对ROS 2Launch文件使用Python、XML和YAML [待校准@6162]

ROS 2launch文件可以用Python、XML和YAML编写。本指南展示了如何使用这些不同的格式来完成相同的任务，并讨论了何时使用每种格式。 [待校准@6163]

Launch文件示例 [待校准@6164]

下面是用Python、XML和YAML实现的launch文件。每个launch文件执行以下动作: [待校准@6165]

# 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,
    ])

使用命令行中的Launch文件 [待校准@6174]

Launch [待校准@6175]

上述任何launch文件都可以与 ros2 launch 一起运行。要尝试调用y，您可以创建一个新包并使用 [待校准@6176]

ros2 launch <package_name> <launch_file_name>

或者通过指定launch文件的路径直接运行文件 [待校准@6177]

ros2 launch <path_to_launch_file>

设置参数 [待校准@6178]

要设置传递给launch文件的参数，应使用 “key:= value” 语法。例如，您可以通过以下方式设置 background_r 的值: [待校准@6179]

ros2 launch <package_name> <launch_file_name> background_r:=255

或 [待校准@6180]

ros2 launch <path_to_launch_file> background_r:=255

控制海龟 [待校准@6181]

要测试重新映射是否有效，您可以通过在另一个终端中运行以下命令来控制海龟: [待校准@6182]

ros2 run turtlesim turtle_teleop_key --ros-args --remap __ns:=/turtlesim1

Python、XML或YAML: 我应该使用哪个？ [待校准@6183]

注解

[需手动修复的语法]Launch文件ROS 1写XML，XML最熟悉的可能来自ROS 1。要了解发生了什么变化，您可以访问 迁移launch文件ROS 1ROS 2 [待校准@6189] 。 [待校准@6184]

对于大多数应用，选择哪种ROS 2launch格式取决于开发人员的偏好。但是，如果您的launch文件需要XML或YAML无法实现的灵活性，则可以使用Python编写launch文件。对ROS 2launch使用Python更加灵活，原因有以下两个: [待校准@6185]

  • Python是一种脚本语言，因此您可以在launch文件中利用该语言及其库。 [待校准@6186]

  • [需手动修复的语法] ros2/launch (general launch features) and ros2/launch_ros (ROS 2特定的launch特征) 是用Python编写的，因此您可以更低级地访问可能不会被XML和YAML公开的launch特征。 [待校准@6187]

也就是说，用Python编写的launch文件可能比用XML或YAML编写的文件更复杂、更冗长。 [待校准@6188]