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6.ROS2 node
6. ROS2 Nodes
1. Node Introduction
Regardless of the communication method used, the construction of communication objects relies on nodes. In ROS2, each node generally corresponds to a single functional module (for example, a radar driver node might be responsible for publishing radar messages, while a camera driver node might be responsible for publishing image messages). A complete robotic system may consist of many nodes working together. In ROS2, a single executable file (C++ program or Python program) can contain one or more nodes.
2. Node Creation Process
- Create a Program File
- Import Related ROS Libraries
- Write Node Functions
- Write the Configuration File
- Compile and Run
3. Hello World Node Example
This section uses the Python package as an example.
3.1. Creating the Python Package
Replace -workspace with your actual workspace path.
xxxxxxxxxxcd workspace/srcros2 pkg create pkg_helloworld_py --build-type `ment_python` --dependencies `rclpy` --node-name `helloworld`3.2. Writing Code
Executing the above command will create pkg_helloworld_py and a helloworld.py file for writing the node:
Delete the original helloworld.py Write the following code:
xxxxxxxxxximport rclpy # ROS2 Python interface libraryfrom rclpy.node import Node # ROS2 node classimport time"""Create a HelloWorld node and log "Hello World" during initialization."""class HelloWorldNode(Node): def __init__(self, name): super().__init__(name) # Initialize the ROS2 node parent class while rclpy.ok(): # Check if the ROS2 system is running properly self.get_logger().info("Hello World") # Output ROS2 logs time.sleep(0.5) # Sleep control loop timedef main(args=None): # Main entry point for the ROS2 node rclpy.init(args=args) # Initialize the ROS2 Python interface node = HelloWorldNode("helloworld") # Create and initialize the ROS2 node object rclpy.spin(node) # Loop and wait for ROS2 to exit. node.destroy_node() # Destroy the node object rclpy.shutdown() # Close the ROS2 Python interfaceAfter writing the code, you need to set the package's compilation options to let the system know the entry point for the Python program. Open the package's setup.py file and add the following entry point configuration:
3.3. Compiling the Package
- Compiling the Package
xxxxxxxxxxcolcon build --packages-select pkg_helloworld_py- Refresh the environment variables in the workspace
xxxxxxxxxxsource install/setup.bash3.4. Running the Node