[OSM-talk] junction_ref=<whatever>

[matthew-osm at newtoncomputing.co.uk]

On Fri, Mar 16, 2007 at 04:36:31PM +0000, Richard Fairhurst wrote:
> David Earl wrote:
> 
> > I agree with you completely in principle, but we're not even close to having
> > the data structure to support this properly. We need superways or some such
> > to define junctions, to give us something to attach junction_ref to.
> 
> Would it be possible to have an extra tag to tie this "orphan"  
> junction_number node to the real ways?
> 
> I'm thinking of an extra node tag like  
> "associated_way=123519;123520;123521", which would imply that this  
> junction_number node describes a junction drawn as ways 123519,  
> 123520, and 123521 (maybe the roundabout and two slip roads  
> respectively).

Why not the following:

junction_ref on a node is a renderer hint only. I envisige the node being tagged

  ref = M1
  junction_ref = 23

and being placed near the junction itself. For a junction of two motorways, two
nodes would be placed nearby.

In addition, junction_ref on a way is for routing. Each way of motorway_link (or
*_link) at the junction would be tagged as junction_ref=<n>, too. For a standard
junction up to a roundabout this would be one tag on each of the presumably four
ways.

For a motorway_link between two motorways, I would split the way in to two and
place a junction_ref relevant to the connected motorway for each half.
Presumably this should already be the case anyway, as one half will be ref= one
motorway, and the other half would be ref= the other.

I am not convinced about putting junction_ref on the actual roundabout itself.
In this case the ref= tag would not be the ref for the motorway, and therefore
the junction_ref (which depends on ref) would be referring to the wrong road.

If that makes any sense?

Cheers,

-- 
Matthew