LiDAR: How autonomous-driving car sees

Vehicle autonomy and driving assistance rely on many technologies. One of them is LiDAR (Light Detection And Ranging). LiDAR is key technology in an autonomous driving car nevertheless it is not the only one in car which keeps you on a road safe and sound.

LiDAR sensors measure the distance to an object by calculating the time taken by a pulse of light to travel to an object and back to the sensor. This simple equation shows what is needs to be calculated for every single beam from transmitter to receiver.

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The 3D LiDAR take place on the top of a car because it can provide 360° 3D view of obstacles that vehicle must avoid or take notice of being there. 3D LiDAR use 905 nm wavelength that can give us sight for almost 100 m range in field-of-view. Some companies are building 3D LiDAR with wavelength of 1550 nm to provide longer range and much higher accuracy.

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3D LiDAR view

Using LiDARs need some special requirements like remove sensitivity to ambient light and to prevent spoofing from other LiDARs. Next one and really important is that it sends a beam and that can be dangerous for our eyes so every single transmitter has to be “eye-safe”. Lately companies have been using 3D LiDARs which are physically spin around and they get 360° field-of-view. These sensors are expensive so the trend is Solid State 3D LiDARs due to their long-term reliability, price and size. SSLs currently have lower field-of-view coverage but they are much cheaper. It is possible to place multiple sensors on car to cover a larger area and still spend less money than using spinning 3D LiDARs.

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Solid State LiDAR mounted in front of the car and its view

There are some disadvantages and weaknesses of using 3D LiDAR. They are large and expensive and must be mounted outside on the roof of the vehicle. That will not give us information about close objects near the vehicle. The system which Google is using weight 80 kg and costs $70,000.

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Combination of 3 SSLs with object and sign recognition

 

 

There is also the happy medium what is multi beam 2D LiDAR. They are giving us just 2D scans of the surrounding world (with one or few beams i.e. scan planes) and often in smaller (like 180°) field of view. Most likely these LiDARs contains 4 – 6 beams transmitters to be precise as possible. They are much cheaper and more start-up companies are using them to subsite classic 3D LiDAR.

 

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Rotating 3D LiDAR on the UBER car

LiDAR works well in all light condition but when it starts to rain, snow or when the air is filled with dust. Due to use of light spectrum of wavelength no beams are reflected from actual road or objects around. It will lose a vison and can fail the self-driving. Snow is a big issue for autonomous cars because beams are absorbed in it. The company that will be able to drive a car in these conditions will be successful on the self-driving cars

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Google car 3D LiDAR data with object recognition

market. LiDAR cannot detect colour or contrast and cannot provide optical character recognition capabilities. We will need some information to drive. For example, about color of signs etc. We will need to add one more system in a car. On the other side, LiDAR is one of the most reliable and simple to use system to keeps us on track and recognize people and objects to avoid them when driving.

In conclusion, here is table with different types of LiDARs + prices and links.

Type of LiDAR Average Price Links
3D LiDAR $70,000 https://goo.gl/25AuRH
2D LiDAR $2000 – $4000 https://goo.gl/MVgBiS
Solid State LiDAR $100 – $300 https://goo.gl/yvqciL

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