ROS 2 Launch System

The ROS 2 Launch system

Content Outline

    Introduction

    You are using python to define a description of “actions”, but do not confuse it with action server or clients

    Frontents

    • Python
    • XML
    • YAML

    The Bare Minimum

    bare.launch.py
    from launch import LaunchDescription

def generate_launch_description() -> LaunchDescription:

    ld = LaunchDescription()

    return ld

    Launch “Actions”

    # List of all Launch Actions for Humble and Jazzy
# from source: https://raw.githubusercontent.com/ros2/launch/humble/launch/launch/actions/__init__.py
__all__ = [
    'AppendEnvironmentVariable',
    'DeclareLaunchArgument',
    'EmitEvent',
    'ExecuteLocal',
    'ExecuteProcess',
    'GroupAction',
    'IncludeLaunchDescription',
    'LogInfo',
    'OpaqueCoroutine',
    'OpaqueFunction',
    'PopEnvironment',
    'PopLaunchConfigurations',
    'PushEnvironment',
    'PushLaunchConfigurations',
    'ResetEnvironment',
    'ResetLaunchConfigurations',
    'RegisterEventHandler',
    'SetEnvironmentVariable',
    'SetLaunchConfiguration',
    'Shutdown',
    'TimerAction',
    'UnregisterEventHandler',
    'UnsetEnvironmentVariable',
    'UnsetLaunchConfiguration',
]
    minimal.launch.py
    from launch import LaunchDescription
from launch.actions import LogInfo

def generate_launch_description() -> LaunchDescription:

    ld = LaunchDescription()

    ld.add_action(
        LogInfo(msg="Hello Launch")
    )

    return ld

    ROS Launch Actions

    Node
ComposableNodeContainer
LoadComposableNodes
LifecycleNode
LifecycleTransition
PushROSNamespace
ROSTimer
SetParameter
SetParametersFromFile
SetRemap
SetROSLogDir
SetUseSimTime

    Reminder:

    ros2 run <package> <executable> <arguments> --ros-args <ros_arguments> -r <remap from `remappings`> -p <param from `parameters`>
    launch_ros.actions.Node(
    package="<package>",
    executable="<executable>"
    exec_name="os_level_process_name"      # defaults to basename of executable
    name="<node_name>"                     # -r (--remap) __node:=<node_name>
    namespace="<your_namespace>",          # -r (--remap) __ns:=/<your_namespace> (the `/` is important)
    arguments=[                            # executable level arguments (if your executable supports them)
      "--config", "/tmp/my.cfg",
      "--rate", "20"
    ]
    ros_arguments=[                        # literally mirror `--ros-args` in the CLI
        "-r", "__ns:=/your_namespace",
        "--log-level", "warn",
        "--enclave", "/fully/qualified/path"
    ],
    parameters=[                           # these are node level parameters. Keep in mind that node parameters are typed
      {"node_param": <typed_value>},       # -p (--param) node_parameter:=<typed_value>
      "/path/with/node_parameter.yaml"     # you can pass path to a yaml file with node parameters
      {"other_param": <typed_value>},      # this `other_param` override the one in yaml (if used after it)
    ],
    remappings=[                           # you can remap anything. Due to name-resolution process, you can:
                                           # topics, services, actions, parameters, node name, namespace
      ('/some_topic', '/some_other_name'), # the full path resolution is /<namespace>/<your_remapping>
    ]
)

    External Resources