ROS2入门，launch文件解析（同时启动多个节点）_launchdescription

1.launch文件实例：

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'),
            ]
        )
    ])

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首先：固定部分，不必多言

from launch import LaunchDescription
from launch_ros.actions import Node
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接下来是launch文件起始的描述：

def generate_launch_description():
   return LaunchDescription([

   ])
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某一个节点node：

Node(
    package='turtlesim',
    namespace='turtlesim1',
    executable='turtlesim_node',
    name='sim'
),
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namespace：命名空间，只要命名空间不同，就不存在节点名或话题的冲突。
package:节点所在的功能包
executable:功能包内要运行的可执行文件名
name:启动后的节点名

最后一个节点：

Node(
    package='turtlesim',
    node_executable='mimic',
    name='mimic',
    remappings=[
      ('/input/pose', '/turtlesim1/turtle1/pose'),
      ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),
    ]
)

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remapping:重映射，mimic的输入话题从/input/pose重映射为/turtlesim1/turtle1/pose，输出话题从/output/cmd_vel重映射为/turtlesim2/turtle1/cmd_vel。我们基本可以猜到，mimic节点通过订阅turtle1的位置（重映射为/turtlesim1/turtle1/pose），转换成对turtle2的速度指令（充盈设为/turtlesim2/turtle1/cmd_vel）发布出去，最后应该可以达到让turtle2模仿turtle1完成同样的运动。

可考虑用于加载多个机器人。