Hi all, I've been needing to use geobase2osm in a project of mine (not directly related to the geobase import), and noticed (as other people have) that it's generating a lot of duplicated nodes. Aside from being unclean and wasteful, this makes the generated osm file non-routable. Well, today I decided to do something about it. Looking at the source, I noticed quite a bit of complicated code to "merge" identical OSM nodes at junctions (trusting geobase to provide the right hints of where junctions are). Evidently this wasn't working quite as expected.
I decided to try something simpler: just keep a hashtable of node "keys" (latitude and longitude) as you go along, and reuse nodes that have occurred before. :) At first glance, this approach seems to work fairly well. It seems intuitively "right" to me that if two ways have a common lat/lng point in common, they should be connected. A quick count of running the two algorithms on Edmonton, Alberta, reveals that where the old script resulted in 77242 (!) overlapping nodes (sometimes up to 8 on a single lat/lng position!), my code resulted in 0. Incidentally, this technique (if it's a good one) could be applied in automatic fashion on existing portions of the geobase import, eliminating the need for tedious manual work. Anyway, I don't have commit access to the OpenStreetMap subversion repository holding geobase2osm, so I decided to fork the repository using git and put up the result here: http://github.com/wlach/geobase2osm Oh, I also patched it up to not do coordinate transforms between the NAD83 and WGS84 systems, as apparently (http://sci.tech-archive.net/Archive/sci.geo.satellite-nav/2006-09/msg00307.html) there is no difference when it comes to positioning. Empirically, this seems to be true: the output without this transform seems 100% fine. Dropping these transforms allows us to drop the osgeo dependancy, which makes the whole thing run on OpenSUSE in the first place. More exciting geobase2osm work coming later. Maybe. Questions/comments? Let me know! -- William Lachance [email protected] _______________________________________________ Talk-ca mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk-ca
