New energy vehicle manufacturing has experienced rapid development in the past two years.
 

Domestic companies such as NIO, Ideal, and Xiaopeng have all raised a large amount of funds in the capital market. Early new energy vehicles started with new energy electric vehicles because the threshold for autonomous driving was high. However, with the development of technology and the needs of customer trends, autonomous driving has to be put on the agenda. Although Tesla's Musk disdains LiDAR, most manufacturers except Tesla are still using LiDAR as the main sensor. Therefore, LiDAR is an unavoidable obstacle in autonomous driving, and this article provides a detailed explanation of the parameters of LiDAR. i82ednc


The role of LiDAR in autonomous driving is mainly to perceive the 3D/4D environment, detect road conditions and obstacles during vehicle driving, transmit data and signals to the autonomous driving brain, and then make corresponding driving actions. Lidar can be said to be the invisible eye in autonomous driving, and there may be several or dozens of lidars of all sizes on a car. i82ednc

Lidar has many parameters, including laser wavelength, detection distance, FOV (vertical+horizontal), ranging accuracy, angular resolution, output points, wiring harness, safety level, output parameters, IP protection level, power, power supply voltage, laser emission method (mechanical/solid state), service life, etc. i82ednc

The six parameters that provide a significant user experience include detection distance, ranging accuracy, wiring harness, FOV (vertical+horizontal), angular resolution, and output points. i82ednc

The following figure shows several parameters of Huawei LiDAR: detection distance of 220 meters, horizontal FOV of 140 °, and vertical angular resolution less than 0.1 °. If you are not familiar with LiDAR, you will definitely feel dizzy. i82ednc

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

i82ednc

Huawei LiDAR i82ednc

Next, we will explain the parameters related to the user's intuitive perception one by one: i82ednc
1. Detection distance i82ednc
The detection distance is easy to understand, which refers to the range or radius that LiDAR can detect. i82ednc

The ranging ability of LiDAR is related to the reflectivity of the measured object. Reflectivity is the ratio at which the laser that reaches the target object can be reflected back. i82ednc

The higher the target reflectivity, the more effective echoes the radar can detect, so the distance that can be measured is farther. i82ednc

So the detection distance generally appears together with reflectivity, for example, 150 meters @ 10%, which means the detection distance is 150 meters when the target reflectivity is 10%. i82ednc

Talking about detection distance, not just reflectivity, is just playing pranks! Of course, the parameters of Zhonghua in the above figure do not have reflectivity, so it is estimated that the product has not yet been finalized when writing the film. i82ednc

2. Detection accuracy i82ednc

Detection accuracy refers to the accuracy of the detection distance, generally measured in centimeters. The higher the detection accuracy, the more accurate the 3D depth of field characterization. i82ednc

3. Wire harness i82ednc

Lidar is divided into single beam and multi beam. i82ednc

A single beam LiDAR only has one laser emitter, which forms a horizontal scanning line as the radar rotates, so it can only detect obstacles ahead. i82ednc

Multi line LiDAR has multiple laser emitters in the vertical direction, which form multiple horizontal scanning lines as the radar rotates, allowing it to scan a plane. i82ednc

As shown in the following figure: i82ednc

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

i82ednc

i82ednc

For example, a single wire harness is like touching an object with one finger, while a multiple wire harness is like touching an object with the entire palm or even both hands. i82ednc

Obviously, the more wire harnesses there are, the more detailed the characterization of the target object is, and of course, the more expensive the price is. i82ednc

4. FOV (Horizontal Vertical) i82ednc

This is the detection field of view, including both horizontal and vertical directions, just like when we turn on a flashlight and shine on a wall, the range covered by light energy is the same. i82ednc

Mechanical LiDAR can rotate 360 °, so the horizontal FOV is 360 °. The horizontal FOV of solid-state LiDAR will be smaller, for example, the Huawei 120 ° model is already considered a large viewing angle. The larger the horizontal FOV, the wider the range that can be detected. i82ednc

Vertical FOV is only useful for multi beam LiDAR. It refers to the angle formed by the top laser beam and the bottom laser beam. i82ednc

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

i82ednc

i82ednc

The field of view of a vertical FOV is generally inclined towards the underground, for example, if it is 0 ° horizontally, then it is 15 ° upwards and 25 ° downwards, resulting in a vertical FOV of 40 °, as shown in the following figure. The advantage of this is that it allows vehicles to detect more ground vehicles and pedestrians. i82ednc

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters

i82ednc

i82ednc

5. Corner resolution i82ednc

The angular resolution, like FOV, is also divided into two directions: horizontal and vertical. i82ednc


Horizontal resolution refers to the angle formed by the two scanned laser points on the left and right sides; Due to the rotation of the LiDAR and the fact that the laser emitter is a pulse, the targets are shot at one point at a time. i82ednc
Laser pulses have a fixed frequency, so the resolution in the horizontal direction is only related to the radar rotation speed. As long as the speed is slow enough, the resolution can be very high. Now achieving 0.01 ° is also normal. However, slow scanning speed can also affect the rate of information collection. So the horizontal resolution needs to correspond to the determined scanning speed, which is generally expressed in frequency, that is, how many times to scan back and forth in 1 second. i82ednc

Vertical resolution refers to the angle between the laser points formed by the upper and lower wire harnesses. The wiring harness is not uniformly distributed in the vertical direction, but is dense in the middle and sparse in the top and bottom, as shown in the following figure. This is also easy to understand, as pedestrians or obstacles are more likely to be detected in the middle. i82ednc
Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters
Lidar is about to explode, can you understand it? Scientific Popularization Lidar Index Parameters
i82ednc
i82ednc
The vertical resolution claimed by general manufacturers is obviously the resolution of the densest part. For example, a 64 wire product has a vertical FOV of 40 °. If the wiring harnesses are evenly distributed, the vertical resolution is 0.625 °. But in reality, manufacturers calculate based on the dense part, claiming a vertical resolution of 0.2 °. The vertical resolution on Huawei film is 0.1, which also refers to the densest part. i82ednc
6. Output point i82ednc
Also known as periodic acquisition points, for example, a 64 line LiDAR with a horizontal FOV of 120 ° and a horizontal resolution of 0.2 ° at a scanning frequency of 10Hz. i82ednc
We can know that the laser can produce 64 points at once, and scanning at 120 ° can produce 64x120/0.2=38400. Scanning 10 times in 1 second results in a total of 384000 pts/s. i82ednc
Obviously, the more points produced, the better the scanning effect, which is the same as machine gun scanning. i82ednc
Mastering the six core parameters above means mastering the essence of LiDAR. i82ednc
Give another example to explain the overall situation, and compare the learning of a student: i82ednc