Am 05.04.2012 04:27, schrieb Eckhart Wörner:
Hi,
(sorry for starting a new thread, I just subscribed to the list)
infoware GmbH, Bonn, Germany, and Geofabrik GmbH, Karlsruhe, Germany, have
developed an improved tagging scheme for TMC data which we would like to
propopose to the OSM community.
I believe this is much needed, so thank you for starting this effort.
The one thing I like very much about the proposal is that it allows people to
start using TMC information without spending too much time implementing insane
heuristics or programming shortest path algorithms.
However, I feel like there are some problems with your design, which should be
discussed on a mailing list, since Wiki discussions are ugly.
1) The big problem: missing directional information
Let's assume there is a way in OSM tagged tmc=DE:123+456;DE:456-123. One also
has real-time traffic information that talks about a traffic jam at LCD 456,
negative direction, extent 1. One therefore knows that this traffic jam affects
DE:123-456, and since we have a way with that information, we know that this
way is affected.
However, there's one problem: which direction of the way is affected? It could
be either the direction from the first point of the way to the last (called
forward from now on), or vice versa (backward). This essential information is
missing and makes the TMC information on non-oneway ways useless.
There are several solutions to this problem. Probably the best solution is not
using the tmc tag at all, but using tmc:forward and tmc:backward instead. Thus
assuming the direction of the way is from LCD 123 to LCD 456, the tagging
would be tmc:forward=DE:123+456, tmc:backward=DE:456-123. "forward" and
"backward" are already used in tagging (for example, maxspeed:forward) and are
also protected by tools. E.g. if you try to reverse the before-mentioned way,
JOSM suggests to swap tmc:forward and tmc:backward (which is the correct thing
to do in that case).
That's no problem at all. The TMC direction must not be mixed up with
the driving direction, which here does not matter at all. All that
counts is the direction given (and defined) by the TMC data. If a
traffic event extends "forward" woth respect to the direction defined by
TMC, then "+" is used, if it extends in the revers direction, we use
"-". This is very concise, and using "forward" or "backward" instead
would just blow the tags.
2) A matter of taste: + and -
I'm not sure how others are feeling about this, but I find DE:123+456,
DE:456-123 somehow confusing. Here's an alternate proposal: DE:123+456 becomes
DE:123->456, and DE:456-123 becomes DE:123<-456 (notice the changed order).
Therefore, the LCD order is encoded in the position of the numbers, and the
movement between the LCDs is encoded in the arrow.
I would go even one step further and allow ← (LEFTWARDS ARROW; U+2190) and →
(RIGHTWARDS ARROW; U+2192) as an *alternative*. I know that not everybody
knows how to enter these codes, but every editor and every operating system
nowadays should be able to display them, and we have full unicode support in
the database.
Because of 1), DE:123/456 does not make sense at all.
OK, I think special unicode characters should not be used at all because
compatibility is uncertain and they are not available at any keyboard.
Using "+" and "-" is just straightforward. I would not expected
intereference or incompatibility with any other software from these, and
for the tests that we made so far everything works fine.
However, anybody having made experience with the issue what special
characters to use for tagging without running into compatiblilty
problems: Please would you share your ideas, your opinion is greatly
appreciated.
3) Bad influence: TMC information at junctions
One thing that I cannot wrap my head around is the TMC information *at*
junctions. As far as I remember, a traffic jam at LCD 456, negative direction,
extent 1 affects the road *between* LCD 123 and LCD 456, but not the actual
junctions 123 or 456. However, the rules of adding tmc tags to the actual
junctions influence a lot of maneuvers going over those junctions but not using
any other part of the way. This is especially true for roundabouts or
junctions between dual carriageways.
Please could you supply an image, or probably refer to the figures and
the numbering that we use in the proposals examples? That would make it
a lot clearer.
4) Exits and entries
TMC specifies messages that apply to entries or exits, which I feel are not
adequately represented in the proposal, even though the proposal mentions
them. For example, assume that the 2nd exit slip road going west at Köln-Süd
(where I already discovered the new tagging) is closed (and I believe there is
a TMC message for that). How do I find this 2nd slip road? (Yes, I picked a
really hard one.)
Isn't that just a matter of the granularity of TMC location coding
versus OSM mapping? If so, then there's nothing to help about that with
any TMC tagging scheme whatsoever.
5) Versioning
You argue that versioning is not needed, since data can be changed in a timely
manner, and the errors that appear are mostly harmless. I don't feel that way:
a) Experience tells that data is not always changed in a timely matter,
especially since TMC data does not appear on most of the maps. It takes a
while to process data (being half a month outdated seems to be normal even for
online routing), and offline maps make this situation worse (just look at the
bug reports at MapDust that appeared since Skobbler had started shipping offline
maps).
b) When LCDs are inserted into chains, things break *badly*, since the extents
are then out of sync as well.
Since TMC tags will simply be part of all other road network data that
any solution will use for mapping, navigaiton, etc., they will always
fit together from the time of creation. So there's n need for
versioning. On the other hand, it is abolutely certain that the issueing
organisations that are in charge of TMC (like BASt in Germany) will
never "re-cycle" previosly used location codes in a way that might
create trouble.
Eckhart Wörner
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Best regards,
Mit freundlichen Grüßen,
Heinrich Knauf
infoware GmbH
Riemenschneiderstr. 11
53175 Bonn
GERMANY
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office: +49 228 338899-21
email: kn...@infoware.de <mailto:kn...@infoware.de>
web: www.infoware.de <http://www.infoware.de>
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Geschäftsführer: Thomas Schulte-Hillen, Martin Langhoff;
Sitz Bonn; Amtsgericht Bonn HRB 14141
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