Content outline

• Review ROS2 concepts: networking, DDS, micro-ROS, nodes, topics, bags

• Do ROS2 CLI Tools tutorials: 

  • Do Nodes & topics tutorials

  • CLI, gui tools and terminator

  • Launching nodes

  • Logging and bags, bag recording and playback

Video of Workshop 3

The video of the first half of  Workshop 3 is here

The video of the second half of Workshop 3 is here

ROS Concepts

In this segment we discuss the concepts ROS2 is built around, using these pages for reference: https://docs.ros.org/en/humble/Concepts/Basic.html and also tf2 at https://docs.ros.org/en/humble/Concepts/Intermediate/About-Tf2.html

• What is a node? It's a process that communicates with other ROS2 nodes. 

  • The collection of nodes and their communication channels is called the ROS graph: nodes are the vertices, communication channels are the edges that connect vertices. There's a tool to display the graph

  • Look at nodes graphic in Nodes Tutorial here 

• DDS over UDP provides the communication channels. We can configure DDS on a per-channel basis for best effort (like UDP) or guaranteed delivery (like TCP)

• What is pub-sub? One or more nodes publish data to one or more topics. Other nodes subscribe to topics, and receive all the messages via a callback mechanism. Look at Topics tutorial graphic here 

  • Topics have a name and a defined message format (type). One message-type per topic. Message types are typically some collection of ints, floats, and strings

  • /rosout: the ROS console output, similar to output of a collection of backgrounded processes in Unix

• Node architecture is shown below:

• Micro-ROS architecture, and how it relates to ROS2 nodes and topics: https://micro.ros.org/docs/overview/features/

  • Dark blue is specific code for micro-ROS. Light blue is standard code from ROS2

• ROS bags: a file with a record of all the messages that were sent on some collection of topics

  • bags can be replayed

  • bags are typically inspected using tools like rqt and plotjuggler

CLI Cheat Sheet

Note: <Tab> completion is everywhere!

CLI only

• ros2 <command> -h # display help for the command

• ros2 run <package> <node>

• ros2 node list # list the running nodes

• ros2 node info <node_name> # show info (pubs, subs, services etc) for a running node

• ros2 topic list # list the topics that exist

• ros2 topic [echo | info | hz |  pub | type] <topic> # for a topic, echo, display info, display frequency, publish a msg, report msg type

• ros2 interface list # list all messages

• ros2 interface show nav_msgs/msg/Odometry # show the structure of a specific message

• rosclean - a .bashrc alias that cleans the build out of ros2_ws

GUI-related

• rqt

• ros2 run swri_console swri_console

• ros2 run rqt_topic rqt_topic

• ros2 run rqt_<plugin> rqt_plugin # Run an rqt plugin standalone. <plugin> can be topic, graph, msg, publisher reconfig, or others. Use tab-complete to discover them

• rviz2

• ros2 run swri_console swri_console

• ros2 run plotjuggler plotjuggler

Hands On

In this segment we do several of the ROS2 beginner-level  CLI tools tutorials found here: https://docs.ros.org/en/humble/Tutorials/Beginner-CLI-Tools.html

Beginner CLI Tutorials

• Do the Configuring the ROS2 Environment tutorial - 5 min

• Do the Using Turtlesim, ros2 and rqt tutorial - 15 min

• Do the Understanding Nodes tutorial - 10 min

• Do the Understanding Topics tutorial - 20 min

• Do the Using rqt_console to view console logs except use swri_console - 5 min

• Do the Launching Nodes tutorial - 5 min

• Do the Recording and Playing-back Data tutorial. Use rqt_topic to look at important topics while running, and swri-console to monitor console messages. - 10 min

• List all the supported interfaces with ros2 interface list

• Inspect the Odometry message: run ros2 interface show nav_msgs/msg/Odometry

• Plot the X-Y path, and heading and distance to waypoints in Plotjuggler from the bag.

• Future: Inspect the data on critical topics when near a waypoint using rqt_bag