[Tagging] Route members: ordered or not

Volker Schmidt voschix at gmail.com
Thu May 3 16:59:40 UTC 2018


@Colin:
You got me there: I implicitly excluded the possibility that a way may be
part of the route more than once.
I assumed this to be a general rule.
If you do not exclude it also the more than-than-two-ends exclusion rule
falls apart.
@Adrian:
What does RA do with routes where the same member appears several times?



On 3 May 2018 at 18:49, Colin Smale <colin.smale at xs4all.nl> wrote:

> Why does a loop make it impossible to sort the ways? It implies that a
> section of the route is present twice in the relation, but there is surely
> no distinction between the first traversal of a way and the second
> traversal?
>
>
>
> On 2018-05-03 18:42, Volker Schmidt wrote:
>
> I will try to explain this in a more systematic way:
>
> Routes belong to either of two categories:
> (A) Those whose members can be sorted into a single ordered sequence
> (B) Those that cannot be sorted into a single ordered sequence of members
> Sorting makes only sense for category (A)
> Routes of type (B) can be subdivided into routes of type (A), each of
> which can be sorted, but the overall route can not be sorted.
>
> Routes are of type (A) if
> (1) the path from begin to end is identical to the reverse path with  all
> members traversed in the reverse order and in the opposite direction
> or
> (2) all members have the role forward
> or
> (3) all members have the role backward
>
> Any route
> (1) that has more than two ends
> or
> (2) that contains any loop (except the case that the entire route is a
> single loop)
> or
> (3) that contains any element with role forword or role backward (except
> the cases of all-forward or all-backward)
> or
> (4) that contains node or area elements
> is of type B
>
> I am not sure if I have taken care of all cases - please complete as
> necessary
>
>
>
>
> _______________________________________________
> Tagging mailing list
> Tagging at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging
>
>
> _______________________________________________
> Tagging mailing list
> Tagging at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tagging/attachments/20180503/794676ba/attachment.html>


More information about the Tagging mailing list