Advanced Launch Configuration

Using the standard ros_bt_py launch file is all you need for designing and executing BTs with the standard bt_py nodes. Utilizing the Package Loader in the GUI you can also extend this to custom Node Classes to enhance your bt_py experience!

While this is nice for development, using BTs in production has other constraints and conditions, such as automatically loading custom node classes or starting a tree on launch.

In general you will want to create a custom package for your launch files, similar to the custom nodes, to keep your ros_bt_py repository clean.

Using Custom Node Classes in a Project

After writing and testing all the node classes needed inside your_awesome_package you will need to include them when launching ros_bt_py to actually use them.

All you need to do is to write a new launch file and overwrite the module_list argument to include your node modules:

from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch_ros.substitutions import FindPackageShare

def generate_module_list():
    module_list = [
        "ros_bt_py.nodes",
        "ros_bt_py.ros_nodes",
        "your_awesome_package.nodes",
    ]
    return str(module_list)

def generate_launch_description():
    ros_bt_py_launch = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            [
                FindPackageShare("ros_bt_py"),
                "/launch",
                "/ros_bt_py.launch.py",
            ]
        ),
        launch_arguments={"node_modules": generate_module_list()}.items(),
    )

    return LaunchDescription(
        [
            ros_bt_py_launch
        ]
    )

Because LaunchDescription only takes strings as launch arguments the custom generate_module_list function is used to allow for adding multiple new modules while also allowing for line breaks for readability.

Other Important Launch Arguments

Other relevant launch arguments you might find useful:

Launch Options

Launch Argument	Description	Default Value	Tip
enable_web_interface	Start web GUI on startup.	False	For working in production the interface is not necessary
load_default_tree	Load the default tree on startup	False	Needs to be set to true to load a tree
default_tree_path	Path to the default tree to load on startup	“”	path to load the tree, can be used with file:// or package://
default_tree_control_command	Command to execute per default after loading the default tree on startup	2	DO_NOTHING = 0, TICK_ONCE = 1, TICK_PERIODICALLY = 2, TICK_UNTIL_RESULT = 3
tree_storage_paths	Specify the storage paths for your trees when using “Save to File”	“[‘$HOME/.ros’]”	Use this to save trees directly to your tree repository