Behavior-Tree Navigator¶

Source code on Github.

The BT Navigator (Behavior Tree Navigator) module implements the NavigateToPose task interface. It is a Behavior Tree-based implementation of navigation that is intended to allow for flexibility in the navigation task and provide a way to easily specify complex robot behaviors, including recovery.

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

Parameters¶

navigators

Type	Default
vector<string>	{‘navigate_to_pose’, ‘navigate_through_poses’}

Description: New to Iron: Plugins for navigator types implementing the nav2_core::BehaviorTreeNavigator interface. They implement custom action servers with custom interface definitions and use that data to populate and process behavior tree navigation requests. Plugin classes are defined under the same namespace, see examples below. Defaults correspond to the NavigateToPoseNavigator and NavigateThroughPosesNavigator navigators.

default_nav_to_pose_bt_xml

Type	Default
string	N/A

Description: Path to the default behavior tree XML description for NavigateToPose, see Behavior Tree XML Nodes for details on this file. Used to be default_bt_xml_filename pre-Galactic.

default_nav_through_poses_bt_xml

Type	Default
string	N/A

Description: Path to the default behavior tree XML description for NavigateThroughPoses, see Behavior Tree XML Nodes for details on this file. New to Galactic after NavigateThroughPoses was added.

plugin_lib_names

Type

Default

vector<string>

[“nav2_compute_path_to_pose_action_bt_node”, “nav2_follow_path_action_bt_node”, “nav2_back_up_action_bt_node”, “nav2_spin_action_bt_node”, “nav2_wait_action_bt_node”, “nav2_clear_costmap_service_bt_node”, “nav2_is_stuck_condition_bt_node”, “nav2_goal_reached_condition_bt_node”, “nav2_initial_pose_received_condition_bt_node”, “nav2_goal_updated_condition_bt_node”, “nav2_reinitialize_global_localization_service_bt_node”, “nav2_rate_controller_bt_node”, “nav2_distance_controller_bt_node”, “nav2_speed_controller_bt_node”, “nav2_recovery_node_bt_node”, “nav2_pipeline_sequence_bt_node”, “nav2_round_robin_node_bt_node”, “nav2_transform_available_condition_bt_node”, “nav2_time_expired_condition_bt_node”, “nav2_distance_traveled_condition_bt_node”, “nav2_single_trigger_bt_node”]

Description: List of behavior tree node shared libraries.

bt_loop_duration

Type	Default
int	10

Description: Duration (in milliseconds) for each iteration of BT execution.

default_server_timeout

Type	Default
int	20

Description: Default timeout value (in milliseconds) while a BT action node is waiting for acknowledgement from an action server. This value will be overwritten for a BT node if the input port “server_timeout” is provided.

transform_tolerance

Type	Default	Unit
double	0.1	seconds

Description: TF transform tolerance.

global_frame

Type	Default
string	map

Description: Reference frame.

robot_base_frame

Type	Default
string	base_link

Description: Path to behavior tree XML description.

odom_topic

Type	Default
string	odom

Description: Topic on which odometry is published

goal_blackboard_id

Type	Default
string	“goal”

Description: Blackboard variable to use to supply the goal to the behavior tree for NavigateToPose. Should match ports of BT XML file.

path_blackboard_id

Type	Default
string	“path”

Description: Blackboard variable to get the path from the behavior tree for NavigateThroughPoses feedback. Should match port names of BT XML file.

goals_blackboard_id

Type	Default
string	“goals”

Description: Blackboard variable to use to supply the goals to the behavior tree for NavigateThroughPoses. Should match ports of BT XML file.

use_sim_time

Type	Default
bool	false

Description: Use time provided by simulation.

error_code_names

Type	Default
vector<string>	[“compute_path_error_code”, “follow_path_error_code”]

Description: List of of error codes to compare.

Example¶

bt_navigator:
  ros__parameters:
    use_sim_time: true
    global_frame: map
    robot_base_frame: base_link
    transform_tolerance: 0.1
    default_nav_to_pose_bt_xml: replace/with/path/to/bt.xml
    default_nav_through_poses_bt_xml: replace/with/path/to/bt.xml
    goal_blackboard_id: goal
    goals_blackboard_id: goals
    path_blackboard_id: path
    navigators: ['navigate_to_pose', 'navigate_through_poses']
    navigate_to_pose:
      plugin: "nav2_bt_navigator/NavigateToPoseNavigator"
    navigate_through_poses:
      plugin: "nav2_bt_navigator/NavigateThroughPosesNavigator"
    plugin_lib_names:
      - nav2_compute_path_to_pose_action_bt_node
      - nav2_follow_path_action_bt_node
      - nav2_back_up_action_bt_node
      - nav2_spin_action_bt_node
      - nav2_wait_action_bt_node
      - nav2_clear_costmap_service_bt_node
      - nav2_is_stuck_condition_bt_node
      - nav2_goal_reached_condition_bt_node
      - nav2_initial_pose_received_condition_bt_node
      - nav2_goal_updated_condition_bt_node
      - nav2_reinitialize_global_localization_service_bt_node
      - nav2_rate_controller_bt_node
      - nav2_distance_controller_bt_node
      - nav2_speed_controller_bt_node
      - nav2_recovery_node_bt_node
      - nav2_pipeline_sequence_bt_node
      - nav2_round_robin_node_bt_node
      - nav2_transform_available_condition_bt_node
      - nav2_time_expired_condition_bt_node
      - nav2_distance_traveled_condition_bt_node
      - nav2_single_trigger_bt_node
    error_code_names:
      - compute_path_error_code
      - follow_path_error_code
      # - smoother_error_code, navigate_to_pose_error_code, navigate_through_poses_error_code, etc