[OSM-talk] How do I tag this road in OSM

[Etienne]

Christoph
See my comments below.  There was a thread a while back about this.  I put
forward some arguments about the fact that segments are not really needed.

I'd really like someone to highlight why segments are actually necessary.  I
believe that ways with an ordered list of nodes would do the same job.  I
must be missing something but no one has yet been able to explain what I am
missing.  I hoped that Steve would enlighten me, but he was away at the time
of the earlier thread and didn't pick up on it.  Maybe he'll chip in now
(Steve?).

Etienne


On 8/1/06, Christoph Burghardt <Christoph.Burghardt at uni-rostock.de> wrote:
>
> >
> > You might want to think about it the other way round.  Segments are the
> > redundant element.  All they provide is information about the direction
> > between two nodes.  Ways can the thought of as multi-segmented paths.
>
> Mmh - this approach has some significant disadvantages for me:
>
> 1.) First i set the points, then i connect the segments, after that i
> generate a way. How should i construct a way without these prior
> informations?


This is how you would do it (using a hypothetical editor that is a bit like
JOSM):
1. Select way drawing mode.
2. Position the cursor at the start of the way and click
3. Move the cursor to the next point on the way and click
4. Repeat until done.
5. Add tags to the way.

This is how it is currently done with segments (using JOSM):
1. Select node drawing mode
2. Position the cursor at the start of the way and click
3. Move the cursor to the next point on the way and click
4. Repeat until done.
5. Select segment drawing mode
6. Position the cursor at the first node and click
7. Drag the cursor to the next node and release
8. Repeat until done
9. Select way drawing mode
10. Position the cursor on the first segment and click
11. Position the cursor on the next node and click
12. Repeat until done.
13. Add tags to the way.

I think first way is simpler but you may be more comfortable doing it the
second, more familiar way.


Until now a segment is the basis for a way, you can't remove it!
> agree with you, ways are collection of segments. but you will always need
> the segments as a base.
>
> 2.) If one tag changes (i.e. class, highway, speedlimit) you have to
> generate a second way. In the worst case you have as many ways as
> underlying segments. You loose the only significant gain of the ways, the
> "fast-index" for group of  segments.


Agreed, in the worst case you would.  But most of the time you wouldn't.  It
would not be a good solution if in the worst case you had *more* ways than
segments, but that is not the case.


You will have all the difficulties mentioned earlier with map rendering,
> navigation, ..
>
> > When two ways share a segment there is a problem.  The
> direction has to  be the same for both ways.
>
> In my view, i would ignore the underlying direction except the oneway
> tag is set. You could omit the oneway tag and instead create a direction
> tag for each type of traffic.


Perhaps you could provide an example.  I don't understand how your proposed
solution would solve this problem.

I agree with Wollschafs definition of a way: a method to easily add tags
> to a lot of segments. For displaying, the API should combine the tags,
> given the most basic unit (the point) override the segments with overrides
> a way.
>
> A segment is a physical representation of the world, with tags like
> roadclass, type, bridge, tunnel, footway, speedlimit. So i would apply all
> tags of the physical world to a segment


A segment simply defines the _direction_ between two  nodes.  Apart from
tags it has two attributes; fromNode and toNode.  A Way with an _ordered_
list of nodes would do exactly the same thing.

A way is a logical group, like a bus-line, guided tour, think of somethink
> like that.
>
> To return to the question from the topic starter: Put the data in the
> segments. After that, group the segments to a way and tag the way with the
> name attribute.


DON'T put the data in the segments.  Tag the ways.

>
> > It is likely, IMHO, that segments will be removed rather than ways.  I'm
> > contemplating making the next major version of Osmarender ignore
> > segments completely (including all segment level attributes).
> >
>
> I must admit, i don't care, because i don't use Osmarenderer.


<nitpick>
  s/Osmarenderer/Osmarender/
</nitpick>



Christoph
>
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