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The biggest advantage of laser radar, four systems, eight indicators
Release time:
2021-07-29
The biggest advantage of lidar: 3D point cloud modeling
Lidar (English Lidar), English full name is Laser Detecting and Ranging, that is, laser detection and ranging.
Similar to radar, lidar works by transmitting and receiving laser beams.
The distance is determined by measuring the time difference and phase difference of the laser signal, the angle is measured by horizontal rotation scanning, and a two-dimensional polar coordinate system is established according to these two parameters, and then the height information in three dimensions is obtained by obtaining different pitch angle signals.
High-frequency lasers can acquire a large number (about 1.5 million) of position point information (called point clouds) in one second, and perform three-dimensional modeling based on this information.
In addition to obtaining position information, the reflectivity of the laser signal can distinguish different materials of the target substance. The more dimensions (line bundles) of the lidar, the higher the measurement accuracy.
Due to the high frequency and short wavelength of the laser, extremely high angle, distance and speed resolution can be obtained.
The high resolution of distance and speed means that Doppler imaging technology can be used to create a clear 3D image of the target, which is the biggest advantage of lidar.
In the second year of the advent of lasers (1961), someone put forward the idea of lidar. In the Apollo 15 mission in 1971, American astronauts used laser altimeters to map the surface of the moon, making people aware of the accuracy of lidar. And practicality, has received widespread attention.
The world's first automotive lidar is a 64-line lidar produced by Velodyne, a US company, which made its debut in the driverless challenge in 2005.
Four systems, eight indicators:
LIDAR = laser emission laser reception information processing scanning system
The following figure shows the composition of the lidar system:
Laser emission system: the excitation source periodically drives the laser, emits laser pulses, the laser modulator controls the direction and number of lines of the emitted laser through the beam controller, and finally emits the laser to the target object through the emission optical system;
Laser receiving system: through the receiving optical system, the photoelectric detector receives the laser reflected by the target object and generates the receiving signal;
Information processing system: The received signal is amplified and converted to digital-to-analog, calculated by the information processing module, obtains the surface morphology, physical properties and other characteristics of the target, and finally establishes the object model.
The scanning system rotates at a stable speed to scan the plane and generate real-time plan information.
Generally, the following eight technical indicators are used to evaluate lidar:
Maximum radiated power: Decide if protection is needed
Horizontal field of view: 360 degree full view rotation
Vertical field of view: pitch angle (30 degrees/15 degrees)
Light source wavelength: optical parameters (nanometer level)
Measurement distance: whether to meet the long-distance detection (200 meters)
Measurement time and frame frequency: the time for the laser to return one turn
Vertical and horizontal resolution: large impact on the algorithm, the higher the accuracy, the more expensive
Ranging accuracy: centimeter level
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