[OSM-dev] Simplifying data for routing

[Frederik Ramm]

Hi,

> OK. So in the case of more than 4-way intersections, or intersections  
> added later, are mapping programs/map editors smart enough to use pre- 
> existing nodes?

That's done manually by the person entering the roads. They will either 
connect their segments to an existing node or insert a node into an 
existing segment.

> So I wouldn't have, say, three separate nodes in an  
> intersection?

If that intersection is topologically "one" intersection, having three 
nodes would be considered an error.

> How might I go about determining whether a node is an intersection?  
> The only solution I can think of is to track whether a given node is  
> referenced from two different ways. 

 From two different _segments_ at the moment, yes.

> Is that reliable?

Yes. There are of course some problems where people meant to create an 
intersection and forgot to put the node, but that should be none of your 
concern - if there is an intersection, there must be a shared node, and 
otherwise it is an error. The Validator plugin for JOSM already alerts 
people to cases where two segments intersect without a node *and* 
without any of the ways having been assigned a different layer (bridge, 
tunnel etc).

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'