[ROS Q&A] 225 – Setup your ROS2 Workspace with Unlimited Node Files

Written by Marco Arruda

29/12/2021

In this post it will be shown how to organize your ROS2 package in such manner that allows you to have as many python scripts as you need. It is a quite simple way of doing it, but can be confusing for those who are coming from ROS 1. Let’s check it out!

Configuring environment

In order to do that in a way anyone can reproduce, let’s use the App of TheconstructSim. Start by creating a new rosject here

After creating it, just hit the Run button and wait for the desktop environment to get ready.

 

Create the ROS package

With the environment ready, create a new ROS 2 package inside the given workspace. Use the commands below:

cd ~/ros2_ws/src
ros2 pkg create --build-type ament_python pkg1 --dependencies rclpycies rclpy 

You must have the package created like in the image below:

 

Create the script files

Create the first script files you want to have in your package:

cd ~/ros2_ws/src

touch pkg1/pkg1/hello_world.py
chmod +x pkg1/pkg1/hello_world.py

touch pkg1/pkg1/goodbye_world.py
chmod +x pkg1/pkg1/goodbye_world.py

You must be able to edit the files from the IDE at this point:

Go to the root workspace:

  • Compile the package
  • Source the workspace
  • Check that your package is added to ROS environment
cd ~/ros2_ws
colcon build

source install/setup.bash

ros2 pkg list | grep pkg1

 

Add some code to the scripts to have some nodes

Add the code below to the hello_world.py script:

import rclpy
from rclpy.node import Node

class MyNode(Node):
    def __init__(self):
        # call super() in the constructor in order to initialize the Node object
        # the parameter we pass is the node name
        super().__init__('hello_world')
        # create a timer sending two parameters:
        # - the duration between 2 callbacks (0.2 seeconds)
        # - the timer function (timer_callback)
        self.create_timer(0.2, self.timer_callback)
        
    def timer_callback(self):
        # print a ROS2 log on the terminal with a great message!
        self.get_logger().info("Hello World!")

def main(args=None):
    # initialize the ROS communication
    rclpy.init(args=args)
    # declare the node constructor
    node = MyNode()
    # pause the program execution, waits for a request to kill the node (ctrl+c)
    rclpy.spin(node)
    # shutdown the ROS communication
    rclpy.shutdown()

if __name__ == '__main__':
    main()

And the same for the goodbye_world.py, just changing the info text

import rclpy
from rclpy.node import Node

class MyNode(Node):
    def __init__(self):
        # call super() in the constructor in order to initialize the Node object
        # the parameter we pass is the node name
        super().__init__('hello_world')
        # create a timer sending two parameters:
        # - the duration between 2 callbacks (0.2 seeconds)
        # - the timer function (timer_callback)
        self.create_timer(0.2, self.timer_callback)
        
    def timer_callback(self):
        # print a ROS2 log on the terminal with a great message!
        self.get_logger().info("Goodbye World!")

def main(args=None):
    # initialize the ROS communication
    rclpy.init(args=args)
    # declare the node constructor
    node = MyNode()
    # pause the program execution, waits for a request to kill the node (ctrl+c)
    rclpy.spin(node)
    # shutdown the ROS communication
    rclpy.shutdown()

if __name__ == '__main__':
    main()

 

Create a launch file

In order to run both scripts at the same time, let’s create a launch file:

cd ~/ros2_ws/src
touch pkg1/launch/hello_goodbye.launch
chmod +x pkg1/launch/hello_goodbye.launch

Add the following content:

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='pkg1',
            executable='hello_world',
            output='screen'),
        Node(
            package='pkg1',
            executable='goodbye_world',
            output='screen'),
    ])

 

Configure the setup.py of the package

In order to add the launch file to the setup, it must contain some libraries like os and glob. The content of the file ~/ros2_ws/src/pkg1/setup.py will look like below:

from setuptools import setup
import os
from glob import glob

package_name = 'pkg1'

setup(
    name=package_name,
    version='0.0.0',
    packages=[package_name],
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
        (os.path.join('share', package_name), glob('launch/*.launch.py'))
    ],
    install_requires=['setuptools'],
    zip_safe=True,
    maintainer='user',
    maintainer_email='user@todo.todo',
    description='TODO: Package description',
    license='TODO: License declaration',
    tests_require=['pytest'],
    entry_points={
        'console_scripts': [
            'hello_world = pkg1.hello_world:main',
            'goodbye_world = pkg1.goodbye_world:main'
        ],
    },
)

 

Compile and run

Compile the package once more and run the launch file

cd ~/ros2_ws
colcon build

source install/setup.bash

ros2 launch pkg1 hello_goodbye.launch.py

The expected result is in the image below:

 

Related courses & material:

Topics:
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