[OSM-dev] Proposal: Make relations ordered

[Frederik Ramm]

Hi,

> To be honest the thought of relations getting ordering fills me with
> dread. Potlatch is only just about to get relations support (thanks
> entirely to Dave Stubbs) in 0.8; the thought of having to redesign it
> and add a load of crap to handle splitting/merging/whatever doesn't
> exactly fill me with joy.

I don't think there is a connection between the problem of splitting  
and merging ways that are members of relation, and ordering. The  
former is a problem that you have to deal with, one way or another,  
anyway; the way you do it might be marginally different if you have  
to look at ordering but really not much.

> Similarly I don't see why Frederik's initial ribbon-like loop
> (http://lists.openstreetmap.org/pipermail/dev/2008-March/009389.html)
> needs to be solved by ordering.

Assume the relation controls your bus. The bus needs to know where it  
is supposed to go. You have to have a way to describe this.

> One of the most frequently cited use
> cases for relations is turn restrictions. Surely this is nothing more
> than a non-mandatory turn restriction?

In this case, the idea was that the intersection is theoretically  
unrestricted, you just want a way to describe the route the bus  
takes. Turn restrictions don't help you there. - One example people  
were mentioning is bus stops; they want to make the bus stops members  
of the relation, and they want to be able to print them out in the  
correct sequence. What they can do, today, is have the membes in the  
roles "stop01" to "stop99" and achieve ordering through that. However  
this makes generic editor support even more difficult than it alreay  
is...

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'