It is more than sufficient for a time calculation to use the maximum
speed, multiplied by some factor (smaller than 1), or even a fixed speed
per road class. My car navigation has this (there are three speeds I can
set) and usually the time is correct within a few minutes.
Much better is virtually impossible to achieve since you don't know how
much traffic there is on the road so you can not predict waiting times
at traffic lights or junctions.
But again: the duration of a route has nothing to do with the actual
route calculation. You first calculate the route based on cost factors
and then calculate the time you need based on speed profiles.
Maarten
On 2015-07-30 21:24, Colin Smale wrote:
I assume you are talking about typical speeds, and not a practical
maximum. A max speed will almost never be achieved, by definition
actually as the vehicle speeds will have a certain distribution. The
highest recorded speed will be the de facto practical maximum,
assuming the driver survived.
Routers could take account of hundreds of variables in their
calculation of predicted journey time from A to B, but in practice
their calculations make assumptions for most of them. For example,
most of them assume the vehicle is a car, that it is technically not
limited to any particular speed, that the weather is perfect, that it
is daytime, that the driver is not "inexperienced". And then there are
the other volatile variables like traffic density, road works,
oversize loads getting in the way etc.
Routers cannot take everything into account (this would preclude a lot
of preprocessing to simplify the real-time calculations), so they use
heuristics which work most often.
So how would you define the concept of "typical speed"?
--colin
On 30 July 2015 20:38:32 CEST, Richard <ricoz....@gmail.com> wrote:
On Thu, Jul 30, 2015 at 08:00:55PM +0200, Colin Smale wrote:
Practical maxspeed is useless as well. A straight wide road may be
capable of hosting land speed records, but traffic density is
likely to be a far more important factor.
yes, and this is what practical maxspeed is good for. Not
an ideal solution but works.
Richard
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