LiDAR(Light Detection and Ranging) Yes Abbreviation for laser detection and ranging system. The working principle is to transmit a detection signal (laser beam) to the target, and then compare the received signal (target echo) reflected from the target with the transmitted signal, and after appropriate processing, information about the target can be obtained, such as Target distance, azimuth, altitude, speed, attitude, and even shape parameters to detect, track, and identify targets.
What is the number of laser radar lines
We often hear 16-line laser radar, 64-line laser radar, then what is the number of laser radar lines?
The number of laser radar lines is the number of laser emitters distributed in the vertical direction. The multi-line laser radar is a distribution of a plurality of laser beams by vertical rotation of a plurality of laser emitters. In theory, the more Lidar harnesses, the denser the description of the environment is more fully.
Laser scanning principle
Ranging method: Time of Flight
1. Laser in laser radar emits a bundle Ultrashort laser pulse
2. After the laser is projected onto the target object, the diffuse reflection sensor receives the diffuse reflection laser.
3. The target is accurately calculated by the flight time of the laser beam in the air. Object to sensor distance
d : distance ; c : speed of light; t : time from laser to retraction
Since the laser transmitter or receiver is mounted fixed, very clear resolution can only be achieved in very concentrated areas. In order to expand the field of view, a single transmitter and receiver are typically required to deflect up or down to achieve greater laser field of view coverage. For example, Velodyne’s 64-line lidar system has a vertical viewing angle of 26.8 degrees, which allows the lidar to see the top of a 12-meter-high object from 50 meters away.
In addition to the distance from the radar, the density of the point cloud is different. The closer the interval is, the denser the point cloud is, the farther the point cloud is, the more sparse the point cloud is. Rough.
Lidar parameter parameters
Measurement distance, measurement accuracy, measurement rate, and angular resolution are several important indicators for determining the performance of 3D laser radar.
The measurement distance determines how far the unmanned vehicle can see. In theory, of course, the farther the better.
The accuracy of the measurement determines the accuracy of the unmanned vehicle. The more accurate the unmanned vehicle is, the more reliable it is.
The angular resolution determines how much the unmanned vehicle can look, and the more detailed the algorithm, the more accurate it can be.
Comparison of Lidar and other sensors in the driverless field
The price of lidar is high. Take the velody 64 line as an example. The price is 8W US dollars, which is unacceptable for mid-to-low end production cars. With the large-scale popularization of laser radar, the price is still very promising.
2) Rain and snow weather
Because of the precise measurement accuracy of the lidar, it can recognize rain, snow and even haze as obstacles, causing many problems for driverless driving.
3) Measuring distance
Another challenge for lidar systems is that the refresh rate during rotation is relatively slow. The refresh rate of the system is limited by the speed of rotation of complex optics. The fastest rotation rate of a lidar system is approximately 10 Hz, which limits the refresh rate of the data stream. When the sensor rotates, the car traveling at 60 mph travels 8.8 feet in 1/10 seconds, so the sensor is largely invisible to the changes that occur within 8.8 feet of the car during the drive. More importantly, the range covered by the lidar (in perfect conditions) is 100-120 meters, which is equivalent to less than 4.5 seconds of travel time for a car traveling at 60 mph.
4) Interference and Attack
The laser emitted by the laser radar itself is uncoded. So the receiver itself has no way of identifying whether the light is emitted by its next-door transmitter or an interference signal. Hacking refers to the use of signals simulating vehicles and pedestrians, and feedback to the laser radar to create an attacking illusion of obstacles around it. Eventually the car will be forced to slow down or brake.