Hi Phil,
Thanks for the extra info. I will download a fresh copy of maps for
Navit with the restrictions in place to make sure that junction works as
expected. I kind of figured out Navit's navigation must have thought
that route would have been shorter or better somehow - but in real life
it wouldn't have been a viable one.
I must admit I haven't figured out yet the business with trunk roads - I
always sort of assumed based on OSM's wiki that "A" roads in UK are
primary highways - clearly I must go back and read the OSM highway
classification again. It doesn't quite help the fact that tertiary
highways correspond to "C" roads, and secondary highways correspond to
"B" roads - thus living primary highways without a direct correspondent
in UK.
Regards,
Sebastian
On 16/12/12 19:37, Philip Barnes wrote:
The ahead only restrictions you have added should work, will have to
wait until Tuesday to see if they have worked in OSRM.
Apart from the missing restrictions, its one of those strange routing
algorithm things. It is taking that route because it reaches the trunk
road in a shorter distance.
OSM is based on the UK road classification system, so we have it easy. A
trunk road has green signs and usually but not always an A number (there
are B roads that are trunk), in other countries much discussion does go
into road classification and what is and isn't a trunk road.
Phil
On Sun, 2012-12-16 at 11:38 +0000, Sebastian Arcus wrote:
I have a question about how to correctly trace highway links at
junctions/intersections. Sometimes a link physically crosses over one or
two other lanes coming from the other direction of traffic, before
reaching the lane it is suppose to merge into. Now, these junction
points do exist in real life, but from the point of view of navigation
software, they are useless as one is not allowed to turn turn into any
of those lanes of traffic it crosses until it reaches the right lane it
is supposed to merge into.
My question is, should these junction/common points between paths
actually exist in OSM? Wouldn't it be better to draw the highway link
like it wouldn't actually intersect with those oncoming traffic lanes -
and just joined it to the final destination lane? I use Navit GPS - and
it sometimes assume I can turn into those oncoming traffic lanes just
because the common waypoint indicates there is a joint. Maybe other GPS
navigation software does the same mistake?
In case my explanation is a bit fuzzy, I will give an example. The
following relatively simple junction is in Liverpool:
http://www.openstreetmap.org/?lat=53.394271&lon=-2.982713&zoom=18
Imagine you are traveling northwards on Sefton Street towards the
junction. The right-most link (looking northwards, in the direction of
travel) is obviously a no-no as it is a one-way going south. However,
Navit suggested for some strange reason that I take the middle link, and
then turn immediately left on the first lane of traffic that the link
hits into Chaloner St and continue northward. In real life, that is
impossible, because that particular highway link (the middle one) is
only for crossing over the first two lanes of traffic it encounters, and
then merging with the far most one and continuing east on Parliament Street.
My thinking was that if the middle link coming from Sefton Street didn't
have common waypoints/joints with the first two lanes, the navigation
software would have never had any reason to suggest such a move. Those
points are as good as non-existent in practice, as they can't be used
for turning left or right into those two lanes.
Could anybody with more experience weigh in on this with some pro's or
con's please.
Thanks,
Sebastian
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