Re: [sumo-user] getSubscriptionResults in libtraci / C++

[Ruud van Gaal <r.vangaal@xxxxxxxxxx>]

Hi Bart,

I haven't really used arrival/departure a lot, since I have mostly flow vehicles. But at the beginning I used code like this, notably *outside* of the subscription results:

    int n=Simulation::getArrivedNumber();
    if(n>0) {
      pt_Log("Query vehicles: arrivedNumber=%d",n);

      auto id_list=Simulation::getArrivedIDList();
      for(auto id:id_list) {
        pt_Log("- %s",id.c_str());
      }
    }

Probably departure works exactly the same, but using getDepartedNumber() and getDepartedIDList().

This has to be called after every simulation step. To avoid missing vehicles that arrive or depart, do call Simulation::step(0) instead of taking multiple steps (Simulation::step(new_time)). The getArrivedNumber() call only reports vehicles from the last simulation step. Also, when overruling properties of vehicles, you need to make sure you do this on every simulation step, and not take large jumps.

As for keeping track of vehicle ID's, I keep a list of all vehicle ID's that I see in the subscription results. Then I remove and add vehicles as they disappear from the subscription results. This is slightly different from trying to keep a list of ALL vehicles in SUMO (which can be thousands); I only track the closest 50 or so within a radius.

I guess for your case, keeping a local vehicle ID list and adding ID's as they are seen with 'getDepartedIDList()' and remove them when you see the ID in getArrivedIDList() is a nice way to keep an overview of all active vehicles within SUMO. There is a call to get them all, but the fewer calls to sumo-gui (over relatively slow TCP), the better.

Cheers,

Ruud

On Tue, Dec 5, 2023 at 5:35 PM T Eenachtacht <t188012021@xxxxxxxxx> wrote:

HI Ruud,

Yes i do subscribe during initialisation (before the first simulation step) for both VAR_DEPARTED_VEHICLES_IDS and VAR_ARRIVED_VEHICLES_IDS.

Vehicle_ids seem to be generated by SUMO only during the simulation when a vehicle departs. So as soon as the above subscription gives a new vehicle id the vehicle subscription can be done. 

Both subscriptions work fine. I can also receive and process subscription results for a specific vehicle, when i subscribe with a hard coded vehicle id.

The only thing i do not understand how to get the vehicle_id from the libtraci::Simulation subscription results. I expect some type of list or vector of vehicle ids in the subscription results, but 'r.second()->getString().c_str()' does not yield any vehicleid, or anything readable anyway. 

Can you explain or give an example how to get every single vehicle id from the subscription results to VAR_DEPARTED_VEHICLES_IDS?

Thanks a lot,

Bart

On 05-12-2023 17:09, Ruud van Gaal wrote:

Hi Bart,

Yes, all subscribe results are returned in one batch. But that is probably the better thing to do. Realise that all these calls are really TCP send & receive calls to 'sumo-gui' or 'sumo'. So if you would intend to call getSubscriptionResults() multiple times per simulation step (each with a different filter), you're probably reducing performance quite a bit.

So it's better to cache the results and make multiple passes in your own code instead of calling expensive TraCI functions.

So something like this would be much faster:

void ProcessSubResults()

{

  auto sub_results = Vehicle::getSubscriptionResults(name.c_str());

  ProcessArrivedVehicles(sub_results);

  ProcessDepartedVehicles(sub_results);

}

void ProcessArrivedVehicles(...) {...}

You probably have something like this at subscription init time already; do you request VAR_ARRIVED_VEHICLES_IDS when subscribing?

  std::vector<int> vars;
  // Info we need from vehicles in vicinity
  vars.push_back(libsumo::VAR_SPEED);
  vars.push_back(libsumo::VAR_ANGLE);
  vars.push_back(libsumo::VAR_SLOPE);
  vars.push_back(libsumo::VAR_SIGNALS);
  vars.push_back(libsumo::VAR_POSITION3D);
  Vehicle::subscribeContext(veh_id, libsumo::CMD_GET_VEHICLE_VARIABLE, prefSubscribeDistance, vars);

So, get all sub results in one call (which is probably one TCP send and receive call in the background), then do processing on the batch of results in your own code (where it's now local in memory).

Indeed, the variable id (int) is the first item of every pair.

Cheers,

Ruud

On Tue, Dec 5, 2023 at 3:41 PM T Eenachtacht <t188012021@xxxxxxxxx> wrote:

Hi Ruud,

Thank you very much for the snippets. Very useful for my next step to extract vehicle information.

As the first step i would like to get a list of the vehicle ids that just departed from the simulation (or newly arrived) to manage my internal list of active vehicles. From your first example it seems the results cannot be filtered to only the VAR_ARRIVED_VEHICLES_IDS or VAR_DEPARTED_VEHICLES_IDS Instead all subscribed results are returned in the sub_results map. The first element of the map is the variable ID, correct? Then i would expect the second element is a list of vehicle ids:

    auto sub_results = Vehicle::getSubscriptionResults(name.c_str());
    for (auto r : sub_results) {
        int var_id = r.first();     

        if (var_id == libsumo::VAR_ARRIVED_VEHICLES_IDS) {

            char const* vehicle_ids = r.second()->getString().c_str();

        }

    }

However, the vehicle_ids string does seems to contain any vehicle ids, list or ...

Is it possible to get just the list of vehicle ids in the C++ lib (like in Python), and if so how, or do i need to determine that from the individual vehicles results like in your second example?

Thanks,

Bart

On 05-12-2023 10:12, Ruud van Gaal wrote:

Hi Bart,

Here are some snippets. For getSubscriptionResults():

    auto sub_results = Vehicle::getSubscriptionResults(name.c_str());
    for (auto r : sub_results) {
      pt_LogDbg("- Ego subscr result type 0x%x: '%s'", r.first, r.second->getString().c_str());
    }

I'm using a context subscription really (only report within a specific radius):

  libsumo::SubscriptionResults subscriptionResults;
  if (prefLogSumoCalls)
    pt_Log("SUMO call: Vehicle::getContextSubscriptionResults(%s)", name.c_str());

  subscriptionResults = Vehicle::getContextSubscriptionResults(name.c_str());

  // Go through results (parse)
  std::string entity_id;
  for (auto e : subscriptionResults) {
    entity_id = e.first;
    //pt_LogDbg("- Ego ctx subscr result type '%s'", entity_id.c_str());

    auto res = e.second;
    for (auto r : res) {
      //pt_LogDbg("  - subscr result var 0x%x value '%s''", r.first, r.second->getString().c_str());
      switch (r.first) {
        case libsumo::VAR_ANGLE:
          vehicle->angle = ParseDouble(r.second->getString());
          break;
        case libsumo::VAR_POSITION3D:

           // Convert string to Vector3-like struct
          ParsePosition(r.second->getString(), vehicle->position);
          break;
        case libsumo::VAR_TYPE:
          //pt_LogDbg("VAR_TYPE='%s'", r.second->getString().c_str());
          vehicle->type_sumo = r.second->getString();

          break;

        //////////////// etc
        default:
          pt_LogWarn("Var 0x%x is not parsed; fix the source", r.first);
          break;
      }
    }
  }

Hope that helps,

Ruud

On Mon, Dec 4, 2023 at 11:35 PM T Eenachtacht via sumo-user <sumo-user@xxxxxxxxxxx> wrote:

Dear All,

Does anyone have experience, or can send a link to documentation, on how to process results from a subscription in C++ using libtraci? I need to convert the following from Python into C++. The subscription is for multiple types of variables. (not only VAR_ARRIVED_VEHICLES_IDS).

In Python the implementation is rather straightforward with the documentation (e.g. in https://sumo.dlr.de/docs/TraCI/Interfacing_TraCI_from_Python.html).

results = traci.simulation.getSubscriptionResults()

for vehicle_id in results[tc.VAR_ARRIVED_VEHICLES_IDS]:

# process vehicle_id

This can be converted to C++ like this:

libsumo::TraCIResults results = libtraci::Simulation::getSubscriptionResults();

//std::map<int, std::shared_ptr<libsumo::TraCIResult> > libsumo::TraCIResults

for (auto entry : results) {

int i = entry.first;

shared_ptr<libsumo::TraCIResult> result = entry.second;

How can the TraCIResults be filtered for ' libsumo::VAR_ARRIVED_VEHICLES_ID' values, and

how to get the id values from the result?

Thanks for the help,

Bart Netten

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