This project marks the dead ends (in fact, all cut edges) on OpenStreetMap. See an example.
We want to wonder around, navigating with OpenStreetMap, and never need to go back along the same way. To see where not to go, we'd like to add special marking to all cut-edges on the road graph.
The project reads OSM XML, builds the road graph, finds cut edges and
adds a tag to them (currently <tag k="construction" v="cut-edge">).
Later, this XML can be rendered to show the map with cut edges marked.
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We could add own tag (like
<tag k="cut-edge" v="yes">), but the Mapnik will not understand it. So in order to render with Mapnik, some tag known to it must be (ab)used. -
It may sound good to split the way into alternating cutting and non-cutting parts, and tag the cutting parts. But splitting an existing way into new ways will break relations. So the first approach is to add new way for each cut edge. Give this way a fake
osm_id, which is large enough not to conflict with any other way, and put it on layer high enough (e.g. 5). -
Performance. For a town area of about 50.000 inhabitants, graph contains 67K nodes, 77K edges, and 12K cut edges located on 3K ways; processing took 11s. But area of 1M inhabitants, 400K nodes and 450K edges, graph construction takes 2 minutes, and then Python repeatedly segfaults in pygraph module (Intel Pentium 1.4GHz, 1G mem)
The code uses pygraph.algorithms module. In Ubuntu Linux, it is provided by python-pygraph package.
python markOSMbridges.py source.xml [> result.xml]