Initialisation:
First of all we have to initialize the required structs, which are stored and described in the header file "road.h".



The structs are required for the function "RoadRouteGetDrvStops". For this the DrvStopIn-struct contains the input parameters and the DrvStopOut-struct the results of the function. The content of the structs is described in the IPGRoad API documentation or in the "road.h" header file. Please have a look on it.

The function "RoadRouteGetDrvStops" will then pass in the DrvStopOut-struct the objectID of the stop marker and the associated traffic light controller for the required route. The output value of the function corresponds to the number of detected traffic lights and can be at most the value 3, since with the help of this function at most the next three traffic lights can be detected. Therefore, an array of 3 DrvStopOut constructs is also formed during initialization. If all traffic lights of a route of the ego vehicle would be interesting, you would have to use the function "RoadRouteGetAllDrvStops".

Code implementation:
The next figure describes the code we have to add to the User_Calc function of the User.c file:



First we check with the if-condition whether the TestRun was started, because User_Calc will be executed even if no simulation was started. We only have to execute these functions while driving/simulating. With the AND operation and the second condition using the module division, the function will be executed every x main cycles (here: with the value 1 the functions of the IPGRoad API inside User_Calc are executed every main cycle).

Input Parameters:
Next we have to define the input parameters of the DrvStopIn construct. The passed DrvStopIn.objId describes the object ID of the route. You can take this e.g. from the Scenario Editor or automatically from the "Environment.h" header file via the global Struct and its fields "Env.Route.ObjId".



The DrvStopIn.mask describes which specific stop markers you are interested in and filters out accordingly. For this purpose a binary value must be passed, e.g. for Traffic Light stop markers the binary number sequence: 0 0 1 0 0. RDST_TrfLight is an enum and substitutes the value 2. With the left shift operator you consequently create the binary number sequence mentioned above. You can also select other stop markers. You can find out which stop markers are available for filtering using the IPGRoad API documentation under the search term "enum tRoadDrvStopType".

The range of the area to be examined DrvStopIn.range is shifted along the route with the offset DrvStopIn.s. In our case shown, we defined the s coordinate of the vehicle along the route for the offset. For the range, we defined an arbitrary value of 100. This gives us the instantaneous distance relative to the ego vehicle to the next three detected traffic lights that are within 100 m of the vehicle while the simulation is running. You could also specify a fixed value here, but this would always give you the same distance to the first three detected traffic lights.

Executing the evaluation functions:
Finally, we apply the function "RoadRouteGetDrvStops" and get the number of detected stop markers of the corresponding traffic lights, which is stored in the variable "int numTrfLight" and additionally the objectID of the respective stop marker and traffic light controller in the output structure DrvStopOut. An example of the output can be seen in the following figure:



Next we pass the Traffic Light Controller ID of the first detected traffic light ("DrvStopOut[0].ctrlObjId") to the function "TrfLight_Object_LookupByObjId". The latter function comes from the "TrfLight.h" header file. The return value "int TrfLightNo" now contains the position of the corresponding traffic light in the array "TrfLight.Objs".

Extracting the state of the traffic light:
Finally we pass this integer to the mentioned array with "TrfLight.Objs[TrfLightNo].State" and get as a return value the state of the traffic light (green, yellow, red). Further information, like the position of the graphic object of the traffic light in the global coordinate system Fr0, can be taken from the TrfLight-struct:



These members of the struct are also described in the "TrfLight.h" header file.