[OSM-talk] Ways on bus route relations

[Eduardo Habkost]

On Sun, Jun 15, 2008 at 08:53:53PM +0200, Frederik Ramm wrote:
> Hi,
>
>> Do the "ways making up the route" (as defined on Relations/Routes
>> proposal) must be actual highway-tagged ways
>
> Yes.
>
>> or they may be distinct
>> (maybe untagged) ways drawn over the highway ways?
>
> To re-use a popular exclamation of the last few weeks: "Ye gawds no!" ;-)

Okay.  :)

>
>> I am asking that because on some streets there may be many different bus
>> routes going through it with different entry/exit points. If the ways
>> making up the bus route must be the actual highway ways, those streets
>> will need to be splitted on many tiny little ways, so that each section
>> will belong to a different set of route relations. Did I understand it
>> correctly?
>
> Yes. This is somewhat of a shortcoming but that's the way it is currently 
> done.

This doesn't seem to be a problem only when making bus relations:
streets with lots of tunnels or bridges need to be splitted also. So,
it is a more general issue. I will try to live with it, by now.  :)

>
[...]
>
> Or you simply ignore the fact that the bus route does not use the full 
> length of the way; it would still be possible algorithmically to find out 
> which part of the way the route uses (except from circular road layouts). 
> Won't look nice on today's renderers but who says they cannot be improved?

That is an interesting idea: maybe I can do this to enter data about
the bus routes more easily and later algorithmically split the ways on
the right places.

>
> A third option would be inventing a special kind of relation that's called 
> a "way section"; it would contain the start node, end node, and way and 
> model that part of the way that lies between the two nodes. Then make your 
> bus route relation use these way sections as members wherever the bus route 
> doesn't use the full way. But this would also be something new and not yet 
> supported by renderers.

I have seen two proposals that would handle the current cases of massive
splitting: "tag section" relations (similar to what you mentioned
above)[1] and "collected ways"[2]. Both seem to sove the same problem
using different approaches.

At first I thought the collected-ways approach to be better and more
intuitive, but the way-section approach now seems to be better, the more
I think about it.

(The collected-ways proposal may be useful on other cases, but I
was thinking about the cases of splitting due to bridges/tunnels and
bus routes, only)

[1] http://wiki.openstreetmap.org/index.php/Relations/Proposed/Segmented_Tag
[2] http://wiki.openstreetmap.org/index.php/Relations/Proposed/Collected_Ways

-- 
Eduardo