[OSM-talk-be] Fietsknooppunten, bicycle nodes "Roundabouts and around squares"

[marc at vmarc.be]

Jakka,

> I cut the roundabouts in pieces highway to highway. Is this the 
> properly way?
> But gives the tester prg like http://osma.vmarc.be/ ... an alert?

The logic in osma.vmarc.be is intended to work OK independent of whether 
the roundabout is mapped as a single way in a closed loop and tag 
"junction=roundabout", or cut into different ways, each with or without 
tag "junction=roundabout".

For hiking networks the analyzer is intended to choose the shortest 
path. For bicycle networks the analyzer is intended to follow the 
direction of the ways in as mapped in the round-about.

> Roundabouts you must take at the right hand.(Europe)

The analyzer assumes the actual direction of the ways adhere to this 
rule and currently has no logic to verify if this is really the case. 
According to the wiki 
(http://wiki.openstreetmap.org/wiki/Tag:junction=roundabout) this should 
be a fair assumption: quote: "The OSM ways of the roundabout itself must 
be drawn in the direction the traffic flows."

For an example of a roundabout that is not split into different ways you 
can look at the roundabout close to the start node in route 
http://osma.vmarc.be/en/route/1029070. If you zoom in on the roundabout 
in the map and hoover over the different parts of the roundabout, you 
will see that one part of the roundabout is chosen for the forward path 
of the route (from low node number to high node number), and the other 
part for the backward path (from high node number to low node number).  
The other two roundabouts in this route are cut into different ways. 
Here also the different parts are assigned to the proper forward and 
backward path.

Ways that are closed loops are handled similar to roundabouts. Route 
http://osma.vmarc.be/en/route/1173862 has such a closed loop without tag 
"junction=roundabout" (way 6849252) at the end node of the route. Only 
the parts of the way that are actually used in the forward and the 
backward paths of the route are used (note that the bit at the north 
side is not used in forward nor the backward path).


With respect to route 2718669: the analysis result in 
http://osma.vmarc.be/en/route/2718669 currently thinks this route is not 
OK because it does not find an end node for the route in any of the ways 
in the route relation. The start node 1442170312 (which is part of way 
202508685) does have a tag rcn_ref=5, but there is no node with such tag 
in any of the other ways of the route, also not in the last way 
163973463. When I add rcn_ref=99 in node 1489841045, then the analyzer 
logic thinks this route is completely OK (apart for an informational 
message RouteNodeNameMismatch because the analyzer does not expect the 
text "Verlaine-sur-Ourthe" in the route name).  I do not see any ways 
with tag "junction=roundabout" in this route though.

> a large square, marketplace, which cannot be tagged as roundabout ...

An example in a walking-network of a marketplace that is mapped with a 
single way in a closed loop can be found in the last way of route 
http://osma.vmarc.be/en/route/3145182. This way is recognized by the 
analysis logic as a loop and treated the same as a roundabout. Because 
this is a walking network, the analyzer chooses the shortest path to the 
destination node. In route http://osma.vmarc.be/en/route/3941922 another 
part of the of the same way is chosen as shortest path.


To summarize, it should be OK to map roundabouts either as a single way 
or cut into separate ways. Either way of mapping a roundabout will have 
its pros and cons. The logic in osma.vmarc.be is intended to understand 
roundabouts and loops, and do the right thing, independent of how they 
are mapped. The intention is to not have "alerts" or "false positives" 
for this.

I am sure the analysis logic in osma.vmarc.be is not OK yet in all 
possible situations. If you have examples where you have doubts or see 
analysis results that are just plain wrong, I would like to hear about 
this. I think there are still a lot things to be improved.

Regards,
Marc
(osma.vmarc.be developer)