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User:PesachZ/algorithm

1,420 bytes added, 6 years ago
added that the client doesn't give a CONTINUE instruction, spell check
== General comments ==
The description below fits a right turn in a [[Right-hand traffic|Right-hand traffic]] country (e.g.  not England). Left turns are symmetrical to right turns.
== Definitions ==
To better be able to put the algorithm into words, we have to name each of the road segments that connect to a junction. These are ''subjective names'', they are relative to which segment the junction is being approached from, and which segment the routing server wants to navigate to after passing through the junction.
Start with the juntion junction in the middle. 
#'''s-in:&nbsp;'''The segment the vehicle is on as it approaches the juntion junction will be called&nbsp;'''s-in'''.#'''s-out:&nbsp;'''The segment the vehicle is being routed onto after it passes through the junction will be called '''s-out'''. This can be any of the other segments connected to the junction, which will also be one of the segments named below as <span data-scaytid="85" data-scayt_word="s1">s1</span>, <span data-scaytid="87" data-scayt_word="s2">s2</span>, ... etc..#'''<span data-scaytid="86" data-scayt_word="s1">s1</span>, <span data-scaytid="88" data-scayt_word="s2">s2</span>, <span data-scaytid="89" data-scayt_word="s3">s3</span>, <span data-scaytid="90" data-scayt_word="s4">s4</span>, etc.:&nbsp;'''All the segments connected to the same junction, (including s-out) will be each be named consecutively as '''<span data-scaytid="91" data-scayt_word="s1">s1</span>, <span data-scaytid="92" data-scayt_word="s2">s2</span>, etc., '''''for as many segments as there are'''''… <span data-scaytid="93" data-scayt_word="sN">sN</span>'''. One of these numbered segments will also be s-out.#'''Best Continuation:&nbsp;'''One of the segments leaving the junction will be considered the 'Best Continuation'. This is the segment that <span data-scaytid="94" data-scayt_word="Waze ">Waze</span> determines is what drivers would consider the "no turning path" or "going straight" through the intersection. The criteria <span data-scaytid="95" data-scayt_word="Waze">Waze </span> uses to determine which segment is the 'Best Continuation' is explained below.
http://i.imgur.com/59WbakW.jpg
== Best Continuation ==
In order to determine if s-out is the 'real' continuation of s-in, we do <span data-scaytid="96" data-scayt_word="Waze">Waze</span> does the following:
#If s-out has the same road type & street name it is selected as the real continuation.
#If not, we look at the other segments: <span data-scaytid="97" data-scayt_word="s1">s1</span>, <span data-scaytid="98" data-scayt_word="s2">s2 </span> <span data-scaytid="99" data-scayt_word="sN ">sN</span> (excluding s-out). One of those will be chosen as a better continuation than s-out if both following conditions are met:#*This segment has a better match street name & road type wise than s-out (e.g. &nbsp;it has the same street name and s-out doesn't; it has the same road type as s-in, and s-out doesn't). Street name is more important than road type.
#*The angle between this segment and s-in is smaller than the angle between s-out and s-in
#If both condtions conditions are not met, then s-out is considered to be the 'best continuation'.
=== Special Considerations ===
*In some situations a [[Junction Style Guide#Y Intersections|Y-Intersection]] (where there are more than one segment leaving the junction node at less than a 45° angle), navigation to either segment will generate a 'KEEP RIGHT/LEFT" instruction, even if one of those would otherwise be the 'best continuation' and has a departure angle of 0° from s-in. This is also mentioned in the [[Junction Style Guide#Wayfinder Segments|<span data-scaytid="100" data-scayt_word="wayfinder">wayfinder </span> section]].*A segment (<span data-scaytid="101" data-scayt_word="s1">s1</span>, <span data-scaytid="102" data-scayt_word="s2">s2</span>, ...sN) leaving the juction junction which has the trun turn into it from s-in [[Turn restrictions#Turn restrictions .28allowed turns.29|restricted]] in [[Waze Map Editor|<span data-scaytid="103" data-scayt_word="WME">WME</span>]]&nbsp;will not be considered in this algorithm as a 'best continuation', even if it has&nbsp;a departure angle of 0° from s-in.http://i.imgur.com/TUEyvEZ.jpg
== The algorithm / list of conditions ==
2. If the angle between s-out and the best continuation is larger than 45 degrees (and less than 180), the instruction is: 'TURN RIGHT'. This is because we assume that on primary roads (minor highways, major highways and freeways), turn angles are no more than 45 degrees (no sharp turns on higher-throughput roads); therefore, you never have something called an "exit" that has such an angle, and the instruction should be TURN, not EXIT.
3. If s-out is determined to be the best continuation of s-in (explanation on 'best continuation' above), the instruction is: 'CONTINUE', which implies that the driver is not turning (i.e., going straight through the junction). <u>''By design the client does not give this instruction.''</u>
4. If s-in is a primary road and s-out is not a primary road (<span data-scaytid="104" data-scayt_word="mH">mH</span>, MH, FW), the instruction is: 'EXIT RIGHT'.
5. If s-in is a ramp/exit and s-out is neither a primary road&nbsp;(<span data-scaytid="105" data-scayt_word="mH">mH</span>, MH, FW), nor a ramp/exit, the instruction is: 'EXIT RIGHT'.
6. If none of the above conditions is met, the instruction is: 'KEEP RIGHT'
== T junctions and one way roads ==
In some cases, a node could have more than 2 segments, but the routing server will consider only 2 of them as valid and therefore, the maneuver will be 'Continue straight'.<br/>Turns can be [[Turn restrictions#Turn restrictions .28allowed turns.29|restricted or unrestricted]], in specific scenarios you may not be able to see this in [[Waze Map Editor|<span data-scaytid="106" data-scayt_word="WME">WME</span>]] - see&nbsp;[[Reverse connectivity#Reverse Connectivity|<span data-scaytid="107" data-scayt_word="RevCons">RevCons</span>]]&nbsp;for more information.
For example, in this case (image below) - assuming the node is restricted properly - heading south, the right turn will be considered 'Continue straight' as the routing server has no other option and there's only one possible segment to be s-out.
If the node was not restricted, most likely that waze <span data-scaytid="108" data-scayt_word="Waze">Waze</span> would tell you to turn right. Driving against the direction is a high&nbsp;[[Routing penalties|penalty]], and so is a left turn where a turn is not allowed. However, it would still have been an option, which is why the routing server would have called it 'turn right'.
https://wiki.waze.com/wiki/images/0/00/Right_turn_1.png
This could be confusing, especially since there's no external indication on whether or not a node is restricted at the moment. There are external scripts which show this information (and some allow it to be easily corrected) - see&nbsp;[[Reverse connectivity#Reverse Connectivity|<span data-scaytid="109" data-scayt_word="RevCons">RevCons</span>]]&nbsp;for more information.