ros2-hello-world-part-1.md

Part 1 - Preparing the workspace

1. Install needed tools

sudo apt install python3-colcon-common-extensions -y
sudo apt install python3-rosdep2 -y

# !!! NEW Needed Tools !!!
sudo apt install python3-pip
pip install setuptools==58.2.0

2. Create a new directory for your workspace and "change directory" (cd) to it in terminal

• NOTE: The name of the source directory can be anything but we're making it ros2_ws for this tutorial.

mkdir -p ~/ros2_helloworld_ws/src
cd ~/ros2_helloworld_ws/src

3. Download the example starter package

git clone https://github.com/ros/ros_tutorials.git -b humble

4. Resolve dependencies

cd ..
rosdep update
rosdep install -i --from-path src --rosdistro humble -y

5. Build the workspace

colcon build

You'll see a message along the lines of "All required rosdeps installed successfully"

6. In a brand new terminal window, run the following to start up the TurtleSim

cd ~/ros2_helloworld_ws
source install/local_setup.bash
ros2 run turtlesim turtlesim_node

7. In a brand new terminal window, run the following to control the turtle in TurtleSim

cd ~/ros2_helloworld_ws
source install/local_setup.bash
ros2 run turtlesim turtle_teleop_key

Part 2 - Setting up the project

1. Open a new terminal and source the workspace

cd ~/ros2_helloworld_ws
source install/local_setup.bash

2. Create a new package

cd src
ros2 pkg create --build-type ament_python ros2_hello_world

3. Create two files, one for the publisher and one for the subscriber

cd ros2_hello_world
touch ros2_hello_world/talker_node.py
touch ros2_hello_world/listener_node.py

4. Open VSCode within the working directory

code .

5. In talker_node.py, copy and paste the following template code. Fill out both functions below.

import rclpy
from rclpy.node import Node

from std_msgs.msg import String


class TalkerNode(Node):
    def __init__(self):
        super().__init__('talker_node')
        self.publisher = self.create_publisher(String, 'chatter', 10)
        
        timer_period = 1.0
        self.timer = self.create_timer(timer_period, self.timer_callback)

        self.i = 0

    def timer_callback(self):
        message = String()
        message.data = f'Hello World: {self.i}'

        self.publisher.publish(message)
        self.i += 1


def main(args=None):
    rclpy.init(args=args)
    
    # Initialize the node and start it up
    talker_node = TalkerNode()
    rclpy.spin(talker_node)

    # Destroy the node explicitly
    # (optional - otherwise it will be done automatically when the garbage collector destroys the node object)
    talker_node.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

6. In listener_node.py, copy and paste the following template code. Fill out both functions below.

import rclpy
from rclpy.node import Node

from std_msgs.msg import String


class ListenerNode(Node):
    def __init__(self):
        super().__init__('listener_node')
        self.subscription = self.create_subscription(String, 'chatter', self.listener_callback, 10)
    

    def listener_callback(self, msg):
        print(msg.data)


def main(args=None):
    rclpy.init(args=args)
    
    # Initialize the node and start it up
    listener_node = ListenerNode()
    rclpy.spin(listener_node)

    # Destroy the node explicitly
    # (optional - otherwise it will be done automatically when the garbage collector destroys the node object)
    listener_node.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

7. In ros2_hello_world/package.xml, add the following lines underneath <build_type>ament_python</build_type>

<exec_depend>rclpy</exec_depend>
<exec_depend>std_msgs</exec_depend>

8. In ros2_hello_world/setup.py, edit the following lines.

entry_points={
        'console_scripts': [
                'talker = ros2_hello_world.talker_node:main',
                'listener = ros2_hello_world.listener_node:main',
        ],
},

9. Update the ROS package dependencies from your workspace

cd ~/ros2_helloworld_ws
rosdep install -i --from-path src --rosdistro humble -y

10. Build your package

colcon build --packages-select ros2_hello_world

11. In a brand new terminal window, run the following to start up the talker node

cd ~/ros2_helloworld_ws
source install/local_setup.bash
ros2 run ros2_hello_world talker

12. In a brand new terminal window, run the following to start up the listener node

cd ~/ros2_helloworld_ws
source install/local_setup.bash
ros2 run ros2_hello_world listener