ENPM702: ROS Programming L10 Quiz

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Questions and Answers

What is a key aspect of spinning a Node in ROS?

It allows the node to send messages to multiple topics

It makes the node run in the background without interruptions

It keeps the node responsive and operational (correct)

It prevents resource conflicts with other nodes

Which programming paradigm is emphasized when writing a Node with OOP in ROS?

Object-oriented programming (correct)

Event-driven programming

Functional programming

Procedural programming

What is the purpose of a callback in a ROS Node?

To schedule new tasks for the node

To shut down the Node gracefully

To handle incoming messages or events (correct)

To initialize the Node

What does the term 'create_wall_timer' in ROS refer to?

A scheduling function that calls a callback at specified intervals Signup and view all the answers

Which option best describes a Node in the context of ROS?

A process that performs computation and communicates with other nodes Signup and view all the answers

Why is it important to understand how to write a basic ROS Node?

To enable customized functionalities in robotic applications Signup and view all the answers

In ROS, which component primarily enables nodes to send and receive messages?

Topic Signup and view all the answers

What does the schedule function in ROS primarily help to achieve?

It manages the execution timing of callbacks Signup and view all the answers

What is the purpose of the class FirstNode in the given code?

To create a ROS2 node with OOP principles. Signup and view all the answers

What method is called to initialize the ROS2 environment in main.cpp?

rclcpp::init() Signup and view all the answers

What does the RCLCPP_INFO_STREAM() function do in the FirstNode constructor?

Prints an informational message to the console. Signup and view all the answers

Which command is used to build and install the executable for the first_package?

colcon build --packages-select first_package Signup and view all the answers

What is the primary purpose of the rcutils logging system in ROS 2?

To output messages with various severity levels. Signup and view all the answers

Which command is used to build a ROS 2 package?

colcon build Signup and view all the answers

In CMakeLists.txt, what does 'include_directories(include)' specify?

The directory for header files. Signup and view all the answers

Which logging macro would you use to report a critical issue that must be addressed immediately?

RCLCPP_FATAL Signup and view all the answers

What is the purpose of the 'ament_target_dependencies()' function in CMakeLists.txt?

To link the target with specified dependencies. Signup and view all the answers

Which statement about the current FirstNode class is true?

It inherits from rclcpp::Node. Signup and view all the answers

What is the effect of calling `rclcpp::init(argc, argv)` in a ROS 2 program?

It destroys global resources created during the original call. Signup and view all the answers

What does 'spinning a node' refer to in ROS 2?

Keeping a node actively running to process callbacks. Signup and view all the answers

What would happen if you forget to call 'rclcpp::shutdown()' in main.cpp?

The node might continue running indefinitely. Signup and view all the answers

Which severity level in logging would be appropriate for general informational messages?

RCLCPP_INFO Signup and view all the answers

Which line in CMakeLists.txt correctly adds an executable for building in ROS 2?

add_executable(hello src/main.cpp) Signup and view all the answers

In a ROS 2 program, after editing CMakeLists.txt, what must you do next to complete the build?

Source the local workspace. Signup and view all the answers

What is the primary role of a node in ROS 2?

To execute a simple task or process Signup and view all the answers

What is the purpose of the `rclcpp::init(argc, argv)` function?

To initialize global resources for middleware and client library Signup and view all the answers

What happens when rclcpp::spin() is called in a ROS 2 node?

It blocks execution and keeps the node alive. Signup and view all the answers

What command is used to run the node after it has been built?

ros2 run first_package hello Signup and view all the answers

What does the statement `RCLCPP_INFO_STREAM(node->get_logger(), 'Hello');` achieve?

It logs the message 'Hello' for debugging purposes. Signup and view all the answers

What signal is handled when Ctrl + C is pressed?

SIGINT Signup and view all the answers

Which function is automatically called to perform cleanup when Ctrl + C is detected?

rclcpp::shutdown() Signup and view all the answers

What is the significance of the `rclcpp::shutdown()` function?

It invalidates all nodes and their constituent parts. Signup and view all the answers

Which of the following statements about publishers in ROS 2 is true?

A node can act as both publisher and subscriber. Signup and view all the answers

What is the main purpose of calling rclcpp::shutdown()?

To release resources and terminate nodes. Signup and view all the answers

Which command compiles a specific ROS 2 package?

colcon build --packages-select first_package Signup and view all the answers

When writing a publisher in ROS 2, what kind of message structure is typically used?

A message structure like geometry_msgs/msg/Twist Signup and view all the answers

What is a crucial aspect of object-oriented programming (OOP) in developing complex ROS 2 nodes?

Creating intricate structures with methods and attributes. Signup and view all the answers

Which of the following steps is NOT part of the process to spin a node?

Initialize the node with ros2 init Signup and view all the answers

What does spinning a node with rclcpp::spin() achieve in a ROS 2 application?

It continuously processes events and callbacks. Signup and view all the answers

What is a callback function used for in programming?

To execute a function at a specified point during another function's execution Signup and view all the answers

What command is used to visualize messages published to /cmd_vel?

ros2 interface show Signup and view all the answers

What is the primary purpose of a function pointer?

To hold the address of a function and call it via the pointer Signup and view all the answers

In the example provided, how is the function 'add' invoked through the pointer 'ptr'?

Using the dereference operator Signup and view all the answers

What issue might be encountered when spawning the Turtlebot in RViz?

The robot model may not be displayed correctly Signup and view all the answers

Which function is used to move the robot around using the keyboard?

ros2 run turtlebot3_teleop teleop_keyboard Signup and view all the answers

In the example provided, what will the line 'int result_direct = ptr(5, 10);' accomplish?

It will call the add function through the pointer Signup and view all the answers

What type of argument is typically passed to a function in a callback?

Any callable or function reference Signup and view all the answers

Study Notes

ENPM702: Introductory Robot Programming L10: ROS (Part 2)

Course: ENPM702, Introductory Robot Programming
Section: L10, ROS (Part 2)
Version: 2.0
Lecturer: Z. Kootbally
School: University of Maryland
Semester/Year: Fall 2024
Date: 2024/11/12

Learning Objectives
Node
- Writing a Node
- Spinning a Node
- Writing a Node with OOP
Turtlebot
- Velocity
- Packages
- Spawn
- Teleoperation
Callbacks
- Callables
ROS Scheduling
- create_wall_timer
Next Class
Appendix A

Changelog

v2.0: Added sections on callbacks and ROS scheduler.
v1.0: Original version.

Convention

General
ROS
- File
- Folder
- Link
- Command
- Example
- Terminology
Syntax
Important notes
Best practices
Question
Node
Topic
Message
Warning
Summary
Tips

Learning Objectives

Write a Node: Understand how to create a basic ROS 2 node and implement it in code.
Spinning a Node: Learn the importance and process of spinning a node to keep it responsive and operational.
Write a Node with OOP: Implement nodes using object-oriented programming principles to manage more complex structures and functionalities.
Publishers: Understand the concept of publishers in ROS 2 and how to create them
Messages and Topics: Gain knowledge about message structures and how data is transmitted through topics.
Write a Publisher: Learn to write and implement a publisher in ROS 2 to control robot actions, including publishing specific data types like geometry_msgs/msg/Twist.

Node - Part I

A node is a small program that executes a simple task or process.
Nodes can publish data (publishers), receive data (subscribers), or do both (publishers/subscribers).

Node - Write a Node

Create a node in first_package/src/main.cpp that prints "Hello" to the terminal.
Using CMakeLists.txt to build and install the executable.
- cd ~/ros702_ws
- colcon build --packages-select first_package
- source ~/ros702_ws/install/setup.bash
Run the code: ros2 run first_package hello

Node - ROS Logging

In ROS 2, logging is handled by the rcutils logging system.
Include the rclcpp logging header in the source file.
Use the rclcpp logging macros to log messages at different severity levels (DEBUG, INFO, WARN, ERROR, FATAL).

Node - Spinning a Node

Spinning a node keeps it actively running to respond to events and execute callbacks.
This is done using an execution loop, rclcpp::spin().
When Ctrl+C is pressed, ROS gracefully shuts down nodes.
Rclcpp handles signal interrupt (SIGINT).
rclcpp::shutdown() is called automatically during graceful shutdown.

Node - Write a Node with OOP

Complex nodes often require intricate structures and methods.
OOP approach is useful.
Create the class FirstNode in first_package/include/ and implementation in first_package/src/.
Instantiate FirstNode in first_package/src/main.cpp.
- Edit CMakeLists.txt to build.
- Run ros2 run first_package hello.

Turtlebot - Part II

The Turtlebot is a differential wheeled robot.
Movement depends on two separately driven wheels.

Turtlebot - Resources

Read about the origin of the Turtlebot.
Read about the origin of "turtle" in robotics.

Turtlebot - Velocity

Translational velocity (+v for forward, -v for backward).
Angular velocity (+w for counter-clockwise, -w for clockwise rotation).

Turtlebot - Packages

Install packages needed: sudo apt install 'ros-<distro>-turtlebot3*'
Add one of these lines in .bashrc or .zshrc, source it:
- export TURTLEBOT3_MODEL=burger
- export TURTLEBOT3_MODEL=waffle
- export TURTLEBOT3_MODEL=waffle_pi

Turtlebot - Spawn

Spawn the robot in RViz: ros2 launch turtlebot3_fake_node turtlebot3_fake_node.launch.py.
Spawn in Gazebo: ros2 launch turtlebot3_gazebo <launch file>.
Optional: Start RViz. ros2 launch turtlebot3_fake_node rviz2.launch.py.

Turtlebot - Teleoperation

Spawn Turtlebot in RViz.
Move the robot around using keyboard.
- ros2 run turtlebot3_teleop teleop_keyboard.
Visualize messages published on /cmd_vel.
Use ros2 interface show.

Callbacks - Part III

A callback is a function passed to another function.
Used for event handling and asynchronous processing.

Callables

A callable is any entity that can be called with parentheses in C++.

std::function

std::function is a general-purpose polymorphic function wrapper.
It stores callable targets and provides a unified interface.
It uses type erasure to manage different callable types.

Callbacks - Types

Function Pointers
Functions
Lambda functions
Functors/Function Objects

Callbacks - Example

Show an example of function pointer callback.
Show an example for creating a callback using std::function.
Use examples with functors (function objects).

ROS Scheduling - Part IV

Scheduling manages timing and execution of tasks/callbacks within ROS nodes.

ROS Scheduling - `create_wall_timer`

Tool for creating wall timers in ROS 2.
create_wall_timer() function generates a callback at a specified interval based on real-time (wall clock).
Example of using a wall timer to invoke a function at a specified interval.

Exercise #2

Modify first_package to log Hello, world: <n > to the terminal every 500ms.
Increment n with each iteration.

Exercise #3

Modify the previous code to use 500ms instead of a different duration.
Start the counter with a chosen value instead of always starting at 0.

Next Lecture

Lecture 11: ROS (Part 3).
Quiz on ROS.

Appendix A

Examples of higher-order functions from Standard Library.
std::sort
std::find_if and std::find_not
std::remove_if
std::erase_if
std::accumulate
std::all_of, std::any_of, std::none_of
std::for_each

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Description

Test your knowledge on ROS programming as covered in Lecture 10 of the ENPM702 course. This quiz will cover topics such as writing nodes, spinning nodes, and callbacks within the Robot Operating System. Dive into the practical aspects of programming for robotics and assess your understanding of the course material.