[OSM-talk] lanes

[Karl Newman]

On Sun, Oct 12, 2008 at 9:13 AM, Gervase Markham <gerv-gmane at gerv.net>wrote:

> graham wrote:
> > - Say I have a bus lane (or cycle lane) running along one side of a
> > two-way road (the most common situation where I am).   Just attaching a
> > 'left' tag to it makes it dependent on nobody ever reversing the
> > arbitrary direction attached to the way.
>
> No, it doesn't, because editors would make flipping the left/right part
> of the "reverse way" command, just as they now flip "oneway"s and so on.
> There are various consistency checks editors need to do when making
> changes - this is just another one.
>
> > - More serious, I think: it just feels quite arbitrary as a solution: I
> > would have to tag a lane as being 'left' in relation to the random
> > direction the arrows on the way happen to be pointing, rather than in
> > relation to anything in the real world.
>
> How else do you unambiguously intrinsically define the side of a way?
> Unless it's a closed way, where you have "inside" and "outside", the
> only way is to give it a direction (which it has) and say "right" or
> "left".
>
> You can define it extrinsically using things like "north" or "west" but
> that runs into problems with roads which curve, or even run in a circle.
>
> > 2. have an 'origin' tag to be used on the first node of a way
> > independent of direction; if the way direction flipped, the origin would
> > stay in place. 'Left' or 'right' would be in relation to the origin
> > node. Still completely arbitrary where the origin goes, and how do you
> > find it on a long way?
>
> If my proposal has disadvantages, then this has them all but adds some
> new ones too :-)
>
> > 3. Make more of a separation between internal representation of ways and
> > user views in josm/potlatch. All ways have a direction which is
> > independent of the 'arrowed' direction which can be displayed to users,
> > and is fixed - a totally arbitrary value used only as a fixed reference.
>
> Why? Why not just use the arrowed direction? After all, it's not exactly
> complicated to flip tags when you change the direction of the way.
> That's why the scheme is generic :left and :right - so it can be used on
> any tags.
>
> Gerv
>

Just as a note, someone already added automatic left/right tag changing to
JOSM when a way is reversed. It works for a few different schemes, including
:left and :right.

Karl
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