[OSM-talk] Turn restrictions

Robert (Jamie) Munro rjmunro at arjam.net
Thu Aug 16 12:28:32 BST 2007

Hash: SHA1

Steve Coast wrote:
> 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. :-)

Frederik's system "works today" and solves a whole bunch of other
possible issues where relationships would be useful. Human readability
is less important than machine readability. We can always convert
machine readable to human readable with a converter. The other way round
often requires a human.

Can we put Frederik's codebase on http://dev.openstreetmap.org/ (note
NOT http://dev.openstreetmap.org/~frederik/ or something), and declare
it OpenStreetMap 0.5 beta, ready for everyone to test.

Unless there are serious problems with Frederik's approach, we should
move to implementing it as soon as possible.

Robert (Jamie) Munro

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