[Talk-us] Am I mapping this wrong, or should the router be fixed for this?

Paul Johnson baloo at ursamundi.org
Fri Jul 31 10:37:03 UTC 2015


On Thu, Jul 30, 2015 at 7:52 AM, Greg Troxel <gdt at ir.bbn.com> wrote:
>
> I've been on the osmand list for over a year, and the issue of routing
> choices similar to yours have come up multiple times.  It seems that the
> views of the osmand developers (who are not very active on the list) are
> different from the consensus on the list.
>
> The issue of on-ramps/off-ramps tagged as *_link has been a particular
> discussion focus.  The notion you expressed that these don't have actual
> posted limits, just sometimes yellow signs is indeed shared by most in
> the discussions.  And we generally agree that the right speed to use for
> them is more or less half the speed of the larger road from which the
> links go to/from.  Perhaps half the speed of the actual road, perhaps
> half the speed of a nominal road of that class, and perhaps slower.
> But these are fine details, and the consensus is pretty strong.
>

Half the speed of associated major way in _link situations would at least
be a rational default averaging out from what I've seen here in Oklahoma
(though might be too generous for urban areas, anything that's posted 'LAST
 EXIT BEFORE TOLL' at rush hour as everyone cheaps out simultaneously).
http://wiki.openstreetmap.org/wiki/Key:maxspeed:advisory is also a tag we
should be using and that osmand should be looking for (but in practice,
neither happens).


> I do not understand why the osmand devleopers don't just implement this
> notion; it seems relatively obviously correct, and people who have
> modified their routing.xml files report reasonable results.
>
> A few further thoughts:
>
> While it's important to tag actual speed limits (posted, or
> unambiguously determined from local law, such as 30 mph in thickly
> settled areas in Massachusetts), routers should actually function on
> typical speeds, not limits.  I think osm should have this data, but it
> gets a bit complicated.


planet.gpx, but should go by typical speeds, advised speed, or the legal
maxspeed, whichever of those three are lowest (no reason a safe and
professional driver in a tall vehicle should get told that they can get
there faster than is realistically probable; always better to say it's
going to take longer than it will in reality).


> Still, a simple take on it would help a lot.
> One could just put in the yellow-sign value as typical.  Or perhaps
> there should be a warning-sign tag, and a typical determined from a
> number of tracks.  (Around me, there's a highway with limit 65 mph, and
> I'd say typical is 75 mph.  Ramps are often yellow-signed at 30 mph and
> typical is 40mph on some of them.)
>

Sounds very similar to the situation here, even on new sections recently
modernized.


>   3) choosing a function to minimize.   Shortest distance and shortest
>   time are both not right, as dangerous maneuvers are avoided by many
>   people even if they save a few seconds.


Unless you're basically every cabbie ever.  ;o)


> And then there's avoiding highly bumpy roads.
>

"Avoid US", but that may complicate routing for this audience.


> In 2, there should be a time penalty for u-turns.  Really it's not a
>
penalty: it's an estimate of how much time it actually takes, and
> ideally these times would be extracted from actual tracks so the actual
> time and the predicted time match in some zero-mean sense.
>

The faster the road, the higher the penalty should be for that, too.
Doesn't have to be a U-turn, either, just any hard turn (particularly
across traffic (usually left in this country but just about every city's
got some funky one-offs where the opposite is true).
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