Tasks

Description

Tasks define the high-level objectives that an agent must complete in a given Environment, subject to certain constraints (e.g. not flip over).

Tasks have two important internal variables:

• _termination_conditions: a dict of {str: TerminationCondition} that define when an episode should be terminated. For each of the termination conditions, termination_condition.step(...) returns a tuple of (done [bool], success [bool]). If any of the termination conditions returns done = True, the episode is terminated. If any returns success = True, the episode is cnosidered successful.
• _reward_functions: a dict of {str: RewardFunction} that define how the agent is rewarded. Each reward function has a reward_function.step(...) method that returns a tuple of (reward [float], info [dict]). The reward is a scalar value that is added to the agent's total reward for the current step. The info is a dictionary that can contain additional information about the reward.

Tasks usually specify task-relevant observations (e.g. goal location for a navigation task) via the _get_obs method, which returns a tuple of (low_dim_obs [dict], obs [dict]), where the first element is a dict of low-dimensional observations that will be automatically flattened into a 1D array, and the second element is everything else that shouldn't be flattened. Different types of tasks should overwrite the _get_obs method to return the appropriate observations.

Tasks also define the reset behavior (in-between episodes) of the environment via the _reset_scene, _reset_agent, and _reset_variables methods.

• _reset_scene: reset the scene for the next episode, default is scene.reset().
• _reset_agent: reset the agent for the next episode, default is do nothing.
• _reset_variables: reset any internal variables as needed, default is do nothing.

Different types of tasks should overwrite these methods for the appropriate reset behavior, e.g. a navigation task might want to randomize the initial pose of the agent and the goal location.

Usage

Specifying

Every Environment instance includes a task, defined by its config that is passed to the environment constructor via the task key. This is expected to be a dictionary of relevant keyword arguments, specifying the desired task configuration to be created (e.g. reward type and weights, hyperparameters for reset behavior, etc). The type key is required and specifies the desired task class. Additional keys can be specified and will be passed directly to the specific task class constructor. An example of a task configuration is shown below in .yaml form:

point_nav_example.yaml

task:
  type: PointNavigationTask
  robot_idn: 0
  floor: 0
  initial_pos: null
  initial_quat: null
  goal_pos: null
  goal_tolerance: 0.36    # turtlebot bodywidth
  goal_in_polar: false
  path_range: [1.0, 10.0]
  visualize_goal: true
  visualize_path: false
  n_vis_waypoints: 25
  reward_type: geodesic
  termination_config:
    max_collisions: 500
    max_steps: 500
    fall_height: 0.03
  reward_config:
    r_potential: 1.0
    r_collision: 0.1
    r_pointgoal: 10.0

Runtime

Environment instance has a task attribute that is an instance of the specified task class. Internally, Environment's reset method will call the task's reset method, step method will call the task's step method, and the get_obs method will call the task's get_obs method.

Types

OmniGibson currently supports 5 types of tasks, 7 types of termination conditions, and 5 types of reward functions.

Task

DummyTask Dummy task with trivial implementations. termination_conditions: empty dict. reward_functions: empty dict. _get_obs(): empty dict. _reset_scene(): default. _reset_agent(): default.

PointNavigationTask PointGoal navigation task with fixed / randomized initial pose and goal location. termination_conditions: MaxCollision, Timeout, PointGoal. reward_functions: PotentialReward, CollisionReward, PointGoalReward. _get_obs(): returns relative xy position to the goal, and the agent's current linear and angular velocities. _reset_scene(): default. _reset_agent(): sample initial pose and goal location.

PointReachingTask Similar to PointNavigationTask, except the goal is specified with respect to the robot's end effector. termination_conditions: MaxCollision, Timeout, PointGoal. reward_functions: PotentialReward, CollisionReward, PointGoalReward. _get_obs(): returns the goal position and the end effector's position in the robot's frame, and the agent's current linear and angular velocities. _reset_scene(): default. _reset_agent(): sample initial pose and goal location.

GraspTask Grasp task for a single object. termination_conditions: Timeout. reward_functions: GraspReward. _get_obs(): returns the object's pose in the robot's frame _reset_scene(): reset pose for objects in _objects_config. _reset_agent(): randomize the robot's pose and joint configurations.

BehaviorTask BEHAVIOR task of long-horizon household activity. termination_conditions: Timeout, PredicateGoal. reward_functions: PotentialReward. _get_obs(): returns the existence, pose, and in-gripper information of all task relevant objects _reset_scene(): default. _reset_agent(): default.

Follow our tutorial on BEHAVIOR tasks!

To better understand how to use / sample / load / customize BEHAVIOR tasks, please read our BEHAVIOR tasks documentation!

TerminationCondition

Timeout FailureCondition: episode terminates if max_step steps have passed.

Falling FailureCondition: episode terminates if the robot can no longer function (i.e.: falls below the floor height by at least fall_height or tilt too much by at least tilt_tolerance).

MaxCollision FailureCondition: episode terminates if the robot has collided more than max_collisions times.

PointGoal SuccessCondition: episode terminates if point goal is reached within distance_tol by the robot's base.

ReachingGoal SuccessCondition: episode terminates if reaching goal is reached within distance_tol by the robot's end effector.

GraspGoal SuccessCondition: episode terminates if target object has been grasped (by assistive grasping).

PredicateGoal SuccessCondition: episode terminates if all the goal predicates of BehaviorTask are satisfied.

RewardFunction

CollisionReward Penalization of robot collision with non-floor objects, with a negative weight r_collision.

PointGoalReward Reward for reaching the goal with the robot's base, with a positive weight r_pointgoal.

ReachingGoalReward Reward for reaching the goal with the robot's end-effector, with a positive weight r_reach.

PotentialReward Reward for decreasing some arbitrary potential function value, with a positive weight r_potential. It assumes the task already has get_potential implemented. Generally low potential is preferred (e.g. a common potential for goal-directed task is the distance to goal).

GraspReward Reward for grasping an object. It not only evaluates the success of object grasping but also considers various penalties and efficiencies. The reward is calculated based on several factors: Grasping reward: A positive reward is given if the robot is currently grasping the specified object. Distance reward: A reward based on the inverse exponential distance between the end-effector and the object. Regularization penalty: Penalizes large magnitude actions to encourage smoother and more energy-efficient movements. Position and orientation penalties: Discourages excessive movement of the end-effector. Collision penalty: Penalizes collisions with the environment or other objects.