Re: [Routing] Roundabouts - why is a separate segment required?

[Marcus Wolschon]

Am 14.02.2018 um 18:21 schrieb Dave F:
> On 14/02/2018 16:46, Marcus Wolschon wrote:
>>
>> We often have roundabouts with dedicated lanes leading only to the
>> (heavily trafficed) exit
>> just off to the right. These are not part of the logical roundabout
>> and the particular traffic rules regarding
>> roundabouts do not apply. Yet they share nodes with the roundabout as
>> you can freely switch lanes in that circle segment.
>
> I think I understand what you're saying but for clarity could you
> provide an example.

The wiki page talks about them as "one way lateral shortcuts" just above
the seldom case of roads crossing the middle of the
roundabout. (I often see that as special ways for oversized transports
near industrial areas.)

The lane on the very right is such one.
https://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Blackwood_roundabout.jpg/1482px-Blackwood_roundabout.jpg

>
>> Only if you calculate the angle in an euclidian XY-plane for each one
>> and then sort them in clockwise
>> or counterclockwise fassion.
>
> The geometry is irrelevant. Entrances/exits can be determined because
> they don't contain a junction=roundabout tag.


It is not irrelevant as you need to tell the user "enter the roundabout
and use the THIRD exit".
How do you plan to determine how many exists to pass?


>
>> Assuming you can find out what side of the road people drive on in
>> this part of your route.
>
> Any person writing a routing/navigation shouldn't be doing it if they
> can't determine that. And anyway it's irrelevant to my point - it's
> the same in either direction.

It's not the same. Using the second exit from the right or the fourth
from the left is different.
Also this is one of the very few places where the direction of driving
actually matters for routing and only in your node-based aproach.
Simple because the tag oneway=yes is explicitely implied in the
segment-based aproach as stated on the Wiki page.

>
>> Something that can be avoided altogether with oneway segments making
>> up the roundabout.
>
> All ways with junction=roundabout are one way.

Yes and your proposal is a single node instead of a circle of segments.
How can a node be a oneway and thus determine a direction for counting
the exits?


>
>>
>>>
>>> DaveF.
>>>

 Phil (trigpoint)

 On 14 February 2018 15:38:01 GMT+00:00, Dave F
  wrote:

 To be doubly clear, this is an example of a road entering a roundabout 
 & 
 sharing a node with it:

 https://www.openstreetmap.org/node/19091900

>>
>> A nice example of 2 shared nodes making up 1 exit.
>>
>>
 Dave F.

 On 14/02/2018 15:21, Dave F wrote:

 On 14/02/2018 15:02, Marcus Wolschon wrote:

 What you describe is a mini-roundabout. 

 No it wasn't. It was perfectly clear as I posted the
 'junction=roundabout ' page. Much of the following is
 incoherent to me. The rest is irrelevant to my point.

>>
>> Irrelevant to your point but not to mine.
>>
>> The purpose of this map is much more then just routing for motorized
>> vehicles.
>> Representing the real road as accurate as possible is a major point here.
>> Or do you proclaim that e.g. accurate graphical rendering of a map is
>> not important for anyone?
>> That pedestian crossings on the legs of a roundabout are not
>> important for anyone?
>> That the roundabout-segment a postbox is at is not important for anyone?
>>
>> Also for vehicle routing, calculating the metrics as preicsely as
>> possible is a major
>> quality factor in good routing. So if using a roundabout is much
>> slower itself and
>> slows you down in front of (decellerating) and behind the roundabout
>> (accelerating)
>> compared to a simple right-turn, then this is an imporant thing to
>> model correctly.
>>
>> If a construction site or traffic jam blocks one exit, your model
>> would block the entire roundabout
>> instead of just that exist. Causing the driver to be routed way
>> around that intersection while for
>> his/her particular route it poses not much of an issue.
>>
>>
>>
 DaveF

 That has a different geometry as the center of that one
 is traversable.
 
 https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout
 a) I don't see a node as anything you "are on" at any
 time. Only segments. At most nodes are considered for
 calculating the metric of making certain turns between
 segments. b) Routing algorithms that don't know or deal
 with roundabouts would still work perfectly well with a
 circle of segments and give proper instructions. c) In
 reality this is a circle of road-segments. So segments
 represent reality more closely. So for the purpose of
 the 

Re: [Routing] Roundabouts - why is a separate segment required?

[Dave F]

On 14/02/2018 16:46, Marcus Wolschon wrote:


We often have roundabouts with dedicated lanes leading only to the 
(heavily trafficed) exit
just off to the right. These are not part of the logical roundabout 
and the particular traffic rules regarding
roundabouts do not apply. Yet they share nodes with the roundabout as 
you can freely switch lanes in that circle segment.


I think I understand what you're saying but for clarity could you 
provide an example.


Only if you calculate the angle in an euclidian XY-plane for each one 
and then sort them in clockwise

or counterclockwise fassion.


The geometry is irrelevant. Entrances/exits can be determined because 
they don't contain a junction=roundabout tag.


Assuming you can find out what side of the road people drive on in 
this part of your route.


Any person writing a routing/navigation shouldn't be doing it if they 
can't determine that. And anyway it's irrelevant to my point - it's the 
same in either direction.


Something that can be avoided altogether with oneway segments making 
up the roundabout.


All ways with junction=roundabout are one way.





DaveF.



Phil (trigpoint)

On 14 February 2018 15:38:01 GMT+00:00, Dave F 
 wrote:


To be doubly clear, this is an example of a road entering a roundabout &
sharing a node with it:

https://www.openstreetmap.org/node/19091900



A nice example of 2 shared nodes making up 1 exit.



Dave F.

On 14/02/2018 15:21, Dave F wrote:

On 14/02/2018 15:02, Marcus Wolschon wrote:

What you describe is a mini-roundabout. 


No it wasn't. It was perfectly clear as I posted the
'junction=roundabout ' page. Much of the following is
incoherent to me. The rest is irrelevant to my point.



Irrelevant to your point but not to mine.

The purpose of this map is much more then just routing for motorized 
vehicles.

Representing the real road as accurate as possible is a major point here.
Or do you proclaim that e.g. accurate graphical rendering of a map is 
not important for anyone?
That pedestian crossings on the legs of a roundabout are not important 
for anyone?

That the roundabout-segment a postbox is at is not important for anyone?

Also for vehicle routing, calculating the metrics as preicsely as 
possible is a major
quality factor in good routing. So if using a roundabout is much 
slower itself and
slows you down in front of (decellerating) and behind the roundabout 
(accelerating)
compared to a simple right-turn, then this is an imporant thing to 
model correctly.


If a construction site or traffic jam blocks one exit, your model 
would block the entire roundabout
instead of just that exist. Causing the driver to be routed way around 
that intersection while for

his/her particular route it poses not much of an issue.




DaveF

That has a different geometry as the center of that one
is traversable.
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout
a) I don't see a node as anything you "are on" at any
time. Only segments. At most nodes are considered for
calculating the metric of making certain turns between
segments. b) Routing algorithms that don't know or deal
with roundabouts would still work perfectly well with a
circle of segments and give proper instructions. c) In
reality this is a circle of road-segments. So segments
represent reality more closely. So for the purpose of
the map as a representation of real world geometry, this
is simply a much better approximation. This is not only
for routing but also for map-rendering to scale the size
of the roundabout correctly. (There are vast differences
in possible sizes.) d) These segments have a
significantly different metric then an intersection
(much slower traffic in the roundabout then the
surrounding roads). They have an angle to the entering
and exiting road that can be used in a metric because
you need to slow down to make such hard turns, limiting
your average speed in the segments before and after the
roundabout (lookahead). There may be traffic jams or
construction sites blocking part of a roundabout but
still allowing certain turns to be made. This can not be
described with a simple node. On 2018-02-14 15:40, Dave
F wrote:

Hi Could anyone give me an explanation for this line
from
https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout
"Each road has to be connected with the roundabout
in a separate node—that is, between these nodes a
segment of the roundabout is required." I see no
requirement for 

Re: [Routing] Roundabouts - why is a separate segment required?

[Marcus Wolschon]

Am 14.02.2018 um 16:55 schrieb Dave F:
>
>
> On 14/02/2018 15:46, Philip Barnes wrote:
>> If an entering way shares a node with an exiting way there is no need
>> to pass through a roundabout way
>
> If that shared node is also part of junction=roundabout, then it does
> "need to pass through".


We often have roundabouts with dedicated lanes leading only to the
(heavily trafficed) exit
just off to the right. These are not part of the logical roundabout and
the particular traffic rules regarding
roundabouts do not apply. Yet they share nodes with the roundabout as
you can freely switch lanes in that circle segment.


>
>
>
>> It also messes up the exit count in navigation instructions.
>
> How? It has the same number of exits/entrances, no matter if they
> share nodes. They're all still countable.

Only if you calculate the angle in an euclidian XY-plane for each one
and then sort them in clockwise
or counterclockwise fassion.
Assuming you can find out what side of the road people drive on in this
part of your route.
Something that can be avoided altogether with oneway segments making up
the roundabout.

>
> DaveF.
>
>>
>> Phil (trigpoint)
>>
>> On 14 February 2018 15:38:01 GMT+00:00, Dave F
>>  wrote:
>>
>> To be doubly clear, this is an example of a road entering a roundabout & 
>> sharing a node with it:
>>
>> https://www.openstreetmap.org/node/19091900
>>

A nice example of 2 shared nodes making up 1 exit.


>>
>> Dave F.
>>
>> On 14/02/2018 15:21, Dave F wrote:
>>
>> On 14/02/2018 15:02, Marcus Wolschon wrote:
>>
>> What you describe is a mini-roundabout. 
>>
>> No it wasn't. It was perfectly clear as I posted the
>> 'junction=roundabout ' page. Much of the following is
>> incoherent to me. The rest is irrelevant to my point.
>>

Irrelevant to your point but not to mine.

The purpose of this map is much more then just routing for motorized
vehicles.
Representing the real road as accurate as possible is a major point here.
Or do you proclaim that e.g. accurate graphical rendering of a map is
not important for anyone?
That pedestian crossings on the legs of a roundabout are not important
for anyone?
That the roundabout-segment a postbox is at is not important for anyone?

Also for vehicle routing, calculating the metrics as preicsely as
possible is a major
quality factor in good routing. So if using a roundabout is much slower
itself and
slows you down in front of (decellerating) and behind the roundabout
(accelerating)
compared to a simple right-turn, then this is an imporant thing to model
correctly.

If a construction site or traffic jam blocks one exit, your model would
block the entire roundabout
instead of just that exist. Causing the driver to be routed way around
that intersection while for
his/her particular route it poses not much of an issue.



>> DaveF
>>
>> That has a different geometry as the center of that one
>> is traversable.
>> https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout
>> a) I don't see a node as anything you "are on" at any
>> time. Only segments. At most nodes are considered for
>> calculating the metric of making certain turns between
>> segments. b) Routing algorithms that don't know or deal
>> with roundabouts would still work perfectly well with a
>> circle of segments and give proper instructions. c) In
>> reality this is a circle of road-segments. So segments
>> represent reality more closely. So for the purpose of the
>> map as a representation of real world geometry, this is
>> simply a much better approximation. This is not only for
>> routing but also for map-rendering to scale the size of
>> the roundabout correctly. (There are vast differences in
>> possible sizes.) d) These segments have a significantly
>> different metric then an intersection (much slower
>> traffic in the roundabout then the surrounding roads).
>> They have an angle to the entering and exiting road that
>> can be used in a metric because you need to slow down to
>> make such hard turns, limiting your average speed in the
>> segments before and after the roundabout (lookahead).
>> There may be traffic jams or construction sites blocking
>> part of a roundabout but still allowing certain turns to
>> be made. This can not be described with a simple node. On
>> 2018-02-14 15:40, Dave F wrote:
>>
>> Hi Could anyone give me an explanation for this line
>> from
>> https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout
>> "Each road has to be connected with the roundabout in
>> a separate 

Re: [Routing] Roundabouts - why is a separate segment required?

[Dave F]

On 14/02/2018 15:46, Philip Barnes wrote:
If an entering way shares a node with an exiting way there is no need 
to pass through a roundabout way


If that shared node is also part of junction=roundabout, then it does 
"need to pass through".





It also messes up the exit count in navigation instructions.


How? It has the same number of exits/entrances, no matter if they share 
nodes. They're all still countable.


DaveF.



Phil (trigpoint)

On 14 February 2018 15:38:01 GMT+00:00, Dave F 
 wrote:


To be doubly clear, this is an example of a road entering a roundabout &
sharing a node with it:

https://www.openstreetmap.org/node/19091900

Dave F.

On 14/02/2018 15:21, Dave F wrote:

On 14/02/2018 15:02, Marcus Wolschon wrote:

What you describe is a mini-roundabout. 


No it wasn't. It was perfectly clear as I posted the
'junction=roundabout ' page. Much of the following is
incoherent to me. The rest is irrelevant to my point. DaveF

That has a different geometry as the center of that one is
traversable.
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout
a) I don't see a node as anything you "are on" at any
time. Only segments. At most nodes are considered for
calculating the metric of making certain turns between
segments. b) Routing algorithms that don't know or deal
with roundabouts would still work perfectly well with a
circle of segments and give proper instructions. c) In
reality this is a circle of road-segments. So segments
represent reality more closely. So for the purpose of the
map as a representation of real world geometry, this is
simply a much better approximation. This is not only for
routing but also for map-rendering to scale the size of
the roundabout correctly. (There are vast differences in
possible sizes.) d) These segments have a significantly
different metric then an intersection (much slower traffic
in the roundabout then the surrounding roads). They have
an angle to the entering and exiting road that can be used
in a metric because you need to slow down to make such
hard turns, limiting your average speed in the segments
before and after the roundabout (lookahead). There may be
traffic jams or construction sites blocking part of a
roundabout but still allowing certain turns to be made.
This can not be described with a simple node. On
2018-02-14 15:40, Dave F wrote:

Hi Could anyone give me an explanation for this line
from
https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout
"Each road has to be connected with the roundabout in
a separate node—that is, between these nodes a segment
of the roundabout is required." I see no requirement
for a separate segment:  * When a entering road
shares a node with a roundabout then the router knows
it's entered that roundabout by reading the tags on
the circular way.  * Whilst on that node, the
router checks to see if there are any suitable exits.
If there are, then it leaves the roundabout.  * If
not, it continues going around until it finds an
appropriate exit.  Cheers DaveF


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Re: [Routing] Roundabouts - why is a separate segment required?

[Philip Barnes]

If an entering way shares a node with an exiting way there is no need to pass 
through a roundabout way to navigate between them hence the roundabout will not 
be seen. It also messes up the exit count in navigation instructions. 

Phil (trigpoint) 

On 14 February 2018 15:38:01 GMT+00:00, Dave F  
wrote:
>To be doubly clear, this is an example of a road entering a roundabout
>& 
>sharing a node with it:
>
>https://www.openstreetmap.org/node/19091900
>
>Dave F.
>
>On 14/02/2018 15:21, Dave F wrote:
>> On 14/02/2018 15:02, Marcus Wolschon wrote:
>>> What you describe is a mini-roundabout.
>>
>> No it wasn't.
>> It was perfectly clear as I posted the 'junction=roundabout ' page.
>>
>> Much of the following is incoherent to me. The rest is irrelevant to 
>> my point.
>>
>> DaveF
>>
>>> That has a different geometry as the center of that one is
>traversable.
>>> https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout
>>>
>>> a)
>>> I don't see a node as anything you "are on" at any time. Only
>segments.
>>> At most nodes are considered for calculating the metric of making 
>>> certain turns
>>> between segments.
>>> b)
>>> Routing algorithms that don't know or deal with roundabouts would 
>>> still work
>>> perfectly well with a circle of segments and give proper
>instructions.
>>> c)
>>> In reality this is a circle of road-segments. So segments represent 
>>> reality more closely.
>>> So for the purpose of the map as a representation of real world 
>>> geometry, this is simply
>>> a much better approximation. This is not only for routing but also 
>>> for map-rendering
>>> to scale the size of the roundabout correctly. (There are vast 
>>> differences in possible sizes.)
>>> d)
>>> These segments have a significantly different metric then an 
>>> intersection (much slower traffic
>>> in the roundabout then the surrounding roads).
>>> They have an angle to the entering and exiting road that can be used
>
>>> in a metric because you
>>> need to slow down to make such hard turns, limiting your average 
>>> speed in the segments before and
>>> after the roundabout (lookahead).
>>> There may be traffic jams or construction sites blocking part of a 
>>> roundabout but still
>>> allowing certain turns to be made. This can not be described with a 
>>> simple node.
>>>
>>>
>>> On 2018-02-14 15:40, Dave F wrote:
 Hi
 Could anyone give me an explanation for this line from
 https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout

 "Each road has to be connected with the roundabout in a separate
 node—that is, between these nodes a segment of the roundabout is
 required."

 I see no requirement for a separate segment:

  * When a entering road shares a node with a roundabout then
>the
 router knows it's entered that roundabout by reading the tags on
>the
 circular way.
  * Whilst on that node, the router checks to see if there are
>any
 suitable exits. If there are, then it leaves the roundabout.
  * If not, it continues going around until it finds an
>appropriate
 exit.

  Cheers
 DaveF
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>>
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Re: [Routing] Roundabouts - why is a separate segment required?

[Dave F]

To be doubly clear, this is an example of a road entering a roundabout & 
sharing a node with it:


https://www.openstreetmap.org/node/19091900

Dave F.

On 14/02/2018 15:21, Dave F wrote:

On 14/02/2018 15:02, Marcus Wolschon wrote:

What you describe is a mini-roundabout.


No it wasn't.
It was perfectly clear as I posted the 'junction=roundabout ' page.

Much of the following is incoherent to me. The rest is irrelevant to 
my point.


DaveF


That has a different geometry as the center of that one is traversable.
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout

a)
I don't see a node as anything you "are on" at any time. Only segments.
At most nodes are considered for calculating the metric of making 
certain turns

between segments.
b)
Routing algorithms that don't know or deal with roundabouts would 
still work

perfectly well with a circle of segments and give proper instructions.
c)
In reality this is a circle of road-segments. So segments represent 
reality more closely.
So for the purpose of the map as a representation of real world 
geometry, this is simply
a much better approximation. This is not only for routing but also 
for map-rendering
to scale the size of the roundabout correctly. (There are vast 
differences in possible sizes.)

d)
These segments have a significantly different metric then an 
intersection (much slower traffic

in the roundabout then the surrounding roads).
They have an angle to the entering and exiting road that can be used 
in a metric because you
need to slow down to make such hard turns, limiting your average 
speed in the segments before and

after the roundabout (lookahead).
There may be traffic jams or construction sites blocking part of a 
roundabout but still
allowing certain turns to be made. This can not be described with a 
simple node.



On 2018-02-14 15:40, Dave F wrote:

Hi
Could anyone give me an explanation for this line from
https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout

"Each road has to be connected with the roundabout in a separate
node—that is, between these nodes a segment of the roundabout is
required."

I see no requirement for a separate segment:

 * When a entering road shares a node with a roundabout then the
router knows it's entered that roundabout by reading the tags on the
circular way.
 * Whilst on that node, the router checks to see if there are any
suitable exits. If there are, then it leaves the roundabout.
 * If not, it continues going around until it finds an appropriate
exit.

 Cheers
DaveF
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Re: [Routing] Roundabouts - why is a separate segment required?

[Dave F]

On 14/02/2018 15:02, Marcus Wolschon wrote:

What you describe is a mini-roundabout.


No it wasn't.
It was perfectly clear as I posted the 'junction=roundabout ' page.

Much of the following is incoherent to me. The rest is irrelevant to my 
point.


DaveF


That has a different geometry as the center of that one is traversable.
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout

a)
I don't see a node as anything you "are on" at any time. Only segments.
At most nodes are considered for calculating the metric of making 
certain turns

between segments.
b)
Routing algorithms that don't know or deal with roundabouts would 
still work

perfectly well with a circle of segments and give proper instructions.
c)
In reality this is a circle of road-segments. So segments represent 
reality more closely.
So for the purpose of the map as a representation of real world 
geometry, this is simply
a much better approximation. This is not only for routing but also for 
map-rendering
to scale the size of the roundabout correctly. (There are vast 
differences in possible sizes.)

d)
These segments have a significantly different metric then an 
intersection (much slower traffic

in the roundabout then the surrounding roads).
They have an angle to the entering and exiting road that can be used 
in a metric because you
need to slow down to make such hard turns, limiting your average speed 
in the segments before and

after the roundabout (lookahead).
There may be traffic jams or construction sites blocking part of a 
roundabout but still
allowing certain turns to be made. This can not be described with a 
simple node.



On 2018-02-14 15:40, Dave F wrote:

Hi
Could anyone give me an explanation for this line from
https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout

"Each road has to be connected with the roundabout in a separate
node—that is, between these nodes a segment of the roundabout is
required."

I see no requirement for a separate segment:

 * When a entering road shares a node with a roundabout then the
router knows it's entered that roundabout by reading the tags on the
circular way.
 * Whilst on that node, the router checks to see if there are any
suitable exits. If there are, then it leaves the roundabout.
 * If not, it continues going around until it finds an appropriate
exit.

 Cheers
DaveF
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Re: [Routing] Roundabouts - why is a separate segment required?

[Marcus Wolschon]

What you describe is a mini-roundabout.
That has a different geometry as the center of that one is traversable.
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmini_roundabout

a)
I don't see a node as anything you "are on" at any time. Only segments.
At most nodes are considered for calculating the metric of making 
certain turns

between segments.
b)
Routing algorithms that don't know or deal with roundabouts would still 
work

perfectly well with a circle of segments and give proper instructions.
c)
In reality this is a circle of road-segments. So segments represent 
reality more closely.
So for the purpose of the map as a representation of real world 
geometry, this is simply
a much better approximation. This is not only for routing but also for 
map-rendering
to scale the size of the roundabout correctly. (There are vast 
differences in possible sizes.)

d)
These segments have a significantly different metric then an 
intersection (much slower traffic

in the roundabout then the surrounding roads).
They have an angle to the entering and exiting road that can be used in 
a metric because you
need to slow down to make such hard turns, limiting your average speed 
in the segments before and

after the roundabout (lookahead).
There may be traffic jams or construction sites blocking part of a 
roundabout but still
allowing certain turns to be made. This can not be described with a 
simple node.



On 2018-02-14 15:40, Dave F wrote:

Hi
Could anyone give me an explanation for this line from
https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout

"Each road has to be connected with the roundabout in a separate
node—that is, between these nodes a segment of the roundabout is
required."

I see no requirement for a separate segment:

* When a entering road shares a node with a roundabout then the
router knows it's entered that roundabout by reading the tags on the
circular way.
* Whilst on that node, the router checks to see if there are any
suitable exits. If there are, then it leaves the roundabout.
* If not, it continues going around until it finds an appropriate
exit.

 Cheers
DaveF
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