Calculating the distance between the current vehicle and the preceding vehicle

I have needed to calculate the distance between the current vehicle and the preceding vehicle,for each vehicle in a flow, running on an edge.

While going through TraCI, I came across getLeader method which is supposed to return the Id of the leader and the distance I need.

But I could not find a implemented method with this name, or any of the other method listed under Overview Extended Variables Retrieval written in C++ in TraCI.

I really appreciate if someone can help me with this.

I was successful in implementing getLastStepVehicleIDs to retrieve values from induction loops as advised here. I followed the already implemented methods of the same type (e.g. getJunctionIds), but in this case no such already implemented methods can be found.

Solution

There are plenty of functions to borrow from in TraCICommandInterface.cc. Without testing an implementation could look like this

std::pair<std:string, double> TraCICommandInterface::getLeader(const double lookahead) {
    TraCIBuffer request;
    request << static_cast<uint8_t>(VAR_LEADER) << nodeId
                    << static_cast<uint8_t>(TYPE_DOUBLE) << lookahead;
    TraCIBuffer response = connection.query(CMD_GET_VEHICLE_VARIABLE, request);

    uint8_t cmdLength; response >> cmdLength;
    if (cmdLength == 0) {
            uint32_t cmdLengthX;
            response >> cmdLengthX;
    }
    uint8_t responseId; response >> responseId;
    ASSERT(responseId == RESPONSE_GET_VEHICLE_VARIABLE);
    uint8_t variable; response >> variable;
    ASSERT(variable == VAR_LEADER);
    std::string id; response >> id;
    uint8_t typeId_r; response >> typeId_r; ASSERT(typeId_r == TYPE_COMPOUND);
    uint32_t compoundLength; response >> compoundLength; ASSERT(compoundLength == 2);
    uint8_t typeId_resp; response >> typeId_resp; ASSERT(typeId_resp == TYPE_STRING);
    std::string leader; response >> leader;
    uint8_t typeId_resp2; response >> typeId_resp2; ASSERT(typeId_resp2 == TYPE_DOUBLE);
    double dist; response >> dist;

    return std::make_pair(leader, dist);
}