Set up a Lidar Base station for detecting vehicles

This system ultilises a Raspberry Pi 4, Livox Lidar Mid-400, and a screen to create a base station which can help to scan objects.

#lidar   #ros  

Last update: 2022-05-07

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Table of Content

Components

1. Livox Lidar

   Livox Mid-40 provides SDK for Linux native C++ APIs and ROS driver.

   Livox only provides Livox Viewer 0.10.0 for 64-bit Ubuntu 16.04 (Xenial), no source code published.

2. Raspberry Pi 4 B

   • Official Raspberry Pi OS does not have 64-bit version until 20.04 (Bullseye).
   • Ubuntu has provided 64-bit OS version for Raspberry Pi 4 from 18.04 (Bionic).

3. ROS

   Livox ROS driver supports 64-bit Ubuntu 18.04, and ROS Melodic also fully supports Ubuntu 18.04.

Install OS

1. Flash Image

   Download Ubuntu 18.04.5 arm64 raspi3 and use Etcher to flash image to an SD Card.

   After flashing, there are 2 partitions on the SD Card:

   • system-boot: startup files and bootloader configs
   • writeable: root path of system

   By default, Ubuntu image enables the primary mini UART port, and also enables the Linux system console on that port. Connect a USB to TTL serial converter to GPIO 14 (PIN8) and GPIO 15 (PIN 10) to access Pi through the UART port.

   To access Pi through network, follow below instructions. Refer Ubuntu on Raspberry Pi for more information.

2. Configure HDMI LCD (optional)

   This section is for WaveShare 7-inch HDMI LCD.

   In the system-boot partition, add below lines to the end of the file usercfg.txt:

   hdmi_group=2
   hdmi_mode=87
   hdmi_cvt=1024 600 60 6 0 0 0
   dtoverlay=ads7846,cs=1,penirq=25,penirq_pull=2,speed=50000,keep_vref_on=0,swapxy=0,pmax=255,xohms=150,xmin=200,xmax=3900,ymin=200,ymax=3900
   

3. Enable SSH

   Add an empty file ssh in the system-boot partition to enable SSH.

4. Set up Network

   Scan IP in LAN:

   for /L %i in (1,1,254) do ping -n 1 192.168.100.%i | findstr "ms" && echo %i >> ip.txt
   

   Then select an available IP in the network. e.g. 192.168.100.190.

   Starting from Ubuntu 18.04 LTS, Ubuntu uses Netplan to configure network interfaces by default. Edit the Netplan YAML configuration file network-config with the following content:

   version: 2
   ethernets:
   eth0:
       addresses: [192.168.100.190/24]
       gateway4: 192.168.100.1
       nameservers:
           addresses: [192.168.100.4,8.8.8.8]
   wifis:
       wlan0:
           dhcp4: true
           access-points:
               "mynetwork":
                   password: "123456789"
   

   This file is only used once at the first boot

   The configs will be copied to /etc/netplan/50-cloud-init.yaml.

   Scan for IP

   If you don’t want to set a static IP, you can let the router assign an address using dhcp4: true option, and then scan for it later using ARP table.

   Ping all hosts in the LAN:

   for /L %i in (1,1,254) do ping -n 1 192.168.100.%i
   

   Check ARP table, and look for MAC of Pi 3 b8-27-eb or Pi 4 dc-a6-32:

   arp -a | findstr b8-27-eb
   

5. Boot up

   Use SSH to log in with the default user ubuntu, password: ubuntu. Right after the first time logging in, default password have to be changed.

   To skip entering password on sudo command, add current user to sudoers with the rule NOPASSWD:

   sudo bash -c "echo '$USER ALL=(ALL) NOPASSWD: ALL' > /etc/sudoers.d/$USER"
   

6. Install Desktop

   Update packages:

   sudo apt update && \
   sudo apt upgrade -y
   

   Install Unity desktop environment without addons:

   sudo apt install ubuntu-desktop --no-install-recommends
   

   Or install the lightweight Xubuntu desktop without addons:

   sudo apt install xubuntu-desktop --no-install-recommends
   

   Missing packages in a minimal installation

   The option --no-install-recommends will not install many bloat packages (offices, mail, etc.,) that helps to reduce download and install size. However, it may cause GUI does not show up.

   The most happened issue is missing fbdev which shown in the log:

   ~/.local/share/xorg/Xorg.0.log

   ...
   (WW) Warning, couldn't open module fbdev
   (EE) Failed to load module "fbdev" (module does not exist, 0)
   ...
   Fatal server error:
   (EE) no screens found(EE)
   ...
   

   To install fbdev, run:

   sudo apt install xserver-xorg-video-fbdev
   

7. Calibrate touch sensor

   The display can be calibrated via xinput-calibrator.

   sudo apt install xserver-xorg-input-evdev xinput-calibrator
   

   Create calibration config:

   sudo cp -rf /usr/share/X11/xorg.conf.d/10-evdev.conf /usr/share/X11/xorg.conf.d/45-evdev.conf
   sudo nano /usr/share/X11/xorg.conf.d/99-calibration.conf
   

   /usr/share/X11/xorg.conf.d/99-calibration.conf

   Section "InputClass"
       Identifier      "calibration"
       MatchProduct    "ADS7846 Touchscreen"
       Option  "Calibration"   "106 3990 3826 172"
       Option  "SwapAxes"      "1"
       Option "EmulateThirdButton" "1"
       Option "EmulateThirdButtonTimeout" "1000"
       Option "EmulateThirdButtonMoveThreshold" "300"
   EndSection
   

   After reboot, touch will work normally. You can perform touch calibration by clicking the Menu icon on the taskbar, selecting Preferences → Calibrate Touchscreen, and following the displayed prompts.

   Note to save calibration data back to /usr/share/X11/xorg.conf.d/99-calibration.conf.

8. Auto Login

   Add new config for LightDM in

   sudo nano /etc/lightdm/lightdm.conf.d/60-xubuntu.conf
   

   /etc/lightdm/lightdm.conf.d/60-xubuntu.conf

   [Seat:*]
   user-session=xubuntu
   autologin-user=ubuntu
   

9. Automount USB

   Install additional packages:

   sudo apt install thunar-volman gvfs udisks2
   

   Plugged-in USB will be mounted into /media/ubuntu/<Label> or /media/ubuntu/<sdXy>.

Install ROS

Adding repository and source list

sudo apt-add-repository universe
sudo apt-add-repository multiverse
sudo apt-add-repository restricted
sudo apt update

Setup source list to get ROS packages:

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

Add keys:

sudo apt install -y curl && \
curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc | sudo apt-key add -

Pull the package list:

sudo apt update

Install ROS Melodic desktop:

sudo apt install -y ros-melodic-desktop --no-install-recommends

It’s convenient if the ROS environment variables are automatically added to a bash session every time a new shell is launched:

echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc && \
source ~/.bashrc

A good way to check the installation is to ensure that environment variables like ROS_ROOT and ROS_PACKAGE_PATH are set:

printenv | grep ROS

ROS_ETC_DIR=/opt/ros/melodic/etc/ros
ROS_ROOT=/opt/ros/melodic/share/ros
ROS_MASTER_URI=http://localhost:11311
ROS_VERSION=1
ROS_PYTHON_VERSION=2
ROS_PACKAGE_PATH=/opt/ros/melodic/share
ROSLISP_PACKAGE_DIRECTORIES=
ROS_DISTRO=melodic

Initialize the package rosdep to track package dependency:

sudo apt install -y python-rosdep && \
sudo rosdep init && \
rosdep update

Build packages are needed for code compilation.

sudo apt install -y python-rosinstall python-rosinstall-generator python-wstool build-essential

Create a catkin workspace and try to build it:

mkdir -p ~/catkin_ws/src && \
cd ~/catkin_ws/src && \
catkin_init_workspace && \
cd .. && \
catkin_make

The workspace should be built successfully.

Install Livox SDK

Dependency

Livox SDK needs to be built in the host machine, therefore, some tool-chain and build tools have to be installed.

sudo apt update && \
sudo apt install -y build-essential && \
sudo apt install -y curl && \
sudo apt install -y git && \
sudo apt install -y cmake

The Pointcloud Library (PCL):

sudo apt install -y libpcl-dev
sudo apt install -y ros-melodic-pcl-ros

Eigen is a C++ template library for linear algebra:

sudo apt install -y libeigen3-dev

OpenCV (Open Source Computer Vision Library) is an open-source computer vision library:

sudo apt install -y python-opencv python3-opencv

Re-link libraries:

sudo ln -s /usr/bin/vtk6 /usr/bin/vtk

aarch64

sudo ln -s /usr/lib/python2.7/dist-packages/vtk/libvtkRenderingPythonTkWidgets.aarch64-linux-gnu.so /usr/lib/aarch64-linux-gnu/libvtkRenderingPythonTkWidgets.so

Livox SDK

The official guide is at https://github.com/Livox-SDK/Livox-SDK.

Livox SDK is the software development kit designed for all Livox products. It is developed based on C/C++ following Livox SDK Communication Protocol, and provides easy-to-use C style API. With Livox SDK, users can quickly connect to Livox products and receive pointcloud data.

Installation

git clone https://github.com/Livox-SDK/Livox-SDK.git && \
cd Livox-SDK && \
cd build && \
cmake .. && \
make && \
sudo make install

The Livox SDK will be built and installed in /usr/local/lib:

Install the project...
-- Install configuration: ""
-- Installing: /usr/local/lib/liblivox_sdk_static.a
-- Installing: /usr/local/include/livox_def.h
-- Installing: /usr/local/include/livox_sdk.h

Install Livox ROS Driver

Get livox_ros_driver from GitHub

git clone https://github.com/Livox-SDK/livox_ros_driver.git ws_livox/src

Then build it:

cd ws_livox && \
catkin_make

Compilation errors

• If running catkin_make gives error of command not found, it’s probably that the ROS setup.bash is not executed and included in ~/.bashrc. See above section to source it.

• If gcc is halted, usually it is caused by lack of memory. The compilation takes more than 1.2 GB of RAM at peak!

Test Lidar

1. Chang Ethernet IP to static IP in subnet 192.168.1.0/24:

   /etc/netplan/50-cloud-init.yaml

   version: 2
   ethernets:
   eth0:
       addresses: [192.168.1.12/24]
       gateway4: 192.168.1.1
   

2. Use Livox Viewer to set a Static IP for the Lidar module. Livox only accepts IP in 192.168.1.0 subnet.

3. Then run the livox_lidar_rviz example:

   cd ws_livox
   source ./devel/setup.bash
   roslaunch livox_ros_driver livox_lidar_rviz.launch
   

   This will run Livox ROS and Rviz to visualize the received pointcloud.

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