examaple.launch.py
| # example.launch.py import os from ament_index_python import get_package_share_directory from launch import LaunchDescription from launch.actions import DeclareLaunchArgument from launch.actions import IncludeLaunchDescription from launch.actions import GroupAction from launch.launch_description_sources import PythonLaunchDescriptionSource from launch.substitutions import LaunchConfiguration from launch.substitutions import TextSubstitution from launch_ros.actions import Node from launch_ros.actions import PushRosNamespace def generate_launch_description(): # args that can be set from the command line or a default will be used background_r_launch_arg = DeclareLaunchArgument( "background_r", default_value=TextSubstitution(text="0") ) background_g_launch_arg = DeclareLaunchArgument( "background_g", default_value=TextSubstitution(text="255") ) background_b_launch_arg = DeclareLaunchArgument( "background_b", default_value=TextSubstitution(text="0") ) chatter_ns_launch_arg = DeclareLaunchArgument( "chatter_ns", default_value=TextSubstitution(text="my/chatter/ns") ) # include another launch file launch_include = IncludeLaunchDescription( PythonLaunchDescriptionSource( os.path.join( get_package_share_directory('demo_nodes_cpp'), 'launch/topics/talker_listener.launch.py')) ) # include another launch file in the chatter_ns namespace launch_include_with_namespace = GroupAction( actions=[ # push-ros-namespace to set namespace of included nodes PushRosNamespace(LaunchConfiguration('chatter_ns')), IncludeLaunchDescription( PythonLaunchDescriptionSource( os.path.join( get_package_share_directory('demo_nodes_cpp'), 'launch/topics/talker_listener.launch.py')) ), ] ) # start a turtlesim_node in the turtlesim1 namespace turtlesim_node = Node( package='turtlesim', namespace='turtlesim1', executable='turtlesim_node', name='sim' ) # start another turtlesim_node in the turtlesim2 namespace # and use args to set parameters turtlesim_node_with_parameters = Node( package='turtlesim', namespace='turtlesim2', executable='turtlesim_node', name='sim', parameters=[{ "background_r": LaunchConfiguration('background_r'), "background_g": LaunchConfiguration('background_g'), "background_b": LaunchConfiguration('background_b'), }] ) # perform remap so both turtles listen to the same command topic forward_turtlesim_commands_to_second_turtlesim_node = Node( package='turtlesim', executable='mimic', name='mimic', remappings=[ ('/input/pose', '/turtlesim1/turtle1/pose'), ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'), ] ) return LaunchDescription([ background_r_launch_arg, background_g_launch_arg, background_b_launch_arg, chatter_ns_launch_arg, launch_include, launch_include_with_namespace, turtlesim_node, turtlesim_node_with_parameters, forward_turtlesim_commands_to_second_turtlesim_node, ]) |
turtlesim_mimic_launch.py
| from launch import LaunchDescription from launch_ros.actions import Node def generate_launch_description(): return LaunchDescription([ Node( package='turtlesim', namespace='turtlesim1', executable='turtlesim_node', name='sim' ), Node( package='turtlesim', namespace='turtlesim2', executable='turtlesim_node', name='sim' ), Node( package='turtlesim', executable='mimic', name='mimic', remappings=[ ('/input/pose', '/turtlesim1/turtle1/pose'), ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'), ] ) ]) |
example_main.launch.py
| from launch_ros.substitutions import FindPackageShare from launch import LaunchDescription from launch.actions import IncludeLaunchDescription from launch.launch_description_sources import PythonLaunchDescriptionSource from launch.substitutions import PathJoinSubstitution, TextSubstitution def generate_launch_description(): colors = { 'background_r': '200' } return LaunchDescription([ IncludeLaunchDescription( PythonLaunchDescriptionSource([ PathJoinSubstitution([ FindPackageShare('launch_tutorial'), 'launch', 'example_substitutions.launch.py' ]) ]), launch_arguments={ 'turtlesim_ns': 'turtlesim2', 'use_provided_red': 'True', 'new_background_r': TextSubstitution(text=str(colors['background_r'])) }.items() ) ]) |
example_substitutions.launch.py
| from launch_ros.actions import Node from launch import LaunchDescription from launch.actions import DeclareLaunchArgument, ExecuteProcess, TimerAction from launch.conditions import IfCondition from launch.substitutions import LaunchConfiguration, PythonExpression def generate_launch_description(): turtlesim_ns = LaunchConfiguration('turtlesim_ns') use_provided_red = LaunchConfiguration('use_provided_red') new_background_r = LaunchConfiguration('new_background_r') turtlesim_ns_launch_arg = DeclareLaunchArgument( 'turtlesim_ns', default_value='turtlesim1' ) use_provided_red_launch_arg = DeclareLaunchArgument( 'use_provided_red', default_value='False' ) new_background_r_launch_arg = DeclareLaunchArgument( 'new_background_r', default_value='200' ) turtlesim_node = Node( package='turtlesim', namespace=turtlesim_ns, executable='turtlesim_node', name='sim' ) spawn_turtle = ExecuteProcess( cmd=[[ 'ros2 service call ', turtlesim_ns, '/spawn ', 'turtlesim/srv/Spawn ', '"{x: 2, y: 2, theta: 0.2}"' ]], shell=True ) change_background_r = ExecuteProcess( cmd=[[ 'ros2 param set ', turtlesim_ns, '/sim background_r ', '120' ]], shell=True ) change_background_r_conditioned = ExecuteProcess( condition=IfCondition( PythonExpression([ new_background_r, ' == 200', ' and ', use_provided_red ]) ), cmd=[[ 'ros2 param set ', turtlesim_ns, '/sim background_r ', new_background_r ]], shell=True ) return LaunchDescription([ turtlesim_ns_launch_arg, use_provided_red_launch_arg, new_background_r_launch_arg, turtlesim_node, spawn_turtle, change_background_r, TimerAction( period=2.0, actions=[change_background_r_conditioned], ) ]) |
References
[1] https://docs.ros.org/en/foxy/How-To-Guides/Launch-file-different-formats.html
Using Python, XML, and YAML for ROS 2 Launch Files — ROS 2 Documentation: Foxy documentation
You're reading the documentation for an older, but still supported, version of ROS 2. For information on the latest version, please have a look at Humble. Using Python, XML, and YAML for ROS 2 Launch Files ROS 2 launch files can be written in Python, XML,
docs.ros.org
[2] https://docs.ros.org/en/humble/Tutorials/Intermediate/Launch/Creating-Launch-Files.html
Creating a launch file — ROS 2 Documentation: Humble documentation
To launch turtlesim_mimic_launch.py, enter into the directory you created earlier and run the following command: Note It is possible to launch a launch file directly (as we do above), or provided by a package. When it is provided by a package, the syntax i
docs.ros.org
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