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5. ROS 2 Function Packages

1. Introduction to Function Packages​

Each robot may have many functions, such as motion control, visual perception, and autonomous navigation. While it is possible to combine all source code into one project, sharing and maintaining such code becomes difficult.

Function packages solve this by separating different functional modules into independent packages. This minimizes coupling and greatly improves code reuse and collaboration within the ROS community.

2. Creating Function Packages​

To create a function package in ROS 2, use the following command format:

ros2 pkg create <package_name> --build-type <build-type> --dependencies <dependencies> --node-name <node-name>

Command Parameter Description​

  • pkg: Operates on ROS 2 packages\
  • create: Creates a new package\
  • package_name: Required, name of the package\
  • build-type: Required
    • ament_cmake → C++ packages\
    • ament_python → Python packages\
  • dependencies: Optional, such as:
    • rclcpp for C++
    • rclpy for Python\
  • node-name: Optional, auto-generates an executable node

Switch to Workspace Source Directory​

Replace workspace with your actual workspace path:

cd workspace/src

Create a C++ Package Example​

ros2 pkg create pkg_helloworld_cpp --build-type ament_cmake --dependencies rclcpp --node-name helloworld

Create a Python Package Example​

ros2 pkg create pkg_helloworld_py --build-type ament_python --dependencies rclpy --node-name helloworld

3. Compile the Package​

After writing code inside the package, compile the workspace:

Compile All Packages​

colcon build

Compile Specific Packages​

colcon build --packages-select pkg1 pkg2

4. Complete Workspace Structure with Feature Packages​

The standard ROS 2 workspace structure is shown below:

WorkSpace
 |--- build        # Build output for each package
 |--- install      # Installed packages
 |--- log          # Build logs
 |--- src          # Source directory
       |-- C++ Package
       |     |-- package.xml
       |     |-- CMakeLists.txt
       |     |-- src
       |     |-- include
       |     |-- msg
       |     |-- srv
       |     |-- action
       |
       |-- Python Package
             |-- package.xml
             |-- setup.py
             |-- setup.cfg
             |-- resource
             |-- test
             |-- <package_name>

Optional Configuration Directories​

Both C++ and Python packages may also include:

|-- launch    # Launch files
|-- rviz      # RViz configurations
|-- urdf      # Robot model files
|-- params    # Parameter files
|-- world     # Simulation environments
|-- map       # Navigation maps
|-- ...

These directories can be customized or extended based on project requirements.