How can you design and implement ROS messages and services without common pitfalls?

1 Define your message and service types

Before you create your message and service files, you should have a clear idea of what data types and structures you need to exchange between nodes. ROS provides a set of standard message and service types, such as geometry_msgs, sensor_msgs, and std_srvs, that you can use or extend for your application. However, sometimes you may need to define your own custom message and service types, especially if you have complex or domain-specific data. In that case, you should follow the ROS naming conventions and syntax rules for message and service definitions, and document them well for other users.

2 Organize your message and service files

Once you have defined your message and service types, you should organize them in a logical and consistent way. ROS recommends that you create a separate package for your message and service files, and name it with the suffix _msgs or _srvs. This makes it easier to find and reuse your message and service files, and avoid name conflicts with other packages. You should also group your message and service files by functionality or topic, and use subdirectories if needed. For example, you could have a package named my_robot_msgs, with subdirectories for sensor_msgs, action_msgs, and diagnostic_msgs.

3 Generate your message and service headers

After you have created your message and service files, you need to generate the corresponding C++ and Python headers that you can use in your code. ROS provides a tool called rosmsg or rossrv that can help you inspect and generate your message and service headers. You can also use the catkin_make or catkin build commands to automatically generate the headers for all the message and service files in your workspace. However, you need to make sure that you have listed the message and service dependencies correctly in your package.xml and CMakeLists.txt files, and that you have sourced the setup.bash file before using the headers.

4 Use your message and service headers

Finally, you can use your message and service headers in your code to create publishers, subscribers, clients, and servers. ROS provides a set of libraries and tools that make it easy to work with messages and services in C++ and Python. For example, you can use the rospy or roscpp packages to create nodes, the message_filters or tf packages to synchronize or transform messages, and the rosbag or rostopic packages to record or monitor messages. However, there are some best practices and tips you should follow to avoid common pitfalls when using messages and services. These include using consistent units and coordinate frames for your messages, using the appropriate message or service type for your data, using the roslint or roscpp_style_guide packages to check coding style and conventions for message and service headers, utilizing the roscpp_serialization or rospy_message_converter packages to serialize or deserialize messages and services for non-ROS applications or formats, as well as using the rostest or roslaunch packages to test and debug message and service interactions.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?