Description

LiDAR integration with ROS Noetic and Ubuntu on Raspberry Pi

Story

As you already know, ROS Noetic is mainly developed for Ubuntu 20.04, so Ubuntu is the recommended Linux OS for installation. This tutorial explains how to install ROS Noetic on the Raspberry Pi and how to connect your LiDAR to Raspberry Pi 4 Model B using ROS Noetic middleware on Ubuntu Server 20.04.

Prerequisites

Before you get started with this tutorial, you will need the following:

Raspberry Pi 4 Model B
RPLidar A1M8
A computer with an internet connection and the ability to flash your microSD card. Here we’ll be using laptop.
High-performance microSD card: 32GB minimum
MicroSD to SD adapter
You will need a monitor, keyboard, and mouse (at least for the initial setup)
ROS applications use a lot of compute resources and the heat sink may not be enough for the heat generated. Consider adding a cooling fan to your Raspberry Pi 4.
Some experience with ROS is helpful but not required.

So, let's get started.

Step 1: Download the Ubuntu Server image and flash it

First you have to download the OS image. Go to the download page of the Ubuntu official website.

Download and install Etcher from the website.
Click Select Image in Etcher.
Attach your SD card to the computer. Etcher will select it automatically.
Click Flash! to write the image file to the SD card.

When done, remove the SD card, insert it into your Raspberry Pi.

Step 2: Boot your Raspberry Pi

You probably already know that you need a few things to get started with Raspberry Pi such as a mouse, keyboard, HDMI cable etc.

Plug in a mouse and a keyboard.
Connect the HDMI cable.
Insert your MicroSD card.
Plug in your Ethernet cable, if you’re using one.

When everything else is set up, power it on your Raspberry Pi by plugging the power cable. After powering on your Raspberry Pi, wait for the boot process to complete and you should see the following message on window.

login: ubuntu
password: ubuntu

The first time you log in, you’ll be asked to change this password.

After changing the default password, you should be greeted by a message confirming that you’re now connected.

Step 3: WiFi setup using netplan

Starting from Ubuntu 18.04 LTS, Ubuntu uses Netplan to configure network interfaces by default. Netplan is a utility for configuring network interfaces on Linux. Netplan uses YAML files for configuring network interfaces. YAML configuration file format is really simple. It has clear and easy to understand syntax.

To be able to setup Wifi on Raspberry Pi, you first need to get the name of the wifi card by showing physical components using the following command:

sudo lshw

In my case it was wlan0. Then navigate to /etc/netplan/ using the cd command

cd /etc/netplan/

Edit the Netplan YAML configuration file /etc/netplan/50-cloud-init.yaml with the following command:

sudo nano 50-cloud-init.yaml

Add your WiFi access information. Make sure not to use tab for space, use the spacebar to create the blank.

# This file is generated from information provided by
# the datasource.  Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    version: 2
    ethernets:
        eth0:
            optional: true
            dhcp4: true
    # add wifi setup information here ...
    wifis:
        wlan0:
            optional: true
            access-points:
                "YOUR-SSID-NAME":
                    password: "YOUR-NETWORK-PASSWORD"
            dhcp4: true

Change the SSID-NAME and the YOUR-NETWORK-PASSWORD with your information. Close and save the file using ctrl+x and press yes.

Now, check whether there’s any error in the configuration file with the following command:

sudo netplan –debug try

If any error encounters then you can check with this command for detailed error information.

sudo netplan --debug generate

Apply the configuration file with the following command:

sudo netplan --debug apply

Finally, reboot your PI

sudo reboot

Step 4: Updating and upgrading software packages on your Pi

To make sure all dependencies are up to date, run the following command

sudo apt-get update

If you want to get the latest versions of software you installed already, run

sudo apt-get upgrade

This command upgrades all the software on your Pi to the latest version. It can take a while to run, so you don’t need to do it often. You have to press Y and Enter to confirm.

Step 5: Enabling SSH

Get the current status of the ssh server.

sudo systemctl ssh status

If you see errors, then the ssh rsa key is invalid and you would have to regenerate the keys.

sudo ssh-keygen -A

then run:

sudo systemctl start ssh

Check the status again.

If ssh is active on your raspberry, you can log on to the target device from your computer via a terminal.

Step 6: SSH into your Raspberry Pi

Now that you have enabled SSH and found out your IP address you can go ahead and SSH into your Raspberry Pi from any other computer. You’ll also need the username and the password for the Raspberry Pi.

Default Username and Password is:

username: ubuntu
password: your_password

Open a terminal (on Mac and Linux) on the computer from which you want to SSH into your Pi and type the command below. On Windows, you can use a SSH client like Putty.

Linux and macOS user have an SSH client installed by default, and can SSH into the Pi by typing:

ssh ubuntu@pi_ip_address

When you connect through SSH for the first time, you will be prompted to accept the RSA key fingerprint, Type “yes” to continue. You have learned how to enable SSH on Raspberry Pi.

Step 7: Add Swap Space(optional)

This step is not mandatory, however if you have either Raspberry Pi 4 Model B with RAM 2GB or 4GB proceed by running below commands to add additional swap memory.

You can verify that there is no active swap using the free utility:

free -h

Output:

total   used   free   shared buff/cache  available
Mem:  3.7Gi  206Mi   2.5Gi   3.0Mi   1.1Gi       3.4Gi
Swap: 0B     0B     0B

We will use the fallocate program to create a swap file.

sudo fallocate -l 2G /swapfile

Now check if the file was created.

ls -lh /swapfile

If it was created correctly, you should see something like:

-rw-r--r-- 1 root root 2.0G Oct 26 19:05 /swapfile

Make the file only accessible to root by typing:

sudo chmod 600 /swapfile

Verify the permissions change by typing:

ls -lh /swapfile

Output:

-rw------- 1 root root 2.0G Oct 26 19:05 /swapfile

As you can see, only the root user has the read and write flags enabled.

We can now mark the file as swap space by typing:

sudo mkswap /swapfile

If it was successful, you should see something like

Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=f9dfa448-79af-4dc5-a49c-892fd73ca3ba

Finally we will tell the system to start using our new swap file,

sudo swapon /swapfile

To verify that the swap is now available type:

sudo swapon --show

Result:

NAME TYPE SIZE USED PRIO
/swapfile file  2G  0B  -2

This swap will only last until next reboot. In order to make it permanent, we will add it to the /etc/fstab file.

echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Reboot you Raspberry PI.

After reboot, verify it using free -h command.

total  used   free    shared buff/cache  available
Mem:    3.7Gi  191Mi  3.2Gi  3.0Mi  307Mi        3.5Gi
Swap:   2.0Gi  0B    2.0Gi

Step 8: Enable X11 forwarding

X11 Forwarding allows us to run software on Linux/Unix server with a Windows style GUI (Graphical User Interface). When you run a SSH, TELNET or RLOGIN/RSH session you will be able to display your remote applications directly on your local Windows PC or Mac Os.

For Mac, use XQuartz. You can install XQuartz using homebrew with brew cask install xquartz or directly from the website here
For Windows, use PuTTY and VcXsrv.

Open up a terminal window and launch XQuartz.

open -a XQuartz

Allow connections from remote clients

xQuartz’s Preference → Security → Allow connections from network clients

You can also execute the following command to disable the access control, by which you can allow clients to connect from any host. Open up a terminal window and run the following at the command line:

xhost +

You should see a response like this:

access control disabled, clients can connect from any host

You will see XQuartz server in the Dock. Leave this terminal window runningwithout closing.

Open up a second terminal and run the following command in order to connect to your Raspberry Pi, remember to use the -X flag to enable X11 window forwarding:

ssh username@hostname -X

You should let your Raspberry Pi forward x11 display. Update /etc/ssh/sshd_config and set X11 Forwarding yes, then restart your Raspberry PI server.

Then, install x11-apps:

sudo apt install x11-apps

Test X11 by running xeyes or xclock or any another GUI application you wish. The syntax is as follows on your remote server:

xeyes

If you still get the “cannot open display” error, set the DISPLAY variable as shown below.

export DISPLAY='<ip_address_of_your_PC>:0.0'

IP is the local workstation’s IP where you want the GUI application to be displayed.

Run again:

xeyes

If everything is correct, we will get the following screen:

Now you can configure and login using X-servers to X Forward.

Step 9: Setup your sources.list

Setup your raspberry pi to accept software from packages.ros.org.

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

If the command succeeds, you won’t see any output message.

Step 10: Set up your keys

By running the following command, we will download the key from Ubuntu’s keyserver into the trusted set of keys:

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

Output:

Executing: /tmp/apt-key-gpghome.DFEscOhTF9/gpg.1.sh --keyserver hkp://keyserver.ubuntu.com:80 --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654
gpg: key F42ED6FBAB17C654: "Open Robotics <info@osrfoundation.org>" not changed
gpg: Total number processed: 1
gpg: unchanged: 1

Step 11: Installation of ROS

First, make sure your Debian package index is up-to-date:

sudo apt update

Now pick how much of ROS you would like to install.

Desktop-Full Install: : Everything in Desktop plus 2D/3D simulators and 2D/3D perception packages
Desktop Install: Everything in ROS-Base plus tools like rqt and rviz
ROS-Base: (Bare Bones) ROS packaging, build, and communication libraries. No GUI tools.

I’ll go with installing Desktop Install here.

sudo apt install ros-noetic-desktop

It takes around 1 hour for downloading and installation processes.

Finally run,

sudo apt-get install build-essential

Step 12: Verify Noetic installation on your Raspberry Pi 4

Let’s try some ROS commands to make sure the installation has finished successfully. A simple way to check the functionality of ROS is to use the turtlesim simulator that is part of the ROS installation.

Open up a terminal window and run the following at the command line:

xhost +

Leave this terminal window running.

Open a new terminal, connect to your Raspberry Pi via ssh and run the following commands:

You must source in every bash terminal you use ROS.

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

Then run,

roscore

Leave this terminal window running as well.

Because roscore is running in the foreground, you need to open up another terminal window to connect via ssh using ssh username@hostname -X to your Raspberry Pi

Source it again. Then run:

export DISPLAY='<ip_address_of_your_PC>:0.0'

and finally run the simulation command.

rosrun turtlesim turtlesim_node

If everything is correct, we will get the following screen:

Open up yet another terminal window. Run the following:

rosrun turtlesim turtle_teleop_key

Click the mouse in the last container window you created so that it has focus. Use the arrow keys to move the turtle around the screen.
If everything goes right, you will obtain the following result on current terminal:

Press Ctrl-C to stop roscore, etc.

Congratulations! We are done with the ROS installation.

Step 13: Connect your RPLiDAR to Raspberry Pi

Connect your RPLiDAR to Raspberry Pi 4 Model B using Micro USB Cable. Flashing green light indicates normal activity of sensor.

Once you have connected the RPLiDAR to your Raspberry Pi, type the following command line to check the permissions:

Open your terminal and run the following command.

ls -l /dev | grep ttyUSB

Output of the following command must be:

crw-rw----  1 root   dialout 188,   0 Jan  3 14:59 ttyUSB

Run below command to change permission:

sudo chmod 666 /dev/ttyUSB0

Once the permissions are configured, you have to download and install the RPLIDAR ROS packages.

Step 14: Install RPLIDAR ROS Package

Let’s create a separate workspace for other packages, that are not part of core ROS.

Create the catkin root and source folders:

mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/

Configure the catkin workspace

catkin_init_workspace

and source it to bashrc:

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

Okay, we’re ready to start installing RPLIDAR ROS package. Go to the source folder of the catkin workspace that you just created:

cd src

Clone the ROS node for the Lidar in the catkin workspace.

sudo git clone  https://github.com/Slamtec/rplidar_ros.git

After that build with catkin.

cd ~/catkin_ws/

Run catkin_make to compile your catkin workspace.

catkin_make

Then run to source the environment with your current terminal. Don't close the terminal.

source devel/setup.bash

and launch RPILIDAR launch file

roslaunch rplidar_ros rplidar.launch

If you can see scan messages on terminal windows, everything works as it supposed to work.

Step 15: Data display with Rviz using X11 forwarding

RVIZ is a ROS graphical interface that allows you to visualize a lot of information, using plugins for many kinds of available topics.

Open a terminal, connect to your Raspberry Pi via ssh and run the following commands:

source /opt/ros/noetic/setup.bash

Then run roscore:

roscore

Open a new terminal, connect to your Raspberry Pi via ssh and run the following commands:

cd ~/catkin_ws/

Then run to source the environment with your current terminal.

source devel/setup.bash

Then we launch the Rplidar launch file in the package.

roslaunch rplidar_ros rplidar.launch

Finally open last terminal window and connect to your Raspberry Pi via ssh using ssh username@hostname -X command

Source it:

source /opt/ros/noetic/setup.bash

Then run,

export DISPLAY='<ip_address_of_your_PC>:0.0'

And finally run

rviz

You will obtain the following result on current terminal:

[ERROR] [1604066165.661029569]: Unable to create the rendering window after 100 tries.
[ INFO] [1604066165.661137306]: Stereo is NOT SUPPORTED
terminate called after throwing an instance of 'std::logic_error'
  what():  basic_string::_M_construct null not valid
Aborted (core dumped)

The X protocol is based on remote procedure calls to the X server. Unfortunately, this doesn't really work for OpenGL calls so you cannot run programs that require 3D acceleration using X forwarding.

You can check running glxgears command. It is a test program to make sure your graphics accelerations are working. You can try glxgears as well to prove your OpenGL rendering hardware/software pipeline is working.

glxgears

If glxgears doesn't work then rviz probably won't either. Rviz needs OpenGL which doesn't work via X forwarding.

Have a look to VirtualGL as alternative. VirtualGL is an open source toolkit that gives any Unix or Linux remote display software the ability to run OpenGL applications with full 3D hardware acceleration. Normal X-forwarding sends all X rendering instructions and the client does all the rendering on a CPU. VirtualGL overrides this protocol and renders 3D graphics at the host’s GPU and then send only the rendered 2D images to the client.

So, we are going to install minimal ubuntu desktop on raspberry pi and run rviz locally.

Step 16: Install the desktop components and VNC server

Once you've installed Ubuntu Server you will need a mechanism to be able to launch GUI application. As a result many people actually install Ubuntu Desktop instead of installing Ubuntu Server since the desktop version of Ubuntu has the GUI built in. There is a better way however, and that is to install VNC. VNC provides a virtual desktop so it is more lightweight than a full blown desktop installation.

Virtual Network Computing (VNC) allows you to use GUI applications over a remote connection. Virtual Network Computing is a lot like X11 forwarding on steroids. For the server, the easiest for Ubuntu would be X11VNC. It is very simple to install and to use. This program is not only free of charge, open source, but also supports OpenGL programs. For example, rviz and other programs can also open normally.

There are plenty of desktop flavours but Xfce is perhaps one of the lighter and more popular flavours so we will go for that one. Xfce is a lightweight desktop environment for UNIX-like operating systems. It aims to be fast and low on system resources, while still being visually appealing and user friendly.

So type the following command:

sudo apt-get install xfce4-goodies xfce4

when prompted type Y and then press [Enter]. This will install the basic xfce desktop components. We have three display managers – LightDM, GDM and SDDMC. Choose the display manager over to lightdm.

Then reboot your raspberry Pi.

sudo reboot

Connect to your raspberry PI and open a terminal and issue the following

cat /etc/X11/default-display-manager

This will return :

/usr/sbin/lightdm

Open a terminal and run the following commands to update default repositories and install required packages.

sudo apt-get install x11vnc -y

Now create a password to connect using vnc viewer from the client system. This will not require any username to connect vnc.

x11vnc -storepasswd /etc/x11vnc.pwd

After the successful installation of the x11vnc server on your system. Let’s start it using the following command. Change the parameters as per your setup.

sudo x11vnc -auth guess -capslock -forever -loop -noxdamage -repeat -rfbauth /etc/x11vnc.pass -rfbport 5900 -shared

The VNC server will start on default port 5900.

To connect to the server using VNC, you need a VNC client on your system. VNC viewer clients are available for Windows, Linux and Macintosh workstations.

For this tutorial, I am using RealVNC viewer on our system. You can use any other client of your choice.

Start your VNC viewer and open a new connection using ip address of your Raspberry Pi.

Your VNC desktop session appears. Now you have connected to Ubuntu Server, and you can use graphical user interface to work with it.

You can successfully configured VNC server on your Ubuntu system.

Step 17: Running rviz with VNC on a remote computer

We assume that you've already done the installation step.

Open a terminal windows and run the following command:

source /opt/ros/noetic/setup.bash

Then run roscore:

roscore

Without roscore running, the various nodes within ROS can’t talk to each other. So you need to leave it running in the background.

Open a new terminal and run the following commands:

cd ~/catkin_ws/

Then run to source the environment with your current terminal.

source devel/setup.bash

and launch RPILIDAR launch file

roslaunch rplidar_ros rplidar.launch

To check if the node we just launched really publishing something, we open another terminal windown and type:

rostopic echo -n1 /scan

If everything goes right, you will obtain the following result on current terminal:

header:
seq: 5032
stamp:
secs: 1604073153
nsecs: 896877623
frame_id: "laser"
angle_min: -3.1241390705108643
angle_max: 3.1415927410125732
angle_increment: 0.01745329238474369
time_increment: 0.00037511246046051383
scan_time: 0.1346653699874878
range_min: 0.15000000596046448
range_max: 12.0
ranges: [0.32100000977516174, 0.32100000977516174, 0.3240000009536743, 0.3269999921321869, 0.33000001311302185, 0.3319999873638153, 0.3330000042915344, 0.3370000123977661, 0.33899998664855957, 0.34299999475479126, 0.3449999988079071, 0.34700000286102295, 0.35199999809265137, 0.3540000021457672, 0.3580000102519989, 0.3630000054836273, 0.36899998784065247, 0.3709999918937683, 0.37700000405311584, 0.38100001215934753, 0.3889999985694885, 0.3919999897480011, 0.3959999978542328, inf, 0.2160000056028366, 0.2160000056028366, inf, inf, inf, 5.068999767303467, inf, inf, inf, inf, inf, 4.505000114440918, 4.375, 4.3429999351501465, 4.244999885559082, inf, inf, 0.33399999141693115, 0.32600000500679016, 0.3190000057220459, 0.3149999976158142, 0.3059999942779541, 0.3019999861717224, 0.3009999990463257, 0.29899999499320984, 0.3019999861717224, 0.31200000643730164, 0.33000001311302185, inf, inf, inf, inf, 3.38700008392334, 3.367000102996826, 3.3239998817443848, 3.308000087738037, 3.2699999809265137, 3.256999969482422, 3.239000082015991, 3.2339999675750732, 3.2090001106262207, 3.196000099182129, 3.1689999103546143, 3.1579999923706055, 3.1429998874664307, 3.132999897003174, 3.11899995803833, 3.115000009536743, 3.1080000400543213, 3.0829999446868896, 3.0880000591278076, 3.0799999237060547, 3.072000026702881, 3.049999952316284, 3.0480000972747803, 3.0429999828338623, 3.0460000038146973, 3.0409998893737793, 3.0420000553131104, 3.0429999828338623, 3.0360000133514404, 2.51200008392334, 2.1019999980926514, 1.9160000085830688, 1.593999981880188, 1.3669999837875366, 1.2120000123977661, 1.1540000438690186, 1.0420000553131104, 0.949999988079071, 0.9120000004768372, 0.8379999995231628, 0.7710000276565552, 0.7160000205039978, 0.6899999976158142, 0.6449999809265137, 0.6079999804496765, 0.5899999737739563, 0.5609999895095825, 0.5360000133514404, 0.5109999775886536, 0.5, 0.47999998927116394, 0.460999995470047, 0.4519999921321869, 0.4339999854564667, 0.4180000126361847, 0.41100001335144043, 0.38999998569488525, 0.382999986410141, 0.3700000047683716, 0.35899999737739563, 0.3529999852180481, 0.3440000116825104, 0.33799999952316284, 0.32899999618530273, 0.3199999928474426, 0.3160000145435333, inf, 0.3050000071525574, 0.2939999997615814, 0.29100000858306885, inf, 0.27799999713897705, 0.27000001072883606, 0.27300000190734863, 0.26600000262260437, 0.257999986410141, 0.25600001215934753, 0.2540000081062317, 0.25, 0.24799999594688416, 0.23999999463558197, 0.24400000274181366, 0.23899999260902405, 0.2370000034570694, 0.23000000417232513, 0.2329999953508377, 0.2280000001192093, 0.2240000069141388, 0.22300000488758087, 0.22100000083446503, inf, 0.2199999988079071, 0.2150000035762787, 0.21400000154972076, 0.21199999749660492, 0.21299999952316284, 0.20999999344348907, 0.20900000631809235, 0.20800000429153442, 0.2070000022649765, 0.20600000023841858, 0.20499999821186066, 0.20399999618530273, 0.20200000703334808, 0.2029999941587448, 0.20100000500679016, 0.20000000298023224, 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---

Let’s check it further with Rviz by typing.

rviz

You'll see the rviz window pops out.

The visualization is not showing due to some problems with the frame.

We now need to tell rviz which fixed frame we want to use. Change fixed frame to laser.

Now add a LaserScan using Add button.

Now everything looks fine.

Rviz will open with a map of the RPLIDAR’s surroundings.

The view from the laser scanner will be marked in red. The laser scanner is positioned at the center of the grid, it has a range of roughly 15cm to 6 meters, so you’ll be able to see everything around it on its scanning plane within that range.

That’s it for today! You have ROS Noetic installed and ready to use!

I hope you found this guide useful and thanks for reading. If you have any questions or feedback? Leave a comment below. Stay tuned!