In this tutorial, we will explore the basics of ROS Noetic Ninjemys (ROS Noetic), the latest distribution of ROS.

ROS has a steep learning curve. I remember when I first started learning ROS, my head was spinning. There was all this new vocabulary you have to learn: nodes, packages, subscribers, publishers, etc. It was like learning some obscure foreign language for the first time.

To get the most out of ROS, I recommend going through Part 1 and Part 2 of this tutorial. My advice to you is to not worry if everything seems complicated and doesn’t make sense. Don’t worry if you can’t understand how any of these abstract concepts connect to a real-world robot. 

ROS is built in such a way that you need to work through the boring basics before you can use it to develop actual robotics projects. You have to walk before you learn how to run.

After you work through the basics of ROS, you’ll start applying those basics to actual robotics applications using ROS. It’s at that point that all that abstract stuff that you will learn below will come together and finally make sense. 

If you start to build robots with ROS without learning the basics of ROS, you’ll get super confused. It would be like trying to go to a foreign country and trying to speak their language without ever having learned basic words and phrases.

ROS doesn’t allow you to skip steps in the learning process. You have to build your knowledge of the basics of ROS, brick by boring brick, in order to use it to build fun robots that solve real-world problems.

So be patient in the learning process, and I assure you that you’ll master ROS and will be building cool robots in no time.

Without further ado, let’s get started!

Prerequisites

• You have installed ROS Noetic.
• You understand how to create a simple “Hello World” program in C++.
• You understand the basics of Python.
• You understand the basics of Linux.

ROS Noetic Ninjemys Tutorial – Part 1 of 2

• How to Find the Path of a Package
• How to List the Files Inside a Package
• How to List All Installed Packages
• How to Get a List of All Publicly Available ROS Packages
• How to Change Your Current Working Directory
• How to Create a New Package
• How to Build a Package
• Common ROS Package Commands
• How to Create a Publisher Node
• How to Create a Subscriber Node
• How to Build a Node
• How to Run a Node
• How to Create Custom Messages
• How to Publish and Subscribe to Custom Messages
• How to Create a Service
• How to Create a Launch File

When you’ve finished the tutorials above, go on to Part 2.

In this post, we will install ROS Noetic Ninjemys. As of the date of this tutorial, ROS Noetic Ninjemys is the latest ROS distribution that has long term support. It will be supported until May 2025.

You Will Need

In order to complete this tutorial, you will need:

• Ubuntu 20.04 installed and running properly  (I’m running my Ubuntu in a VirtualBox on Windows 10)

Directions

The official steps for installing ROS are at this link at ROS.org, but I will walk you through the process below so that you can see what each step should look like.

Select Noetic Ninjemys on this page.

Next, select your platform. I am using Ubuntu, so I will click on the Ubuntu option.

Now we need to configure our repositories to allow “restricted”, “universe,” and “multiverse.

Click the 9 white dots at the bottom left of your screen.

Search for Software & Updates. Then click on it.

Make sure main, universe, restricted, and multiverse are all checked. Then click Close.

Now open up a new terminal window, and type (or copy and paste) the following command:

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'

The command above sets your computer up to accept software from packages.ros.org. 

Now we need to set up the secure keys so that our system accepts what we are going to download. 

Type or copy & paste the following command.

sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654

Now, update the package list. This command makes sure you have the most recent list of software packages that can be installed in your Linux system.

sudo apt update

Now do a full desktop install of ROS. The command below installs all the software, tools, algorithms, and robot simulators for ROS.

sudo apt install ros-noetic-desktop-full

After you type the command and press Enter, press Y and hit Enter when asked if you want to continue. It will take a while to download all this stuff, so feel free to take a break while ROS downloads to your system.

Set up the environment variables. These variables are necessary in order for ROS to work.

Type the following commands, one right after the other. We are using Bash, so this is what we type:

echo "source /opt/ros/noetic/setup.bash" >> ~/.bashrc

source ~/.bashrc

Check that the environment variables are properly set up. Type the following command:

printenv | grep ROS

Here is what you should see:

Let’s also check our .bashrc file to see if the “source /opt/ros/noetic/setup.bash” line was added to it successfully.

gedit .bashrc

There it is at the bottom of the .bashrc file.

Now, let’s create a ROS workspace.

A workspace is a folder that contains other folders that store related pieces of ROS code.

The official name for workspaces in ROS is catkin workspaces. The word ‘catkin’ comes from the tail-shaped flower cluster found on willow trees (see photo below) — a reference to Willow Garage, the original developers of ROS. 

All the ROS software packages that you create need to reside inside a catkin workspace. The name of this catkin workspace can be anything, but by convention, it is typically called catkin_ws.

Open a new terminal window, and type the following commands, one right after the other.

First create the workspace.

mkdir -p ~/catkin_ws/src

Move inside the workspace.

cd ~/catkin_ws/

Build the workspace.

catkin_make

You should now have a build, devel, and src folder. Type this command to see those:

dir

Now, source the new setup.*sh file. This is a file that makes sure your workspace is recognized in your ROS environment.

source devel/setup.bash

Let’s add this code to the .bashrc file so that we don’t have to run it everytime we open a new terminal window.

echo "source ~/catkin_ws/devel/setup.bash" >> ~/.bashrc

We can check to see if that was set up properly by typing this command:

echo $ROS_PACKAGE_PATH

Finally, let’s launch a program to do a final check everything is set up properly. We will launch a simulation of a turtle.

Open a new terminal window, and type this command:

roscore

Open a new terminal tab, and type this command:

rosrun turtlesim turtlesim_node

Here is what you should see:

Congratulations. You have installed ROS!

From here, you can go check out the basics of ROS Noetic Ninjemys. If you’re already familar with ROS, it is often helpful to go through these tutorials to refresh the basics.

Keep building!

In this tutorial, we’ll learn how to create a ROS package. Software in ROS is organized into packages. Each package might contain a mixture of code (e.g. ROS nodes), data, libraries, images, documentation, etc. Every program you write in ROS will need to be inside a package.

ROS packages promote software reuse. The goal of a ROS package is to be large enough to provide a specific useful functionality, but not so large and complicated that nobody wants to reuse it for their own project.

ROS packages are organized as follows:

• launch folder: Contains launch files
• src folder: Contains the source code (C++, Python)
• CMakeLists.txt: List of cmake rules for compilation
• package.xml: Package information and dependencies

Here is the official ROS tutorial on how to create a ROS package. I will walk you through this process below.

Directions

Here is the syntax for creating a ROS package. Do not run this piece of code.

catkin_create_pkg <package_name> [depend1] [depend2] [depend3]

package_name is the name of the package you want to make, and depend1, depend2, depend3, etc., are the names of other ROS packages that your package depends on.

Now, open a new terminal window, and move to the source directory of the workspace you created. If you don’t already have a workspace set up, check out this tutorial.

cd ~/catkin_ws/src

Create a ROS package named ‘hello_world’ inside the src folder of the catkin workspace (i.e. catkin_ws). This package will have three dependencies (i.e. libraries the package depends on in order for the code inside the package to run properly): roscpp (the ROS library for C++), rospy (the ROS library for Python), and std_msgs (common data types that have been predefined in ROS … “standard messages”).

catkin_create_pkg hello_world std_msgs rospy roscpp

Type dir , and you will see that we now have a package named hello_world inside the source folder of the workspace. 

Change to the hello_world package.

cd hello_world

Note, we could have also used the ROS command to move to the package.

roscd hello_world

Type:

dir

You can see that we have four files:

CMakeLists.txt: This text file contains the commands to compile the programs that you write in ROS. It also has the commands to convert your source code and other files into an executable (i.e. the code that your computer can run).

include: Contains package header files. You might remember when we wrote header files in the C++ tutorial…well this folder is where your header files would be stored.

src: This folder will contain the C++ source code. If you are doing a project in Python, you can create a new folder named scripts that will contain Python code. To create this new folder type:

mkdir scripts

package.xml: This is an Extensible Markup Language (XML) file. An XML file is a text file written in a language (called XML) that is easy to read by both humans and computers. An XML file does not do anything other than store information in a structured way. 

Our package.xml file contains information about the hello_world package. You can see what is inside it by typing:

gedit package.xml

That’s it! You’re all done.

Note that if you ever want to go straight to a package without typing the full path, ROS has a command to enable you to do that. In the terminal window, type the following:

 roscd <package_name>

For example, if we want to go straight to the hello_world package, we would open a new terminal window and type the following command:

roscd hello_world

Compiling a Package in ROS

When you create a new package in ROS, you need to compile it in order for it to be able to run. The command to compile a package in ROS is as follows:

catkin_make

The command above will compile all the stuff inside the src folder of the package.

You must be inside your catkin_ws directory in order for the catkin_make command to work. If you are outside the catkin_ws directory, catkin_make won’t work.

To get to your catkin_ws directory, you can type this command anywhere inside your terminal:

roscd

cd ..

Then to compile all the packages inside the catkin workspace, you type:

catkin_make

If you just want to compile specific packages (in cases where your project is really big), you type this command:

catkin_make --only-pkg-with-deps

For example, if you have a package named hello_world, you can compile just that package:

catkin_make --only-pkg-with-deps hello_world