Developing a ROS 2 package

This tutorial will teach you how to create your first ROS 2 application. It is intended for developers who want to learn how to create custom packages in ROS 2, not for people who want to use ROS 2 with its existing packages.

Prerequisites

Creating a package

All ROS 2 packages begin by running the command

ros2 pkg create --license Apache-2.0 <pkg-name> --dependencies [deps]

in your workspace (usually ~/ros2_ws/src).

To create a package for a specific client library:

ros2 pkg create  --build-type ament_cmake --license Apache-2.0 <pkg-name> --dependencies [deps]

You can then update the package.xml with your package info such as dependencies, descriptions, and authorship.

C++ Packages

You will mostly use the add_executable() CMake macro along with

ament_target_dependencies(<executable-name> [dependencies])

to create executable nodes and link dependencies.

To install your launch files and nodes, you can use the install() macro placed towards the end of the file but before the ament_package() macro.

An example for launch files and nodes:

# Install launch files
install(
  DIRECTORY launch
  DESTINATION share/${PROJECT_NAME}
)

# Install nodes
install(
  TARGETS [node-names]
  DESTINATION lib/${PROJECT_NAME}
)

Python Packages

ROS 2 follows Python’s standard module distribution process that uses setuptools. For Python packages, the setup.py file complements a C++ package’s CMakeLists.txt. More details on distribution can be found in the official documentation.

In your ROS 2 package, you should have a setup.cfg file which looks like:

[develop]
script_dir=$base/lib/<package-name>
[install]
install_scripts=$base/lib/<package-name>

and a setup.py file that looks like:

import os
from glob import glob
from setuptools import find_packages, setup

package_name = 'my_package'

setup(
    name=package_name,
    version='0.0.0',
    # Packages to export
    packages=find_packages(exclude=['test']),
    # Files we want to install, specifically launch files
    data_files=[
        # Install marker file in the package index
        ('share/ament_index/resource_index/packages', ['resource/' + package_name]),
        # Include our package.xml file
        (os.path.join('share', package_name), ['package.xml']),
        # Include all launch files.
        (os.path.join('share', package_name, 'launch'), glob(os.path.join('launch', '*launch.[pxy][yma]*'))),
    ],
    # This is important as well
    install_requires=['setuptools'],
    zip_safe=True,
    author='ROS 2 Developer',
    author_email='ros2@ros.com',
    maintainer='ROS 2 Developer',
    maintainer_email='ros2@ros.com',
    keywords=['foo', 'bar'],
    classifiers=[
        'Intended Audience :: Developers',
        'License :: TODO',
        'Programming Language :: Python',
        'Topic :: Software Development',
    ],
    description='My awesome package.',
    license='TODO',
    # Like the CMakeLists add_executable macro, you can add your python
    # scripts here.
    entry_points={
        'console_scripts': [
            'my_script = my_package.my_script:main'
        ],
    },
)

Combined C++ and Python Packages

When writing a package with both C++ and Python code, the setup.py file and setup.cfg file are not used. Instead, use ament_cmake_python.