With the resolution and newness of Nearmap images Freeway/Motorway interchanges are being mapped in detail rather than schematically. This brings up the issue on how to best do this.
Picture this case. A freeway goes north-south and a dual lane east-west road goes over the freeway with a connection to the freeway. West bound traffic on the road going onto the freeway heading south must cross the east bound traffic on the road. Both these ways are oneway. I see two possible ways to map the lane(s) turning south and the lane(s) going east. 1> The ways cross with a common node and a no_right_turn or only_straight_on restriction. (both lane(s) must be broken into two ways at the common node as required by relations) 2> The ways cross without a common node but are on different layers. (Although physically using the same pavement where they cross). With freeway over/under road and 4 on/off ramps, 4 layers are required. To me the second method is the simplest although I usually think of different layers as having different elevations. The reason for this e-mail is I see no discussion of this in the OSM documentation, but OSM will be easier to maintain if similar situations tend to be mapped in similar ways. The following anecdote describes my experience today. Today I came across some issues with the turn restrictions on the interchange between Falcon Street and the Gore Freeway in North Sydney. (http://www.openstreetmap.org/?lat=-33.82907&lon=151.21494&zoom=17&layers=0B00FTF ) The mapper did not realise that ways with turn restrictions must break at the via node. Unfortunately the current tested JOSM does not handle turn restriction relations properly when a way is split and much effort is required to fix up the relations after a way split. As each way had quite a few turn restrictions I realized that after splitting the ways it would require some time to sort out the relations. I thus used method 2 above and deleted all the relations. Regards, Roy Rankin _______________________________________________ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au
