[Openstreetmap] viaducts

[Lars Aronsson]

Alex Vieira wrote:

> http://www.openstreetmap.org/edit.html?lat=52.059009695368&lon=4.36880027481075&zoom=14
>
> The straight road does not connect to the other one, they pass 
> at different levels. Probably this question has been asked (and 
> answered) already before, sorry for that...

Wow!  I've never seen a 4-level viaduct.  I think there are only a 
handful of 3-level crossings in all of Sweden, one of them at 
Helsingborg is partially mapped in Open Street Map,
http://www.openstreetmap.org/index.html?lat=56.086&lon=12.781&zoom=13

The Open Street Map project is still in an early phase and the 
data model is very primitive, really only consisting of nodes 
(points) and line segments in 2-dimensional space.  There is an 
ongoing discussion on how to make this more advanced, but I 
personally think we need a lot more data before this makes any 
sense.  My own philosophy is that OSM is just a big prototype 
where we get all the experience for the next, real system.  And 
the same goes for the World Wide Web, Wikipedia, and Linux...

When I have a 1-level crossing, I put a node (a point) at the 
center and draw all line segments to that point, for a total of 
five points and four line segments:

          o
          |
          |
      o---o---o
          |
          |
          o


When I have a 2-level crossing, I don't put the point at the 
crossing, only four points at the periphery and two crossing line 
segments without connection.


-- 
  Lars Aronsson (lars at aronsson.se)
  Aronsson Datateknik - http://aronsson.se