[OSM-talk] Turn restrictions ambiguity

[SteveC]

On 23 Apr 2009, at 12:17, Teemu Koskinen wrote:

> On Thu, 23 Apr 2009 21:34:05 +0300, SteveC <steve at asklater.com> wrote:
>
>> I don't see a clear explanation as to why there is ambiguity if you
>> don't do turn restrictions at the end of ways on the wiki. There is
>> some stuff in the talk page
>>
>> 	http://wiki.openstreetmap.org/wiki/Talk:Relation:restriction
>>
>> Anyone care to provide an explanation?
>>
>> The reason I ask is that I've come across some roads where there is a
>> restriction every  other turn in both directions... and splitting a
>> mile long road in to 30 pieces seems nuts. As a follow up, I can
>> guess, but what will the renderer do in that situation? I'm guessing
>> mapnik will give up trying to put 30 names on a one mile road and
>> won't notice they're the same name?
>
>
> If both from and to ways continue after the via point and neither is  
> one-way, there's two possible ways to interpret it: the restriction  
> could apply when coming from either of the ends of the from-way.  
> This of course doesn't matter if there is similar restriction coming  
> from both directions, but that's not nearly always the case. And  
> even if there is symmetry in the real life restrictions, it's not  
> appropriate in my opinion to map those with just one restriction.

eh? don't you assign direction by saying 'from' and 'to' ?

>
> About the splitting, it's already necessary to split the way if some  
> other property changes, eg. speed limit or number of lanes (which  
> does change more often in some places than there are restrictions),  
> it's either the renderer's job to figure out that the pieces belong  
> together or we could use some relation to group the pieces together  
> but that too would require support from the renderers.

Yes - but turn restriction splitting will lead to much, much more splits


>
>
>> Best
>>
>> Steve
>
>
> Regards Teemu Koskinen
>

Best

Steve