ABSTRACT
Since the mid-1990s laser scanning or light detection and ranging (Lidar) has matured into a sophisticated mapping technology routinely used for 3D modelling of cities, power stations and factories; power line mapping; dike and dune inspection for flood prevention; monitoring of forests, open pit mines, construction sites, tunnels and glaciers; and many other applications. A laser scanner emits laser beams for measuring: (1) range – distance from the sensor to the first surface hit by the laser beam; (2) scan angle; and (3) intensity of the return. These measurements combined with GNSS (Global Navigation Satellite System) 3D positioning and the inertial measurements unit (IMU) result in accurate 3D coordinates of object points. To further improve the accuracy and to transform the 3D coordinates to a common reference frame, registration of the diverse scans and ground control points (GCP) are required. Lidar sensors can be mounted on a wide variety of platforms, including vehicles, the human back and manned and unmanned aircraft and helicopters. This chapter first elaborates on basics of laser light and point clouds, then continues with georeferencing, followed by the principles of airborne Lidar and ground-based Lidar and a comparison of their point characteristics.
