On 03/10/2010 17:36, Peter Wendorff wrote:
On 03.10.2010 17:16, Ralf Kleineisel wrote:
On 10/03/2010 05:04 PM, Anthony wrote:
Maybe it's just because of where I live, but I don't see how it
would be.
Well, where I live (Germany) we have a legal limit of 100 kph on roads
outside of cities, motorways excluded. This legally applies even to
small roads if there is no sign indicating a lower limit. On many roads
you can achieve this speed, too. But on the other hand we have lots of
narrow, twisty country roads where a normal driver does not go faster
than 60 kph. In the Alps it is even more drastic. For estimating the
time someone will probably need to drive along a road this information
would be very helpful.
Sophisticated routing systems include the shape of roads (curves,
width, surface quality) and their importance for routing networks, but
I don't think, that should be added as mostly static attributes to the
osm database.
This would be a real huge effort, and I fear, it wouldn't really help.
To achieve a hopefully useful system, we would have to model:
- speed between monday and friday
- speed at weekends (in Germany different additional due to heavy
goods being forbidden to drive at weekends partly),
- speed at different daytimes,
- speed in different seasons (here where I live, there often is
agricultural traffic with really slow speed you have to wait behind;
at least in fall)
- speed at different weather conditions (rain, icy road, leaves at
autumn)
- speed at holiday times
To be useful, this has to be
- nearly complete
- up to date with changes at road network around
- measured in a slightly comparable, and objective fashion.
I think, that's neither possible nor useful inside the osm database.
I agree with your comment that it would be a huge effort, and I'm afraid
that storing objective data for all roads under all conditions would
also cause an explosion in the size of the database. Routing programs,
like many real-world programs, work with heuristics, deriving a value
that's *mostly good enough for practical purposes* from the available
data, possibly with a mechanism for an explicit override value for
pathological cases where the heuristics give completely wrong results.
These static values could then be adjusted according to dynamic data
such as weather or traffic conditions.
It would be good to have some input from an expert in navigation systems
to hear what kind of attributes would be useful for predicting journey
time for a. choosing the best route and b. informing the user of the
ETA. We can guess at road width, incline, curviness, priority at
junctions, number of lanes (?), legal maximum speed *for the road*...
Having got to some kind of data model for routing heuristic parameters
we can then talk about having deterministic defaults per territory - an
optimised algorithm for "what territory is point (X,Y) in" plus a
"table" of defaults for each territory. (Normally territory==country in
Europe but it doesn't need to be).
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