Midterm Study Guide

[cmurray3]

We will talk about the midterm exam in class on March 14.

In the meantime, here is an outline of what you can expect on the exam:

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ROS Overview

• What is ROS?
• Which version of ROS are we running?
• Which version of Ubuntu?
• How to start ROS?
  • roscore vs roslaunch
• Environment Variables
  • What are they?
  • Which ones do you need?
  • Where do we save them?
• What is the "Parameter Server"?

Packages

• Understand the elements of a ROS package. For example:
  • Nodes, msg, srv, CMakeLists.txt, Package.xml, launch, worlds
• How to create a new package

  cd ~/catkin_ws/src
  catkin_create_pkg
  

• How to compile a package

  cd ~/catkin_ws
  catkin_make
  

• When do you need to compile a package?
• Which files need to be made "executable"? How do we do that?

Nodes

• Nodes are C++ or Python scripts
• Where do you save these in a package?
• What line needs to go at the top of your .py files? Why?
• How to change permissions on .py scripts?
• Different nodes communicate via topics, services, and actions.
• How to run a single node?
• How to run nodes via a launch file?
• How can you tell what nodes are active right now?

Topics

• .msg structure
• What are the available data types?
• How to publish in Python script?
• How to publish from the command line?
• How to subscribe?
• How to create custom topics?
  • What role does CMakeLists.txt play?
  • When do we need to recompile the package?
• How can you tell what topics are being published right now?

Services

• .srv structure
• Difference between Topic and Service?
• What are the available data types?
• How to define server?
• How to call server?
• How server issues response
• How to create custom services.
  • What role does CMakeLists.txt play?
  • When do we need to recompile the package?
• Call a service from the command line (see Gazebo examples)
• How can you tell what services are available right now?

Actions

• What are "actions"?
• How do these differ from topics/services?
• When would these be useful?

Gazebo

• What is Gazebo? Are ROS and Gazebo the same?
• Which version of Gazebo are we running?
• How to launch Gazebo via roslaunch?
• What is a .world file
• What is a .urdf? .sdf? .xacro?
• How to define parameters?
• Where to save .launch files? .world files? Model files?
• What existing 3D models are available?
• Namespaces (multi-robot simulation)

RViz

• What is RViz?
• How to call via launch file?

Other Libraries/Utilities

• tf
• rqt
• rosgraph

Some nice resources to further your understanding

• https://foxglove.dev/blog/the-building-blocks-of-ros1
• A 5-part video series describing the early days of ROS and Gazebo: https://www.redhat.com/en/open-source-stories/robots/breaking-the-wheel
  • A follow-on blog post from one of the authors of our textbook (featured in the above video series): https://www.redhat.com/en/blog/rise-robot-operating-system

[cmurray3]

I've added some supplementary materials to help with your exam prep:

• Textbook Chapter 2: Preliminaries

  • https://wiki.ros.org/ROS/Tutorials/NavigatingTheFilesystem

• Textbook Chapter 3: Topics

  • https://wiki.ros.org/ROS/Tutorials/UnderstandingNodes
  • https://wiki.ros.org/ROS/Tutorials/UnderstandingTopics
  • https://wiki.ros.org/ROS/Tutorials/WritingPublisherSubscriber%28python%29
  • https://wiki.ros.org/ROS/Tutorials/ExaminingPublisherSubscriber

• Textbook Chapter 4: Services

  • https://wiki.ros.org/ROS/Tutorials/UnderstandingServicesParams
  • https://wiki.ros.org/ROS/Tutorials/WritingServiceClient%28python%29
  • https://wiki.ros.org/ROS/Tutorials/ExaminingServiceClient

• Textbook Chapter 5: Actions