road
> and don't connect to anything else. Of course the weight/length
> of the original path should be maintained.
>
In anyway for routing purposes you have to do a preprocessing:
1.) break all ways at crossings with other ways, because the OSM data model
allows ways across corssings
2.) calculate the length (or weight if you think about different speeds)
3.) there are various things taged to ways or even nodes, which could be
senseful for routing.

For my routing model I create tables where only the first and last node, the
weight and the id are saved.

Maybe I'm a purist on that point of view, but I do routing for logistics not
for public use, so it needs not to look nice, but it has to work.

Therefore also some Mappers work for nothing, because their tags cannot be
used, but it seems to be a kind of a hobby, not only a sensful work.

cheers from Vienna

Wolfgang