Model Implementation Example

In this example we will walk through creating a Model module. This Model will simply have pedestrians walking in circles around their initial position.

1. Create Folder and Files We will create the following:
   • modules/model/ExampleModel
   • modules/model/ExampleModel/ExampleModel.hpp
   • modules/model/ExampleModel/CMakeLists.txt
2. Create the model

   #include <vipra.hpp>
    
   // Create a new module, with it's C++ name and Module type (see Modules page for other types)
   VIPRA_NEW_MODULE(ExampleModel, Model) {
    public:
     // Give the module a name and set its type
     VIPRA_MODULE_NAME("ExampleModel")
     VIPRA_MODULE_TYPE(Model)
    
     // Add in the parameter registration step, this is where we tell VIPRA what parameters the module needs
     VIPRA_REGISTER_PARAMS ( 
       VIPRA_PARAM("radius", _radius);
     )
    
     // Add in the initialization step, this is run right before the simulation starts
     VIPRA_MODEL_INIT_STEP {
       _initialPoints = pedset.all_coords();
     }
    
     // Add in the timestep, this is where the model updates the pedestrians state
     VIPRA_MODEL_TIMESTEP {
       for (size_t i = 0; i < pedset.num_pedestrians(); ++i) {
         // Update the pedestrian's position, to make them move in a circle
         state.positions[i] = VIPRA::f3d{_initialPoints[i][0] + _radius * std::cos(deltaT * timestep),
                                         _initialPoints[i][1] + _radius * std::sin(deltaT * timestep)};
       }
     }
    
    private:
     // Member variables to hold the parameters
     VIPRA::f_pnt  _radius;
     VIPRA::f3dVec _initialPoints;
   };

3. Update main.cpp to use our new model

#include <vipra.hpp>
 
#include "modules/model/calm_model/calm_model.hpp"
 
auto main() -> int {
 
  // Create the simulation object, modules can be placed in any order so long as they are all there
  auto sim = VIPRA::simulation(
      Example::Model{},                       // Here, we use our new model
      VIPRA::Goals::AStar{},                  // Goals Module
      VIPRA::Pedestrians::Grid{},             // Pedestrian Set Module
      VIPRA::Map::QuadTree{}                  // Map Module
      VIPRA::Module::Output{                  // Output Coordinator
        VIPRA::Output::Trajectories::Json{}   // Output Module
      }
  );
 
  // Run the simulation, passing in parameters
  sim(
    VIPRA::Parameters{
      VIPRA::Input::Json{"maps/pedestrians/a320/a320_144_pedestrians.json"}, // Input Module for pedestrians
      VIPRA::Input::Json{"maps/obstacles/a320/a320_polygons.json"} // Input Module for obstalces
      VIPRA::Input::Json{"examples/module_params.json"} // Input Module for loading the parameters
    }
  );
}

1. Update the module_params.json

{
  "simulation": {
    "main": {
      "max_timestep": 10000,
      "timestep_size": 0.005,
      "output_frequency": 100,
      "random_seed": 12345
    }
  },
  "model": {     // Since our module is a model we put the parameters under the "model" field
    "example_model": {  // We add in a field with our module name
      "radius": 0.2     // Here is our radius parameter
    }
  },
  "goals": {
    "astar": {
      "endGoalType": "exit",
      "gridSize": 0.1,
      "closestObstacle": 0.25,
      "goalRange": 0.05
    }
  },
  "pedestrians": {
    "grid": {
      "gridSize": 0.5
    }
  },
  "obstacles": {
    "quad_tree": {
      "minQuadSize": 0.05
    }
  },
  "output": {
    "coordinator": {
      "output_dir": "./output"
    },
    "trajectories_json": {
      "filename": "trajectories.json"
    }
  },
  "behavior_model": {
    "main": {
      "behaviors_dir": "./behaviors",
      "behaviors": []
    }
  }
}

1. Adding CMakeLists.txt

vipra_add_all()

See the Base Module Implementation to see more.

1. Compile Simulation

The simulation can be compiled by running

make

1. Run

Run the simulation with

./VIPRA

The output will be under ./output/trajectories.json