Before talking about the working principle of VLP-16, let's clarify the concept of lidar:
Q: What is lidar? How is lidar different from a camera?
A: LiDAR is a sensor based on laser ranging technology. Many people write LiDAR as LIDAR. Note that "i" is lowercase. By measuring the time interval of laser emission-reflection-reception, the distance from the laser transmitter to the object point can be calculated according to the speed of light. If the coordinate system is established with the center of the laser radar, the three-dimensional coordinates of the ground object points can be calculated according to the horizontal angle and pitch angle when the laser is emitted. In the images collected by the camera, 3D information cannot be obtained directly, and it is necessary to estimate the true depth through two or more images with overlapping. The advantage of lidar lies in reliability and high precision, and the advantage of camera is that it has color texture information and low cost.
Q: What is the difference between lidar and radar?
Lidar is a kind of radar (radar), because it uses laser ranging technology, it is called lidar. There are millimeter wave radar, microwave radar and so on. Millimeter-wave radar is a commonly used sensor in the field of automobiles and safety monitoring. It can measure the speed and distance of dynamic objects. Equipping millimeter-wave radar on passenger cars can greatly improve the safety of vehicles. 4D millimeter-wave radar has many similarities with lidar in terms of data, and because of its low cost, it has become a new star in the field of unmanned driving.
Q: What is the difference between lidar and laser scanner?
A: Laser scanner is a commonly used instrument in the field of surveying and mapping. The two instruments are also very similar in principle, because both are based on the principle of laser ranging, and the hardware is based on the laser transmitter, and the measurement results are all three-dimensional coordinates of the scene. The main difference between the two lies in the difference in mechanical structure and use. In terms of mechanical structure, a laser scanner usually has only one laser emitter, which can scan a line through a rotating emitting prism. If the whole machine also rotates on another degree of freedom, it can scan to obtain a complete 360° range. The multi-line lidar in the laser scanner is equipped with multiple lasers at the same time, which also needs to rotate in one degree of freedom. The main function of radar is to detect and perceive the dynamic and static conditions of the scene. Laser scanners focus on 3D modeling of static scenes, and generally the accuracy of laser scanners (millimeter level) is also higher than that of lidar (centimeter level).
Q: What is the difference between mechanical lidar and solid-state lidar?
The laser can only emit one point at a time, how to make the laser collect the information of the whole three-dimensional space? Mechanical lidar and solid-state lidar have taken two completely different paths. Mechanical lidar: one laser not enough? Then add a few more, so multiple lasers are stacked together, but the cost is too much to bear, what to do, turn it up, the laser emitter rotates while firing, so that a circle of 3D points can be obtained. Because it has a mechanical rotating structure inside, this type of lidar is called a mechanical lidar. The difference between multi-line and single-line is the number of internally stacked lasers. The way of solid-state laser is to use the technology of micro-electromechanical system to drive the rotating mirror, and make the laser beam point to different directions through reflection. Involves more physical knowledge such as MEMS and electronic circuits. At present, the mechanical technology is relatively mature and works relatively stably. The solid-state scanning speed is fast, the resolution is high, the volume is small, and the cost is low, which is the future development trend.