[OSM-talk] Turn restrictions

[Steve Coast]

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.

have fun,

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