Behavior Tree XML Nodes

The nav2_behavior_tree package provides several navigation-specific nodes that are pre-registered and can be included in Behavior Trees.

Check this introduction to learn how behavior trees work and the difference between actions, conditions, controls and decorators.

Consider checking out the Groot Tutorials tutorial for using Groot to visualize and modify behavior trees.

Action Plugins

Wait Spin BackUp DriveOnHeading AssistedTeleop ComputePathToPose ComputeRoute ComputeAndTrackRoute FollowPath NavigateToPose ClearEntireCostmap ClearCostmapExceptRegion ClearCostmapAroundRobot ClearCostmapAroundPose ReinitializeGlobalLocalization TruncatePath TruncatePathLocal PlannerSelector ControllerSelector SmootherSelector GoalCheckerSelector ProgressCheckerSelector PathHandlerSelector NavigateThroughPoses ComputePathThroughPoses

RemovePassedGoals RemoveInCollisionGoals CancelControl CancelBackUp CancelSpin CancelWait CancelDriveOnHeading CancelAssistedTeleop CancelComputeAndTrackRoute SmoothPath GetPoseFromPath DockRobot UndockRobot ConcatenatePaths GetCurrentPose AppendGoalPoseToGoals ExtractRouteNodesAsGoals GetNextFewGoals ToggleCollisionMonitor FollowObject CancelFollowObject ValidatePath CheckPoseOccupancy CheckStopStatus

Condition Plugins

GoalReached TransformAvailable DistanceTraveled GoalUpdated GlobalUpdatedGoal InitialPoseReceived IsGoalNearby IsStuck TimeExpired IsBatteryLow IsWithinPathTrackingBounds PathExpiringTimer AreErrorCodesPresent WouldAControllerRecoveryHelp WouldAPlannerRecoveryHelp WouldASmootherRecoveryHelp WouldARouteRecoveryHelp IsBatteryCharging ArePosesNear

Control Plugins

PipelineSequence RoundRobin RecoveryNode NonblockingSequence PersistentSequence PauseResumeController

Decorator Plugins

RateController DistanceController SpeedController GoalUpdater PathLongerOnApproach SingleTrigger GoalUpdatedController

Example

This Behavior Tree replans the global path periodically at 1 Hz and it also has recovery actions.

<root main_tree_to_execute="MainTree">
  <BehaviorTree ID="MainTree">
    <RecoveryNode number_of_retries="6" name="NavigateRecovery">
      <PipelineSequence name="NavigateWithReplanning">
        <RateController hz="1.0">
          <RecoveryNode number_of_retries="1" name="ComputePathToPose">
            <ComputePathToPose goal="{goal}" path="{path}" planner_id="GridBased"/>
            <ReactiveFallback name="ComputePathToPoseRecoveryFallback">
              <GoalUpdated/>
              <ClearEntireCostmap name="ClearGlobalCostmap-Context" service_name="global_costmap/clear_entirely_global_costmap"/>
            </ReactiveFallback>
          </RecoveryNode>
        </RateController>
        <RecoveryNode number_of_retries="1" name="FollowPath">
          <FollowPath path="{path}" controller_id="FollowPath"/>
          <ReactiveFallback name="FollowPathRecoveryFallback">
            <GoalUpdated/>
            <ClearEntireCostmap name="ClearLocalCostmap-Context" service_name="local_costmap/clear_entirely_local_costmap"/>
          </ReactiveFallback>
        </RecoveryNode>
      </PipelineSequence>
      <ReactiveFallback name="RecoveryFallback">
        <GoalUpdated/>
        <RoundRobin name="RecoveryActions">
          <Sequence name="ClearingActions">
            <ClearEntireCostmap name="ClearLocalCostmap-Subtree" service_name="local_costmap/clear_entirely_local_costmap"/>
            <ClearEntireCostmap name="ClearGlobalCostmap-Subtree" service_name="global_costmap/clear_entirely_global_costmap"/>
          </Sequence>
          <Spin spin_dist="1.57"/>
          <Wait wait_duration="5"/>
          <BackUp backup_dist="0.15" backup_speed="0.025"/>
        </RoundRobin>
      </ReactiveFallback>
    </RecoveryNode>
  </BehaviorTree>
</root>