On 2/25/2013 10:42 PM, Elliott Plack wrote:
On the wiki for the public transport routes, it says not to use the roles,
so that is what I'd been doing. Here is a link, 2nd paragraph under route
direction:
http://wiki.openstreetmap.org/wiki/Proposed_features/Public_Transport#Route
I suppose this schema emphasizes multiple relations for each route, forward
and backward. I'd like to know more though if you're seeing other mappers
use those roles on public transport mapping.
-Elliott
I find that the best path in OSM is hard to find when there are many
sources of information. I see now that the JOSM link points to the
proposed_features page, which in turn points to other pages since it is
now "approved", for what that is worth.
As I understand it, the original historical relation method would use
a single relation path for a classic bus out+back trip, with roles of
'forward', 'backward', and 'alternate' to indicate the bus direction.
The 'alternate' case did not really facilitate being able to describe
the entire bus path for all possible cases. With the new
public_transport proposal, they wanted to drop the 'alternate' role, as
well as including the same ways more than once in order to trace a path.
My impression is that they took it a step further and recommended no
roles for ways, relying on the editor instead to create members in order
of traversal.
Relying on the editors to maintain member sorting can still
frequently fail: I found that the way sort order was frequently lost
while I was working with them - I used the JOSM Public Transport plugin
to automatically sort them again. I never found exactly which
operation disturbed the sort order. The Public Transport plugin will
also automatically assign roles. The Public Transport plugin has a few
quirks though, so I'm not sure how widely it is used.
My opinion - it looks like the 'forward' and 'backward' roles are
popular for bus route relations. And they allow for arrows on the
map rendering. On the plus side, JOSM can sort them and has a visual
indicator in the relation editor for connectivity when they have forward
and backward roles. But it is also easy to visually check the complete
relation path by just highlighting the relation in JOSM. I'm not sure
if GO-SYNC recommends the use of roles when it compares OSM to GTFS routes.
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