[OSM-talk] Turn restrictions

Steve Coast steve at asklater.com
Thu Aug 16 10:58:53 BST 2007

On 16 Aug 2007, at 10:29, David Earl wrote:

> 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/

Yes but my way is about a billion times simpler, human readable and  
works today. :-)

have fun,

SteveC | steve at asklater.com | http://www.asklater.com/steve/

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