[talk-au] Mapping interchanges levels or turn restrictions

Roy Rankin rrankin at ihug.com.au
Mon Jan 11 11:29:57 GMT 2010


Oops,

I meant a east bound lane(s) going south crossing the west bound lane(s).


On 01/11/2010 09:44 PM, Roy Rankin wrote:
> 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
>
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