Hi Y'all,
I am trying to build an algorithm to produce correctly layered,
correctly connected road networks from OSM ways + the layer tag.
There are a few "easy" cases:
- When two ways cross laterally but have different layers and have no
node at the intersection, clearly they do not connect in space, and the
layer of each of the four partial ways at the intersection point is clear.
- When two (and only two) ways end at a common node, and the ways have
different layers, it's probably a safe bet to say that this is where the
layers transition and the two ways should connect. (E.g. a way with
layer=1 and a way with layer=0 form a highway that has a bridge...this
junction is where the bridge "hits the ground".
There are two cases I am wondering about though:
- Two ways cross and have different layers, but a common node exists at
the crossing point.
- Three ways come together, two of one layer, and one of another layer.
An example of this last case might be a residential road that is about
to "bridge" over a highway, but the bridge ends at a T junction to
another residential road, e.g.
----*=====
|
(Sorry for the ASCII drawing...)
These two cases seem tricky to me because there may be some cases where
ways of different layer need to be brought together and some where they
need to be kept separate.
Does anyone have thoughts (or has anyone implemented) a heuristic to
decide when two ways need to be put into the same layer at a given node?
Thanks!
Ben
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