[OSM-talk] Turn restrictions

David Earl david at frankieandshadow.com
Thu Aug 16 10:29:51 BST 2007

On 15/08/2007 22:48, Steve Coast wrote:
> So I'm on a train otherwise I'd link to Andys wiki page he pointed to  
> today, but I want to try out a turn restrictions scheme,
> Given a road direction, and roads 'Baker Street' and 'Marylebone  
> Road' you tag the way 'Baker Street' with
> no_turn_left:'Marylebone Road'
> If you can't turn right then it's 'no_turn_right'. If you can't turn  
> at all it's 'no_turn'. And thats it. There are three major problems  
> with this
> First, as far as I know JOSM doesn't let you use keys more than once  
> but the API does. So you can't have more than one no_turn_left. So  
> fix JOSM.
> Second, what if it's no turn for car but ok for bikes, or whatever.  
> Well, then shouldn't we look at triple tags?  
> car:no_turn_left:Marylebone Road ? That is, keyvals now have third  
> string along with key and val? We'd add a third keyval property, call  
> it what you will, and all the current keyvals will have that third  
> proprty set to 'general'. So general:name:Foo Street and so on. Then,  
> this third column can be specialised along the lines of Map Features  
> as the keys and vals are.
> Third, what if someone misspells 'Marylebone Road' or the road isn't  
> joined, or it doesn't exist or something. Well, people will enter bad  
> data ON PURPOSE and our map data will never be perfect ANYWAY. And,  
> it's a wiki so you can fix it. And, it's incredibly simple compared  
> with any competing scheme I've seen. Also, JOSM (or potlatch) can  
> prompt you and say 'ah-ha Mr. Mapper, that looks wrong!' And you can  
> read it, but you can't read bigscheme:way:324543525234:no_turn:34523452.

Frederick's prototype for relationships addresses this properly, by 
grouping the Ways affected by reference rather than name.

See http://openstreetmap.gryph.de/entities/


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