PiLiDAR – DIY 360° 3D Panorama Scanner

WORK IN PROGRESS

Core Features:

• LiDAR: custom serial driver for LDRobot LD06, LD19 or STL27L

  • CRC package integrity check
  • Hardware PWM calibrated using curve fitting
  • 2D live visualization and export (numpy or CSV)

• Panorama: 6K 360° spherical map

  • stitched from fisheye photos using Hugin Panorama photo stitcher
  • constant camera exposure by reading EXIF data of automatic
  • constant white balance by iterative optimization of color gains

• 3D Scene: assembly of 3D scenes from 2D planes based on angle and offsets

  • sampling vertex colors from panorama
  • Open3D visualization and export (PCD, PLY or e57)
  • aligning multiple scenes using global registration and ICP fine-tuning
  • Poisson Surface Meshing (very slow on Pi4, recommended to run on PC)

preliminary results

single scans, no registration, no post processing.
klick the images to open the pointclouds in Sketchfab.

Exterior Scan (colormapped Intensity)

Interior Scan (Vertex Colors)

Hardware Specs:

• LDRobot LD06, LD19 or STL27L LiDAR

• Raspberry Pi HQ Camera with ArduCam M12 Lens (M25156H18, p.7)

• Raspberry Pi 4

• NEMA17 42-23 stepper with A4988 driver

• Power Supply:

  • v1: 2x 18650 Batteries (7.2V) with step-down converter
  • v2: 10.000 mAh USB Powerbank with step-up converter

Rev. 1 using 2x 18650 Batteries and Buck Converter

Rev. 2 using 10.000 mAh Powerbank and Boost Converter

stepper driver, motor and gearbox

• A4988 bipolar stepper driver (tutorial)
• NEMA17 42x42x23 bipolar stepper (17HE08-1004S, 17 Ncm torque)
• 3D-printed planetary reduction gearbox (see FDM / 3D printing)

LDRobot LiDAR Specs

angular resolution of LD06 (left) vs. STL27L (right)

LD06:

• sampling frequency: 4500 Hz
• baudrate 230400
• Sales page
• mechanical Datasheet
• Protocol Description

STL27L:

• sampling frequency: 21600 Hz
• baudrate 921600
• datasheet
• wiki
• ROS2 driver git

Scan duration:
12s initialisation
17s shooting 4x photos
1:24m scanning 0.167° x 0.18°
37s stitching, cleanup

wiring

Breadboard Rev. 2

LD06 / STL27L:

• UART Tx (yellow)
• PWM (white)
• GND (black)
• VCC 5V (red)

Raspberry Pi:

• LD06 UART0 Rx: GP15
• LD06 PWM0: GP18
• Power Button: GP03
• Scan Button: GP17
• A4988 direction: GP26, step: GP19
• A4988 microstepping mode: GP5, GP6, GP13

Setup

Power Button (Wakeup & Shutdown)

• Wakeup is hardwired to Pin 3

• enable gpio-shutdown

  > /boot/firmware/config.txt “>

    echo "dtoverlay=gpio-shutdown" >> /boot/firmware/config.txt 
  

• if necesessary:

    sudo nano /etc/systemd/logind.conf
    HandlePowerKey=poweroff
  

enable i2c-GPIO for GY-521 Accelerometer

GY-521 (MPU 6060): Accelerometer, Gyroscope and thermometer
i2c adress: 0x68

Since GPIO3 is hardwired to the Power Button, we need to use i2c-GPIO to map custom i2c pins (tutorial). Unlike serial is not getting crossed, so we connect SDA-SDA and SCL-SCL.
SDA: GPIO22
SCL: GPIO27

disable ic2_arm and enable i2c-gpio in /boot/firmware/config.txt

dtparam=i2c_arm=off
dtoverlay=i2c-gpio,bus=3,i2c_gpio_delay_us=1,i2c_gpio_sda=22,i2c_gpio_scl=27

search for devices on i2c bus 3:

Power LED and CPU fan

# CPU fan at lower temp
echo "dtoverlay=gpio-fan,gpiopin=4,temp=45000" >> /boot/firmware/config.txt


# Power LED Heartbeat:
echo "dtparam=pwr_led_trigger=timer" >> /boot/firmware/config.txt

Scan Button: register GPIO interrupt

make script executable:

chmod +x gpio_interrupt.py

create new service for autostart

sudo nano /etc/systemd/system/pilidar.service

content:

[Unit]
Description=PiLiDAR-Button
After=network.target

[Service]
Type=simple
User=pi
Environment=LG_WD=/tmp
ExecStart=/usr/bin/python3 /home/pi/PiLiDAR/gpio_interrupt.py
Restart=no

[Install]
WantedBy=multi-user.target

reload daemon, enable and start service:

sudo systemctl daemon-reload
sudo systemctl enable pilidar.service
sudo systemctl start pilidar.service

check service if necessary:

sudo systemctl status pilidar.service

set Permission for UART on Raspberry Pi

temporary solution:

sudo chmod a+rw /dev/ttyS0

old solution: make it permanent by disabling password for chmod:

sudo visudo
pi ALL=(ALL:ALL) NOPASSWD: /usr/bin/chmod a+rw /dev/ttyS0

then execute the temporary solution from python:

import subprocess
command = "sudo chmod a+rw /dev/ttyS0"
process = subprocess.Popen(command.split(), stdout=subprocess.PIPE)
output, error = process.communicate()

new solution: grant permissions to the serial port using udev rules

(TODO: check and remove old!)

• forget about visudo and the subprocess call above.
• Open a terminal and run the following command: sudo nano /etc/udev/rules.d/50-ttyS0.rules
• Write the following line in the file and save it: KERNEL=="ttyS0",GROUP="dialout",MODE="0660"
• Run the following command to check if your user is a member of the dialout group: groups
• If you see dialout in the output, you are already a member of the group. If not, run the following command to add your user to the group: sudo usermod -a -G dialout pi
• Run the following command to reload the udev rules: sudo udevadm control --reload-rules
• Unplug and replug the serial device, or reboot the system, to apply the changes.

Hardware PWM on Raspberry Pi

enable GPIO_18 (PWM0) and GPIO_19 (PWM1)

echo "dtoverlay=pwm-2chan" >> /boot/firmware/config.txt 

check if “pwm_bcm2835” now exists:

Install RPi Hardware PWM library:

pip install rpi-hardware-pwm

Panorama Stitching

install Hugin with enblend plugin

sudo apt-get install hugin-tools enblend

power switching the USB port

using uhubctl cli tool. install:

sudo apt-get install uhubctl

list all available hubs and devices

powering Raspberry Pi’s USB-3-Ports (Hub 2) off / on

sudo uhubctl -l 2 -a off
sudo uhubctl -l 2 -a on

jupyter over remote-ssh

start jupyter for network access:

jupyter notebook --ip 192.168.1.16 --no-browser PiLiDAR.ipynb

FDM / 3D printing

3D model files:

• Housing and additional parts (obj and 3mf) in mechanical_design/v2/export.

• M12 to C-Mount lens adapter (thingiverse.com)

• NEMA17 planetary reduction gearbox (printables.com)

Housing CAD model Rev. 2

FDM printing the old front panel (Rev. 1) in PETG

Serial Protocol

LD06

baudrate 230400, data bits 8, no parity, 1 stopbit
sampling frequency 4500 Hz, scan frequency 5-13 Hz, distance 2cm – 12 meter, ambient light 30 kLux

total package size: 48 Byte, big endian.

• starting character：Length 1 Byte, fixed value 0x54, means the beginning of data packet;
• Data Length: Length 1 Byte, the first three digits reserved, the last five digits represent the number of measured points in a packet, currently fixed value 12;
• speed：Length 2 Byte, in degrees per second;
• Start angle: Length: 2 Byte; unit: 0.01 degree;
• Data: Length 36 Byte; containing 12 data points with 3 Byte each: 2 Byte distance (unit: 1 mm), 1 Byte luminance. For white objects within 6m, the typical luminance is around 200.
• End Angle: Length: 2 Byte; unit: 0.01 degree；
• Timestamp: Length 2 Bytes in ms, recount if reaching to MAX 30000；
• CRC check: Length 1 Byte

The Angle value of each data point is obtained by linear interpolation of the starting angle and the ending angle.
The calculation method of the angle is as following:

step = (end_angle – start_angle)/(len – 1)  
angle = start_angle + step*i  

len is the length of the packet, and the i value range is [0, len].

remote Open3D Visualization

using Web Visualizer Plotly to display 3D pointclouds works great in Jupyter.

Plotly seems to render client-sided, unlike Open3D Web Visualizer which renders host-sided and streams jpg sequences, which strains the Pi’s both CPU and WIFI.

Dumping Scans to USB Storage

1. Clone the Repo and run the installer:

   cd /home/pi/PiLiDAR
   git clone https://github.com/LaserBorg/usb_dump --depth 1
   cd usb_dump && chmod +x install.sh && ./install.sh "$(pwd)"
   

2. Create the config file:
   usbdump.json”>

   echo '{"source_directories": ["/home/pi/PiLiDAR/scans"], "target_root_directory": null}' > usbdump.json
   

Troubleshoot USB_dump:

• Check the log file:

• to uninstall the service, run

  chmod +x uninstall.sh && ./uninstall.sh
  

• if the mount point is still persistend after being removed, just delete them.

  Troubleshooting

  Windows Serial Driver

  get CP210x_Universal_Windows_Driver.zip here:
  https://www.waveshare.com/wiki/DTOF_LIDAR_STL27L#Software_Download

  RPi.GPIO RuntimeError: Failed to add edge detection

  current bookworm version has deprecated sysfs GPIO interface removed.
  use LGPIO as described here:

  sudo apt remove python3-rpi.gpio
  sudo apt update
  
  sudo apt install python3-rpi-lgpio
  
  # or in an env without system packages:
  pip3 install rpi-lgpio
  

  LGPIO creates temp-files (issue) like “.lgd-nfy0”. gpio-interrupt.py executes ‘export LG_WD=/tmp’ to set it’s CWD.

  poor performance of VS Code on Raspberry Pi

  disable hardware acceleration for VS Code (source)

  Preferences: Configure Runtime Arguments  
  Set "disable-hardware-acceleration": true
  

  pye57 on Raspberry Pi

  there is no wheel for arm64. build requires libxerces:

  sudo apt install libxerces-c-dev
  pip install pye57
  

  add WIFI via SSH

  tutorial:

  sudo nano /etc/wpa_supplicant/wpa_supplicant.conf
  
  # make sure country code is set:
  country=DE
  

  add entry to wpa_supplicant.conf

  sudo wpa_passphrase "YOUR_SSID" "YOUR_PASSWORD" | sudo tee -a /etc/wpa_supplicant/wpa_supplicant.conf
  

  references:

  inspirations

  • LIDAR_LD06_python_loder and Lidar_LD06_for_Arduino by Inoue Minoru (“henjin0“)
  • ShaunPrice’s StereoPi-supporting fork of BrianBock’s 360-camera script (Article on Medium)

  another Lidar implementation in Python

  • pyLIDAR

  hardware PWM using GPIOZero

  ICP implementations:

  • Aeva Doppler-ICP
  • Photogrammetry & Robotics Bonn KISS-ICP and Lidar-Visualizer

  3D Demo Data for global registration, ICP, meshing etc.:

  • BunnyMesh.ply from 20220201-data
  • DemoICPPointClouds.zip from 20220301-data

  Using a MOSFET for switching: tutorial

  A4988 Enable, Sleep and Reset tutorial