Behavior-Tree Navigator

Source code on Github.

The BT Navigator (Behavior Tree Navigator) module implements the NavigateToPose, NavigateThroughPoses, and other task interfaces. 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.

Make sure to review all parameters for non-default navigator plugins not discussed on this page (e.g. CoverageNavigator or custom additions).

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. This parameter used to be default_bt_xml_filename pre-Galactic. You can use substitution to specify file path like $(find-pkg-share my_package)/behavior_tree/my_nav_to_pose_bt.xml. However, if left empty, the default behavior tree XML will be loaded from the nav2_bt_navigator package.

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. You can use substitution to specify file path like $(find-pkg-share my_package)/behavior_tree/my_nav_through_poses_bt.xml. However, if left empty, the default behavior tree XML will be loaded from the nav2_bt_navigator package.

always_reload_bt_xml

Type	Default
bool	false

Description: Always load the requested behavior tree XML description, regardless of the name of the currently active XML.

plugin_lib_names

Type	Default
vector<string>	[“”]

Description: List of behavior tree node shared libraries. All Nav2 BT libraries are automatically included for you, so this only needs to include your new custom plugins (new to Jazzy).

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.

wait_for_service_timeout

Type	Default
int	1000

Description: Default timeout value (in milliseconds) while Action or Service BT nodes will waiting for acknowledgement from an service or action server on BT initialization (e.g. wait_for_action_server(timeout)). This value will be overwritten for a BT node if the input port “wait_for_service_timeout” is provided.

action_server_result_timeout

Type	Default	Unit
double	900.0	seconds

Description: The timeout value (in seconds) for action servers to discard a goal handle if a result has not been produced. This used to default to 15 minutes in rcl but was changed to 10 seconds in this PR #1012, which may be less than some actions in Nav2 take to run. For most applications, this should not need to be adjusted as long as the actions within the server do not exceed this deadline. This issue has been raised with OSRF to find another solution to avoid active goal timeouts for bookkeeping, so this is a semi-temporary workaround

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.

bond_heartbeat_period

Type	Default
double	0.1

Description: The lifecycle node bond mechanism publishing period (on the /bond topic). Disabled if inferior or equal to 0.0.

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 # or $(find-pkg-share my_package)/behavior_tree/my_nav_to_pose_bt.xml
    default_nav_through_poses_bt_xml: replace/with/path/to/bt.xml # or $(find-pkg-share my_package)/behavior_tree/my_nav_through_poses_bt.xml
    always_reload_bt_xml: false
    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" # In Iron and older versions, "/" was used instead of "::"
    navigate_through_poses:
      plugin: "nav2_bt_navigator::NavigateThroughPosesNavigator" # In Iron and older versions, "/" was used instead of "::"
    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_is_stopped_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