About behavior tree plugin/nodes in ros2 humble

[lyysl]

I am trying to write my own behavior tree nodes in ros2 humble. I use this repo as example.
I see in demo_parmas.yaml

bt_navigator:
  ros__parameters:
    use_sim_time: True
    global_frame: map
    robot_base_frame: base_link
    odom_topic: /odom
    bt_loop_duration: 10
    default_server_timeout: 20
    # 'default_coverage_bt_xml' uses defaults:
    # opennav_coverage_bt/behavior_tree/navigate_w_basic_complete_coverage.xml
    navigators: ['navigate_complete_coverage']
    navigate_complete_coverage:
      plugin: "opennav_coverage_navigator/CoverageNavigator"
    error_code_names: ["compute_path_error_code", "follow_path_error_code", "compute_coverage_error_code"]
    plugin_lib_names:
      - nav2_follow_path_action_bt_node
      - nav2_rate_controller_bt_node
      - nav2_recovery_node_bt_node
      - nav2_pipeline_sequence_bt_node
      - nav2_round_robin_node_bt_node
      - opennav_compute_complete_coverage_action_bt_node
      - opennav_cancel_complete_coverage_action_bt_node

The default .xml is navigate_w_basic_complete_coverage.xml. I cannot define the .xml by using default_bt_xml_filename: some_path? I try this but it always use the default .xml in nav2. I see you define a function CoverageNavigator::getDefaultBTFilepath in opennav_coverage_navigator/src/coverage_navigator.cpp. Is it neccesary to use this in order to make the behavior tree xml works? Also the package backported_bt_navigator? Is it problems in ros2 humble only?
I am new to ros2 navigation. It would be nice if you could tell me how I can make the custom plugin works.
Thank you.

[SteveMacenski]

That is the default is none other is given. Make sure to check the launch file and remove any remapping present there for the BT XML that may be adding to or overriding the BT XML given in the yaml file (or just specify your BT XML as a launch parameter instead).

The backported BT navigator is for humble only since humble didn't have plugin based navigators at the time needed for this feature.

If you have more questions, checkout docs.nav2.org!