# World¶

The world in BARK contains all objects of the simulation. It is modeled as a simultaneous-move game where all agents act at the same time. Each agent moves according to its defined behavior, execution, and dynamic model. After all agents have been moved, the overall validity is then checked.

The World class is defined as

class World {
public:
void Step(float delta_time);
...
private:
MapInterface map_interface_;
AgentMap agents_;
ObjectMap objects_;
double world_time_;
}.


The MapInterface contains the map, functionalities for routing, and simplified structures for the agents to plan in. The AgentMap contains all agents of the simulation and the ObjectMap all static objects. Finally, the World class also contains the simulation world time world_time_.

## Observed World¶

In each simulation step, an agent in BARK gets passed an ObservedWorld that is derived from the current World. The agent then plans in this derived world and returns a trajectory. The ObservedWorld provides additional interfaces and allows to model further features, such as e.g. occlusions. Besides providing additional functionalities, it also defines and saves the ego agent id ego_agent_id_.

class ObservedWorld : public World {
public:
ObservedWorld(const WorldPtr& world, const AgentId& ego_agent_id) :
World(world),
ego_agent_id_(ego_agent_id) {}
...
private:
AgentId ego_agent_id_;
};


## Objects and Agents¶

In BARK objects are static and can be extended to dynamic agents. Objects in BARK have a position, a shape, and an ObjectId. The agent extends this by adding a behavior, execution, and dynamic model as described here. Additionally, the agent also has a GoalDefinitionPtr and RoadCorridorPtr.

The agent class is defined as follows:

class Agent : public Object {
public:
friend class World;

Agent(const State& initial_state,
const BehaviorModelPtr& behavior_model_ptr,
const DynamicModelPtr& dynamic_model_ptr,
const ExecutionModelPtr& execution_model,
const geometry::Polygon& shape,
const commons::ParamsPtr& params,
const GoalDefinitionPtr& goal_definition = GoalDefinitionPtr(),
const MapInterfacePtr& map_interface = MapInterfacePtr(),
const geometry::Model3D& model_3d = geometry::Model3D());
...
private:
BehaviorModelPtr behavior_model_;
DynamicModelPtr dynamic_model_;
ExecutionModelPtr execution_model_;