Ros2 learning notes (8) learn the startup file of ros2 from turnlesim

Preface

Study ROS2 Way , Not through learning ROS1 Instead of , because ROS2 Of “ kernel ” differ ROS1, We must seriously start from scratch and learn again .

Ubuntu edition ：20.04

ROS edition ：Foxy

Review of study notes

• ROS2 Learning notes ( One ) Get document
• ubuntu20.04 install ROS2 and ROS1 coexistence
• ROS2 Learning notes ( Two ) from turtlesim Study ROS2 node
• ROS2 Learning notes ( 3、 ... and ) from turtlesim Study ROS2 The theme
• ROS2 Learning notes ( Four ) from turtlesim Study ROS2 service
• ROS2 Learning notes ( 5、 ... and ) from turtlesim Study ROS2 Parameters
• ROS2 Learning notes ( 6、 ... and ) from turtlesim Study ROS2 action
• ROS2 Learning notes ( 7、 ... and ) from turtlesim Study ROS2 Tools for

1.ROS2 Startup file

When we want to start a large project, we need to run multiple nodes at the same time , It's going to be a lot of trouble , If you run a single startup file, you can start the whole system, including all nodes and configurations , It will be very convenient .ROS2 The startup file in has such a function .

2. establish launch file

$ mkdir ros2_ws
$ cd ros2_ws
$ mkdir launch
$ touch launch/turtlesim_mimic_launch.py

Open a new file with a text editor .

3. To write launch file

Write a turtlesim Startup file for package , The goal of this file is to start two turtle simulators , Let one turtle imitate the movement of another turtle , The startup file code is as follows ：

#  introduce ROS2 launch modular 
from launch import LaunchDescription
from launch_ros.actions import Node

#  start-up launch File description 
def generate_launch_description():
    return LaunchDescription([
        #  Start the first turtle Simulator 
        Node(
            package='turtlesim',#  Function package of the node 
            namespace='turtlesim1', #  Namespaces cannot be the same 
            executable='turtlesim_node',#  Indicates the name of the executable file to run 
            name='sim'#  Node name after startup 
        ),
        #  Start the second turtle Simulator 
        Node(
            package='turtlesim',
            namespace='turtlesim2',#  Namespaces cannot be the same 
            executable='turtlesim_node',
            name='sim'
        ),
        #  start-up mimic
        Node(
            package='turtlesim',
            executable='mimic',
            name='mimic',
            # /input/pose The theme is remapped to /turtlesim1/turtle1/pose
            # /output/cmd_vel Topics will be mapped to /turtlesim2/turtle1/cmd_vel
            remappings=[
                ('/input/pose', '/turtlesim1/turtle1/pose'),
                ('/output/cmd_vel', '/turtlesim2/turtle1/cmd_vel'),
            ]
        )
    ])

Through the remapping operation above , It can be seen that mimic Nodes subscribe to turtle1 The location of , Convert into pairs turtle2 The speed command is issued , It can make turtle2 imitation turtle1 Complete the same exercise

4.ros2 launch

The syntax of the startup file is as follows ：

$ ros2 launch <package_name> <launch_file_name>

Start the file to see the effect ：

$ cd launch
$ ros2 launch turtlesim_mimic_launch.py
----
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [turtlesim_node-1]: process started with pid [11714]
[INFO] [turtlesim_node-2]: process started with pid [11715]
[INFO] [mimic-3]: process started with pid [11716]

Open the new terminal and issue the control command of the little turtle to control the movement of the little turtle ：

$ ros2 topic pub -r 1 /turtlesim1/turtle1/cmd_vel geometry_msgs/msg/Twist "{linear: {x: 2.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: -1.8}}"

We can see two turtles on the same road .

5.rqt_graph Tools

Start the new terminal , Use the following command to view the relationships in the node ：

$ rqt_graph

summary

Startup files simplify the startup of complex systems , Use them well .

Reference:

https://docs.ros.org/en/foxy/Tutorials/Launch-Files/Creating-Launch-Files.html

Conclusion

This paper is also based on the author's learning and use experience , Strong subjectivity , If there is anything wrong or unclear , Welcome to leave a message in the comments area ~

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