Car-Following Model

This short document describes how a new car-following model can be added to SUMO. We'll do this by implementing a test model named "smartSK". When implementing your own model, you should also grep (look for) occurrences of the name we use, here.

## The car-following model's class

The best thing is to start with an already existing model. Models are located in <SUMO_HOME>/src/microsim/cfmodels and new added models should reside here, too. Copy both MSCFModel_KraussOrig1.h and MSCFModel_KraussOrig1.cpp and rename them. The name should be "MSCFModel_<YOUR_MODELS_NAME>", in our case "MSCFModel_SmartSK"

Convention

Car-following model implementations are located in <SUMO_HOME>/src/microsim/cfmodels.

Convention

A car-following class' name should start with "MSCFModel_".

Now, open both files and rename all occurrences of MSCFModel_KraussOrig1 into your class' name.

Add the files to the <SUMO_HOME>/src/microsim/cfmodels/CMakeLists.txt.

## Loading into simulation

We now add the XML-elements which allow us to define and parse the model's parameter. Extend the list of known elements "SUMOXMLDefinitions::tags" located in <SUMO_HOME>/src/utils/xml/SUMOXMLDefinitions.cpp. In SUMOXMLDefinitions.h:

    SUMO_TAG_CF_SMART_SK,

In SUMOXMLDefinitions.cpp:

    { "carFollowing-SmartSK",     SUMO_TAG_CF_SMART_SK },

Furthermore you need to add an entry to SUMOXMLDefinitions::carFollowModelValues[] also in SUMOXMLDefinitions.cpp:

    { "SmartSK",     SUMO_TAG_CF_SMART_SK },

Car-following models are instantiated in MSVehicleType::build(...) located in <SUMO_HOME>/src/microsim/MSVehicleType.cpp. You'll find a switch, here where you have to put the call to your model's constructor into.

    case SUMO_TAG_CF_SMART_SK:
      model = new MSCFModel_SmartSK(vtype,
                                    from.getCFParam(SUMO_ATTR_ACCEL, SUMOVTypeParameter::getDefaultAccel(from.vehicleClass)),
                                    from.getCFParam(SUMO_ATTR_DECEL, SUMOVTypeParameter::getDefaultDecel(from.vehicleClass)),
                                    from.getCFParam(SUMO_ATTR_SIGMA, SUMOVTypeParameter::getDefaultImperfection(from.vehicleClass)),
                                    from.getCFParam(SUMO_ATTR_TAU, 1.),
                                    from.getCFParam(SUMO_ATTR_TMP1, 1.),
                                    from.getCFParam(SUMO_ATTR_TMP1, 1.),
                                    from.getCFParam(SUMO_ATTR_TMP1, 1.),
                                    from.getCFParam(SUMO_ATTR_TMP1, 1.),
                                    from.getCFParam(SUMO_ATTR_TMP1, 1.));

You may note that the constructor is read with values from "from". The first parameter, starting with SUMO_ATTR_ denotes the XML-attribute which names the parameter. These attributes, if new, have to be added to <SUMO_HOME>. In SUMOXMLDefinitions.h:

    SUMO_ATTR_TMP1,
    SUMO_ATTR_TMP2,
    SUMO_ATTR_TMP3,
    SUMO_ATTR_TMP4,
    SUMO_ATTR_TMP5,

In SUMOXMLDefinitions.cpp:

    { "tmp1",           SUMO_ATTR_TMP1 },
    { "tmp2",           SUMO_ATTR_TMP2 },
    { "tmp3",           SUMO_ATTR_TMP3 },
    { "tmp4",           SUMO_ATTR_TMP4 },
    { "tmp5",           SUMO_ATTR_TMP5 },

The second parameter denotes the default value. There are two different mechanisms to define default values. Either they are vehicle class independent (they are the same for passenger cars and for trucks for instance) then you can simply state the number here or you want a different default for the different vehicle classes then insert the relevant code into <SUMO_HOME>/src/utils/vehicle/SUMOVTypeParameter.cpp. You can only have floating point values as model parameters at the moment.

You also have to define which parameter must be read in <SUMO_HOME>/src/utils/vehicle/SUMOVehicleParserHelper.cpp, method getAllowedCFModelAttrs():

    std::set<SumoXMLAttr> smartSKParams;
    smartSKParams.insert(SUMO_ATTR_ACCEL);
    smartSKParams.insert(SUMO_ATTR_DECEL);
    smartSKParams.insert(SUMO_ATTR_SIGMA);
    smartSKParams.insert(SUMO_ATTR_TAU);
    smartSKParams.insert(SUMO_ATTR_TMP1);
    smartSKParams.insert(SUMO_ATTR_TMP2);
    smartSKParams.insert(SUMO_ATTR_TMP3);
    smartSKParams.insert(SUMO_ATTR_TMP4);
    smartSKParams.insert(SUMO_ATTR_TMP5);
    allowedCFModelAttrs[SUMO_TAG_CF_SMART_SK] = smartSKParams;

Note, that we have to adapt the constructor to retrieve the additional parameter (tmp1-tmp5). We have also to adapt the copy constructor located in our class in MSCFModel_SmartSK::duplicate(...).

For further interaction, you also have to adapt the "id" of the model in the model's .h class:

    virtual int getModelID() const {
     return SUMO_TAG_CF_SMART_SK;
    }

## Using Custom Parameters via TraCI

A carFollowModel can override the functions getParameter and setParameter inherited from MSCFModel. Any calls to 'traci.vehicle.setParameter' and 'traci.vehicle.getParameter' where the key starts with "carFollowModel." will then be forwarded to these methods (without the prefix). The call `traci.vehicle.setParameter(vehID, "carFollowModel.XYZ", "42")` will be mapped onto the call `MSCFModel::setParameter(MSVehicle* veh, "XYZ" , "42")` which is called on the current carFollowModel of the vehicle.

## XML Validation

Sumo performs xml validation. If you add new XML elements or attributes you either need to adapt the XML schema files in <SUMO_HOME>/data/xsd or add the option

    --xml-validation never

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