Answering some question about automated point cloud porcessing
LiDAR stands for Light Detection and Ranging. It is a surveying method based on the measurement of the distance from a sensor to an object using laser light. LiDAR is often called 3D laser scanning.
ALS stands for Aerial Laser Scanning and refers to LiDAR scanners mounted on aerial vehicles such as airplanes, drones or helicopters. This technology is operative nowadays thanks to the combination of LiDAR, Global Positioning Systems (GPS) and Inertial Measurement Units (IMU).
TLS stands for Terrestrial Laser Scanning and refers usually to a fixed scanner in a tripod. These systems have been operating since the 80s and have reached a level of maturity that enable a widespread deployment. It is possible to use several fixed scanners at different locations and register their individual scans in order to obtain a dense and complete 3D point cloud. On the one hand, TLS is usually the most accurate acquisition system. On the other hand, TLS acquisitions may be very expensive in large scale applications due to the high number of fixed stations needed to cover a large area
MLS stands for Mobile Laser Scanning and refers to LiDAR scanners mounted on terrestrial vehicles such as cars, trains, among others. This technology is operative nowadays thanks to the combination of LiDAR, Global Positioning Systems (GPS) and Inertial Measurement Units (IMU). Mobile mapping technology unlocks the productivity problem of TLS systems being suitable for large scale applications in urban, highway and railway environments.
Time of Flight (ToF)
Measurement of the time taken by the laser beam to travel from the scanner to the object and come back. Since the speed of light is known, the ToF allows to compute the distance between the scanner and every object in the scene.
Point cloud density
It is an indicator of the point cloud resolution. It is usually expressed as number of points per square meter. High density means many points and much information. Note that storing more points requires bigger point cloud files. In practice, point cloud density is variable and depends on several factors such as scanner resolution, vehicle speed, distance from objects to scanner, objects geometry and material, etc.
LAS is one of the most common formats for exchanging points clouds. Versions 1.2 and 1.4 are the most widely used. LAZ is a compressed version of LAS.
ASPRS is the American Society for Photogrammetry and Remote Sensing. It maintains the LAS format and defines a standard to manage classified point clouds.