Launch

Overview

The purpose of rosbag2 is to serialize and store data; it is a database.

ros2 launch package_name launch_file_name

ros2 pkg create cpp01_launch --build-type ament_cmake --dependencies rclcpp

ros2 pkg create cpp01_launch --build-type ament_cmake --dependencies rclcpp

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

def generate_launch_description():
    return LaunchDescription([])

Basic Launch Usage Process (C++)

After configuring this, no matter how many launch files are in my launch directory, I only need to configure it once.

This shows that our CMake configuration is correct.

from launch import LaunchDescription
from launch_ros.actions import Node
封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

def generate_launch_description():
    return LaunchDescription([])

<launch>
    <node pkg = "turtlesim" exec = "turtlesim_node" name = "t1" />
    <node pkg = "turtlesim" exec = "turtlesim_node" name = "t2" />
</launch>

launch:
node:
  pkg: "turtlesim"
  exec: "turtlesim_node"
  name: "t1"
node:
  pkg: "turtlesim"
  exec: "turtlesim_node"
  name: "t2"

It's best to add a dependency.

Launch_Python_Node

This is the tag exec_name

The difference in passing these two parameters lies in the --ros-args distinction.

It's simpler to write it in the launch file.

This is equivalent.

The content inside {} is in YAML format.

There is another more common method: read the YAML file first, store all the data in the YAML, and then read it directly when needed.

Place the yaml file in the config folder.

ros2 param dump haha --output-dir src/cpp01_launch/config/

You also need to configure CMakeLists.

We should read the one in the install directory.

Directly copy the path.

The code can be further optimized.

This is used to get the share directory path of a specific package.

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

import os

def generate_launch_description():

    # turtle1 = Node(

    #     package="turtlesim",

    #     executable="turtlesim_node",

    #     exec_name="my_label",

    #     ros_arguments=["--remap","__ns:=/t2"]

    #     )
    turtle2 = Node(
        package="turtlesim",
        executable="turtlesim_node",
        name="haha",
        parameters=[os.path.join(get_package_share_directory("cpp01_launch"),"config","haha.yaml")]
        )
    return LaunchDescription([turtle2])

It is recommended to use the third method: dynamically obtaining the path.

"respawn" means automatic restart. After running a node with this setting, if you close the Little Turtle window with your mouse, the node will automatically restart and open a new Little Turtle window.

Press Ctrl+C to terminate.

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

import os

def generate_launch_description():

    # turtle1 = Node(

    #     package="turtlesim",

    #     executable="turtlesim_node",

    #     exec_name="my_label",

    #     ros_arguments=["--remap","__ns:=/t2"]

    #     )
    turtle2 = Node(
        package="turtlesim",
        executable="turtlesim_node",
        name="haha",

        # parameters=[{"background_r": 255,"background_g": 0,"background_b": 0}],

        # parameters=["/home/tungchiahui/mysource/ros2src/4.ws02_tools/install/cpp01_launch/share/cpp01_launch/config/haha.yaml"],
        parameters=[os.path.join(get_package_share_directory("cpp01_launch"),"config","haha.yaml")],
        respawn=True
        )
    return LaunchDescription([turtle2])

The first is the original topic name, the second is the new topic name.

Launch_Python_Execute Command

This is a list containing our instructions.

This outputs logs to both the terminal and the log file; if omitted, logs will only be written to the file.

This treats the command as a terminal instruction to execute.

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

def generate_launch_description():
    turtle = Node(
        package="turtlesim",
        executable="turtlesim_node"
    )
    cmd = ExecuteProcess(
        cmd = ["ros2 topic echo /turtle1/pose"],
        output = "both",
        shell = True
    )

    return LaunchDescription([turtle,cmd])

If the instruction is too long, it can be split into multiple strings for execution.

This also works.

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

def generate_launch_description():
    turtle = Node(
        package="turtlesim",
        executable="turtlesim_node"
    )
    cmd = ExecuteProcess(
        cmd = [FindExecutable(name="ros2"),"topic","echo","/turtle1/pose"],
        output = "both",
        shell = True
    )

    return LaunchDescription([turtle,cmd])

Launch_Python parameter settings

If no value is passed, the turtle's red color is full, resulting in a pink background.

You can also pass values, such as backg_r:=0.

This makes the background color shift more towards blue-green.

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

def generate_launch_description():

    bg_r = DeclareLaunchArgument(name="backg_r",default_value="255")
    bg_g = DeclareLaunchArgument(name="backg_g",default_value="255")
    bg_b = DeclareLaunchArgument(name="backg_b",default_value="255")
    turtle = Node(
        package="turtlesim",
        executable="turtlesim_node",
        parameters=[{"background_r" : LaunchConfiguration("backg_r"),"background_g" : LaunchConfiguration("backg_g"),"background_b" : LaunchConfiguration("backg_b")}]
    )
    return LaunchDescription([bg_r,bg_g,bg_b,turtle])

Launch_Python_File Inclusion

Suppose I want to write a launch file related to robot startup. In this launch file, I may need to start the LiDAR, start the IMU, start the chassis, and so on. We need to include all these launch files into the robot startup launch file.

This value is an object encapsulated from the included launch file.

The class corresponding to this object is PythonLaunchDescriptionSource.

You also need to set a parameter inside the class.

This parameter is launch_file_path, which is the file path.

It is recommended to use this to obtain the path.

You can also pass parameters to it.

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

import os

def generate_launch_description():
    include = IncludeLaunchDescription(
        launch_description_source=PythonLaunchDescriptionSource(
            launch_file_path=os.path.join(
                get_package_share_directory("cpp01_launch"),
                "launch/py",
                "py04_args_launch.py"
            )
        ),
        launch_arguments=[("backg_r","80"),("backg_g","10"),("backg_b","200")]
    )
    return LaunchDescription([include])

Launch_Python_Group Settings

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

def generate_launch_description():
    turtle1 = Node(
    package="turtlesim",
    executable="turtlesim_node",
    name="t1"
    )
    turtle2 = Node(
    package="turtlesim",
    executable="turtlesim_node",
    name="t2"
    )
    turtle3 = Node(
    package="turtlesim",
    executable="turtlesim_node",
    name="t3"
    )

    group1 = GroupAction(actions=[PushRosNamespace("g1"),turtle1,turtle2])
    group2 = GroupAction(actions=[PushRosNamespace("g2"),turtle3])

    return LaunchDescription([group1,group2])

Launch_Python_Event Setting

The first is mainly used to register events, the second is to start events, and the third is for node exit.

This is the command to spawn a new turtle in the terminal.

The first parameter is used to register for which event.

target_action is the event source, and you need to register the event for which node.

on_start is waiting for the event to be triggered — what operations do you need to perform?

from launch import LaunchDescription
from launch_ros.actions import Node

封装终端指令相关类
from launch.actions import ExecuteProcess
from launch.substitutions import FindExecutable
参数声明与获取
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
文件包含相关
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource
分组相关
from launch_ros.actions import PushRosNamespace
from launch.actions import GroupAction
事件相关
from launch.event_handlers import OnProcessStart,OnProcessExit
from launch.actions import ExecuteProcess,RegisterEventHandler,LogInfo
获取功能包下share目录或路径
from ament_index_python.packages import get_package_share_directory

def generate_launch_description():
    turtle = Node(
    package="turtlesim",
    executable="turtlesim_node",
    )
    spawn = ExecuteProcess(
        cmd=["ros2 service call /spawn turtlesim/srv/Spawn \"{'x': 8.0,'y': 3.0}\""],
        output="both",
        shell=True
    )

    event_start = RegisterEventHandler(
        event_handler=OnProcessStart(
            target_action=turtle,
            on_start=spawn
        )
    )

    event_exit = RegisterEventHandler(
        event_handler=OnProcessExit(
            target_action=turtle,
            on_exit=[LogInfo(msg="turtlesim_node:退出！")]
        )
    )
    return LaunchDescription([turtle,event_start,event_exit])

on_exit can create an object, and it can also be placed in a list.

You can just learn the Python version of Launch. It's fine to have a general understanding of the XML and YAML versions of Launch — just write the Python version yourself. When you need to use Launch files from someone else's open-source package, even if they're in XML or YAML format, it generally won't affect normal usage.

Launch_XML_YAML_Node

Launch_XML_YAML_Execute Command

Launch_XML_YAML_Parameter Settings

Launch_XML_YAML_Group Settings

Launch_XML_YAML_file contains