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Workspace and Packages

A ROS 2 workspace is a directory on your filesystem where you can store, build, and manage your ROS 2 packages. It's the central place for developing your robot applications.

Colcon: The Build System​

colcon is the primary build tool for ROS 2. It's a command-line tool that automates the process of building, testing, and installing multiple packages in a workspace. colcon is designed to be flexible and extensible, supporting various build types (e.g., ament_cmake, ament_python).

Creating a Workspace​

To create a new ROS 2 workspace, you typically follow these steps:

  1. Create the workspace directory:

    mkdir -p ~/ros2_ws/src

    The src subdirectory is where your source packages will reside.

  2. Navigate into the workspace:

    cd ~/ros2_ws

Packages​

A package is the fundamental unit of organization in ROS 2. It contains source code, build scripts, configuration files, and other resources that together provide a specific functionality (e.g., a driver for a sensor, an algorithm for path planning, or a set of launch files).

Every ROS 2 package must contain a package.xml file, which provides metadata about the package (name, version, description, dependencies, maintainers).

Creating a New Package​

You can create a new ROS 2 package using the ros2 pkg create command. This command generates a basic package structure with necessary files.

For a Python package:

cd ~/ros2_ws/src
ros2 pkg create --build-type ament_python my_robot_controller

For a C++ package:

cd ~/ros2_ws/src
ros2 pkg create --build-type ament_cmake my_sensor_driver

Building a Workspace​

After adding or modifying packages in your workspace, you need to build them using colcon:

cd ~/ros2_ws
colcon build

This command compiles your code, generates executables, and installs necessary files into the install directory within your workspace.

Sourcing the Setup Files​

To use the executables and libraries from your workspace, you need to source the setup files generated by colcon. This adds your workspace's environment variables to your shell.

# In your ~/ros2_ws directory
source install/setup.bash  # For bash/zsh
# source install/setup.ps1 # For PowerShell

It's common practice to source the main ROS 2 installation first, and then your workspace setup files, to ensure your workspace's packages take precedence.

Overlays​

ROS 2 workspaces can be overlaid. This means you can build a new workspace on top of an existing one (e.g., your development workspace on top of your main ROS 2 installation). This allows you to work on specific packages without rebuilding the entire ROS 2 distribution.

The workspace model with colcon and packages promotes modularity, reusability, and efficient development workflows in ROS 2.