User:Erik Lundin/Routing and enforcement
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Due to the proposal of enforcement, I started to think of how to place the nodes to best interact with software that might be using the feature. Does it matter to a routing software if the distance between the "from" node and the camera is 5 or 500 meters? To straighten my thoughts out I've constructed some cases (mostly with enforcement example 3b in mind) which highlights some aspects that I think has to be considered when interacting with for instance routing software.
What I'm searching for is an algorithm that handles the cases in a satisfying way, and what implications that has for how to place the nodes in the enforcement relation.
Case 1:
__ (50) >#
-= ó~~ò | |
-------------------------------------------------*-----------|-------|-----*----------
/ from / to
This driver wants a warning device
before the changed speed limit.
Case 2:
__ >#
-= ó~~ò |
---*---------------------------------------------------------------------------------|-----*----------
from / / to
And this one doesn't want device
to hear anything until here
(say 150 m. from camera).
Case 3:
>#
|
-----------------*--------------------------------+------------------------|-------*-------
from | / to
| device
|
| <- Intersecting
/o| road
The driver here doesn't --> | ||
really need to know about |_o|
the camera until he turns |
right. He has to slow |||
down in the intersection. ||
|
|
|
Case 4:
>#
|
-----------------*-----------------------------------------------+---------|-------*-------
from ´ / to
´ device
__ ´
-= ó~~ò ´
------------------------------- ´
/
This driver would like to
know about the camera quite
soon, because he doesn't
need to slow down where the
two roads are merging.
Approaches/algorithms
I claim in no way that I know how to write routing software, but these are the main approaches I intuitively can think of when it comes to how to detect a speed camera and warn the driver:
A - Plain distance
Found a camera
If (The distance (or time) to the camera < threshold &&
Speed > maximum allowed)
Then warn the driver
- + Simple.
- + Will work for case 1, 2 and 4.
- + Independent of where "from" is placed.
- - Warns for cameras aiming in the opposite direction.
- - Will warn the driver in case 3 even if he intends to turn left.
- - Will continue to warn when you have passed the camera, until the distance is big enough.
B - Vectors (dot product)
Found a camera
Calculate the dot product of the vector from-to (normalised) and the velocity vector of the vehicle.
It will be at a maximum when we're approaching the camera front to front in high speed.
If (The dot product > some threshold &&
Distance (or time) to the camera < some other threshold &&
Speed > maximum allowed)
Then warn the driver
- + Elegant solution.
- + Will work for case 1, 2, and 3.
- + Stops warning when you have passed the camera.
- - The "from" and "to" nodes have to be placed so the line between them lines up with the road.
- - Possible bad performance for cars approaching the camera in a curve - need to be examined.
C - Close enough AND is between "from" and "to"
Found a camera
If (The distance (or time) to the camera < threshold &&
We're on a road section between "from" and "to" &&
Speed > maximum allowed)
Then warn the driver
- + Will work for case 2.
- + The driver in case 3 doesn't have to bother about the camera if he not turns right in the intersection.
- - Needs "from" to be placed far enough from the camera.
- - Doesn't provide a solution to case 1 and 4.
- - Will continue to warn when you have passed the camera, until the distance is big enough or you have passed "to".
D - Close enough OR is between "from" and "to"
Found a camera
If ((The distance (or time) to the camera < threshold ||
We're on a road section between "from" and "to") &&
Speed > maximum allowed)
Then warn the driver
- + Will work for case 1.
- - Needs "from" to be placed close enough to the camera.
- - Warns for cameras aiming in the opposite direction.
- - Doesn't provide a solution to case 2.
- - Will warn the driver in case 3 even if he intends to turn left.
- - Will continue to warn when you have passed the camera, until the distance is big enough and you have passed "to".
E - Mini routing
Found a camera
Calculate the route between current position and the camera
If (The distance (or time) to the camera < threshold &&
Calculated route has some section common with from-to &&
Speed > maximum allowed
Then warn the driver
- + Will work for case 1, 2 and 4.
- + Independent of where "from" is placed.
- + Stops warning when you have passed the camera.
- - Possible somewhat more cpu-intensive due to the routing.
- - Will warn the driver in case 3 even if he intends to turn left.