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.

Note: SingleTrigger BT Node is not listed below because it contains no parameters.

Consider checking out the Groot - Interacting with Behavior Trees tutorial for using Groot to visualize and modify behavior trees.

Action Plugins

• Wait
• Spin
• BackUp
• ComputePathToPose
• FollowPath
• NavigateToPose
• ClearEntireCostmap
• ClearCostmapExceptRegion
• ClearCostmapAroundRobot
• ReinitializeGlobalLocalization
• TruncatePath
• PlannerSelector
• ControllerSelector
• GoalCheckerSelector
• NavigateThroughPoses
• ComputePathThroughPoses
• RemovePassedGoals

Condition Plugins

• GoalReached
• TransformAvailable
• DistanceTraveled
• GoalUpdated
• InitialPoseReceived
• IsStuck
• TimeExpired
• IsBatteryLow

Control Plugins

• PipelineSequence
• RoundRobin
• RecoveryNode

Decorator Plugins

• RateController
• DistanceController
• SpeedController
• GoalUpdater

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>