On 2015-07-30 14:52, Greg Troxel wrote:
If there were to be a penalty (distinct from a time/distance estimate),
it should perhaps be for getting off a major road and getting back on.
But, one could argue that this would be kludgy, and if one wanted that,
the real issue would be that the underlying cost functions are wrong.
Perhaps in addition to the time spent at stop signs, lights, etc. there
should be a cost associated with the cognitive effort and accident
risk,
to be minimized, so that staying on the highway is treated as the
rational choice (that it probably actually is).
Penalties and costs are the basis of routing engines, not distance and
speed.
That is why OSMAND (and OSRM) make such silly mistakes as routing from
the motorway to an offramp and straight on to the onramp to join the
same motorway. Because both have the same speed limit and the offramp is
slightly shorter it would be faster?
Wrong. Faster is not the issue. The cost for using an offramp should be
higher than taking the motorway. Probably even the action of changing
from a certain class of way to the _link class (or indeed any lower
class) should incur a penalty.
A posted speed limit is just that: a legal maximum speed, not an actual
driven speed. And therefore of only limited use to a router. Sure, a
road with a posted speed limit of 30 will be slower than one with 120,
but it is wrong to assume that two roads with a speed limit of 120 will
be equally fast and therefor the shortest is always the better.
I too have the feeling that that notion does not live within the OSMAND
developers (nor the OSMR developers).
IMHO brouter.de does this very nicely. When I see that by tinkering with
the costs of certain road classes I can get a bicycle route exactly like
how I would drive it is an indication to me that it is a very life-like
router.
Regards,
Maarten
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