[Talk-GB] Roundabout, ways and relationship policies

[Steve Hill]

On Wed, 22 Jul 2009, Nicholas Barnes wrote:

> Should, for example, the component ways making up the roundabout be
> grouped in their own "I'm a roundabout" relationship?

Do we need to be able to tell which ways are part of a roundabout anyway? 
I mean, on the ground a roundabout is just a one-way circular road with 
some other roads coming off it - there isn't really anything special about 
it that makes it a roundabout.

The only use of an explicit "I'm a roundabout" tag/relation that I can 
immediately think of is to make driving directions more human-readable 
(i.e. "At roundabout, take the 3rd exit").  In this case it may be better 
for the data user to use some heuristic, much as we do ourselves when we 
look at a piece of road.  e.g. If there is a closed (clockwise in 
the UK) one-way loop with a diameter of less than X metres then consider 
it a roundabout when generating human-readable driving directions.

Using this kind of heuristic would also have the advantage of setting an 
application-specific upper bound to the size of a roundabout - when 
roundabouts get beyond a certain size then it is probably better for 
sat-navs to go back to the usual "take the next left" driving directions 
instead of "take the 7th exit".

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence