[OSM-talk] oneway=1

[Chris Fleming]

Arieh Skliarouk wrote:
> Hello,
>
> I think it is wrong to specify street direction explicitly, at least
> for the long term. Street direction tend to change, and you don't want
> OSM users to get tickets for going wrong way?
>   
Well people can still read roadsigns....

If you look at the commercial mapping providers then you will see that 
this is something that they frequently get wrong. Just try using satnav 
to navigate around Glasgow's one way systems for example.

Catching changes is something a big community of mappers will be able to 
spot and change very quickly.

> I am sure commercial mapping companies have some kind of agreement
> with authorities regarding directions change. Until OSM has something
> similar, we can't rely on this information to remain static.
>
> Direction tags on roads wider than certain width, can be relied upon,
> though. For narrow streets the direction needs to do deducted
> statistically.
>
> I see following algorithm as one that can work:
>
> Initially, mark all narrow streets as having "questionable" direction,
> with allowed direction of the one that submitter have travelled on it.
>   
If both directions are permitted and used then this is a two way street, 
if only one direction is permitted (and used) then it's a two way 
street. I'm not sure how this can be questionable?

Surely it would be better to tag the street as "narrow" only use for 
access? or similar?

> The client software (one that runs on PDA) needs to be able to notify
> server that the car just passed the street in previously
> known-forbidden direction. Once several similar-looking GPS-traces
> from different users are received by server, the street direction can
> be recalculated.
>
> Similar way, server should deduct streets that have not seen certain
> direction GPS-traces and mark the street as "questionable" direction.
> PDA-client should notify the user about questionable status of the
> street direction and allow clarification of the data by user, with
> subsequent upload to the server.
>   
Surely it's better that someone does this manually, rather than trying 
to deduce this from traces?

> Other factors that can change in lifetime of a street (off the top of my head):
> * Whether only public transport is allowed
> * Trucks are allowed only during certain hours
> * Cars with dangerous cargo (explosives, fuel, etc) are not allowed
> * road is under (re)construction, find another route
> * Only certain maximum weight or height vehicles are allowed through
> * Pedestrian only
> * etc
>
> What do you think?
>   
 Yes. But these things don't tend to change that often? A big community 
of local mappers (or even just users who notify mappers?) would catch 
these very quickly, probably much quicker that the mapping companies, 
who often get these things wrong anyway. For example the recently opened 
M9 Spur on google is almost right: 
http://maps.google.co.uk/maps?f=q&hl=en&geocode=&q=EH30&ie=UTF8&ll=55.973318,-3.399582&spn=0.040104,0.088491&z=14&om=1

But the new road is Motorway (M9 Spur) not  the A8000. The A8000 is now 
the B800! On OSM it's correct (we also have all the roads crossing at 
the right layers):
http://www.informationfreeway.org/?lat=55.975530134242675&lon=-3.390307315041101&zoom=14&layers=0000F0B0

I know of dozens more examples where commercial maps have not updated to 
take changes into account, but OSM has...

Cheers
Chris

-- 
http://www.chrisfleming.org/