Currently, there are 2 ways of setting the default Behavior Tree XML file:

• Via the commandline-remapping in https://github.com/ros-planning/navigation2/blob/main/nav2_bringup/bringup/launch/tb3_simulation_launch.py#L41 launch
• Via configuration files https://github.com/ros-planning/navigation2/blob/main/nav2_bringup/bringup/params/nav2_params.yaml#L59

Up until now, we haven't had any default set, so the commandline / launch file method gave us a clear way to set a default using the shared file paths to the BT navigator package (since these must be complete filepaths). However, C++ now has this ability and I have a PR coming soon which will use it to set the default behavior tree XML files in BT navigator itself.

As such, I'm looking to simplify our launch files for readability and I'm not sure remapping in this way is even used by any of our users. I'm looking for information from folks if they're OK with me removing the launch configuration in the launch file and have the BT XML file set via the param file parameterization only. This parameterization would need to be the full path to the XML file (as would the commandline setting). However, the BT navigator would also have a reasonable default behavior tree XML set using the ament_cpp_index package to find the nav2_bt_navigator package and its behavior tree files, which it currently does not.

Therefore, if you are not using a custom behavior tree, nothing would change for you as an end user. If you did change the BT, you'd have to do so through the param file.