Additional tools to handle topics

You’ve just written a bunch of nodes containing publishers and subscribers. We will now explore how ROS 2 tools can help you do more things with topics.

We will explore the following topics:

• Introspection with rqt_graph
• Introspection and debugging with the ros2 topic command line
• Changing a topic name when starting a node
• Replaying topic data with bags

Introspecting topics with rqt_graph

We used rqt_graph to visualize nodes in Chapter 3. Let’s run it again and see how to introspect the publisher and subscriber we have just created.

First, start both the number_publisher and number_counter nodes (from any package: my_py_pkg or my_cpp_pkg).

Then, start rqt_graph in another Terminal:

$ rqt_graph

If needed, refresh the view a few times and select Nodes/Topics (all). You can also uncheck the Dead sinks box and the Leaf topics box. This will allow you to see topics even if there is just one subscriber...