LiDAR [ Light Detection and Ranging Sensor ]
What is LiDAR ?
Lidar, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances) to the Earth. These light pulses — combined with other data recorded by the airborne system — generate precise, three-dimensional information about the shape of the Earth and its surface characteristics.
Type of LiDAR
Reducing the relative flight height and increase high-density of laser point, we can get greater scale topographic maps use this way. Airborne LIDAR technology is now a proven method for acquiring accurate digital terrain model data and associated imagery under a wide range of conditions.
- Topographic — Maps the land using near IR (Infra-Red) light.
- Bathymetric — uses water-penetrating green light to measure seafloor and riverbed elevations.
Terrestrial laser scanning (TLS), also referred to as terrestrial LiDAR (light detection and ranging) or topographic LiDAR, acquires XYZ coordinates of numerous points on land by emitting laser pulses toward these points and measuring the distance from the device to the target mapping buildings, natural features, trees at ground level.
- Static Laser Scanning — Static laser scanners are sophisticated instruments that operate much like high-speed total stations and collect lidar point clouds from a static location. for a more complete explanation static-lidar.
- Mobile Laser Scanning — is a land surveying method that uses laser systems mounted on moving vehicles. MLS systems can be mounted on land-based vehicles such as cars, trains, and trucks; airborne vehicles such as UAVs and helicopters; or boats
Principle of LiDAR
- Laser pulses travel in all direction till the pulse strikes an object/obstacle
- On striking to object, the pulses are reflected in the LiDAR system
- LiDAR registers this echo pulse
- The system calculates the distance of the object based on the laser pulse’s travel time to and from it
Powerful computer to visualize a live, three-dimensional image of the system’s surroundings. When integrating multiple laser transmitters, tracking capabilities are exponentially increased, receiving millions of individual reflection points simultaneously. Constant spontaneous updates build out an astonishing level of data detail and scope.
Through this process, our lidar system can map a multifaceted of its surrounding in real-time, allowing driver assistance systems to make hundreds of carefully calculated driving decisions every minute
- 1D lidar consist of still laser beam that calculate the distance between an obstacle and the scanner on one axe so one dimension.
- 2D LiDAR consist of one laser beam which has a spin(rotating) mechanism, which collect horizontal distance to the targets to get data on X and Y axes.
- For a 3D LiDAR, the idea is the same, but several laser beams are vertically stacked and are shot to get data on X, Y and Z axes. Each laser beam will have an angle delta with the other beams
Features of LiDAR
Field of view : Lidar has 360° FoV. Having wide FoV is important for Autonomous system to navigating safely in environment.
Range : Range is feature which will define how far the objects can be detected.More the range of Sensor , autonomous system will detect the object and take the required action within safety time. At highway speeds , a minimum of 100meters allows the vehicle the time it needs to react to changing road conditions and surroundings.
Resolution : Resolution plays main role to identifying object ; more the resolution , more the information we can get like size , shape and location of objects. High resolution LiDAR is critical for object detection and collision avoidance at all speeds.
Vertical Field of view : Its is another best feature lidar has which helps in real life driving needs. Rather than considering only one plane of object , we need to have information about tall objects , road signs and driving different slops of roads.
Channel size : More the number of channel , better the object created. Below figure show the person detection using Velodyne lidar of puck 32 and puck 16 model, (32 and 16 are the channel of respective lidar) from10 meter distance
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