[OSM-talk] How to integrate a roundabout into a relation

[Lester Caine]

Marc Schütz wrote:
> Am Samstag 31 Januar 2009 10:32:04 schrieb Peter Vitt:
>> Hello List,
>>
>> On talk-de we had a discussion about relations, especially routes, and
>> roundabouts the other day.
>>
>> The topic was: How to integrate a roundabout into a relation.
>>
>> For now we have three different approaches:
>> 1) Leave the roundabout untouched (closed way) and integrate it completely
>> into the relation.
>> 2) Leave the relation untouched (closed way) and _don't_ integrate it into
>> the relation.
>> 3) Split the roundabout as needed, integrate all parts of it into a
>> dedicated roundabout-relation and only the needed parts into the route.
> 
> 4) Split the roundabout as needed, tag all parts as junction=roundabout (don't 
> use a roundabout relation), and add only the needed parts into the route.

5) Properly define a relation so that it does not need to know every
single segment, but can 'work it out' from the normal rules. That is it
only needs to pick up segments from the roundabout that fill in the gap
on the segments it is following. So going north on a dual carriageway,
only the north facing segments are traced, along with the correctly
directed segments in the roundabout. A complex motorway interchange may
have non-closed sections related to a roundabout junction, but if the
routing does not require accessing the actual roundabout then it's
segments will be skipped - but it still has to be part of the route
relationship since one needs to know where you can join or exit the route?

-- 
Lester Caine - G8HFL
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