Laser Scanning
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Land Administration System Cadastre
Land Cover Change Detection
Laser Scanning G EORGE VOSSELMAN ITC Department of Earth Observation Science, International Institute for Geo-Information Science and Earth Observation, Enschede, The Netherlands
Change Detection
Synonyms
Land Information System
Laser altimetry (in case of airborne platforms); LiDAR; Light detection and ranging
Cadastre
Definition
Land Policy Cadastre
Land Registry Cadastre
Land Use Planning and Environmental Modeling
Laser scanning is a surveying technology for rapid and detailed acquisition of a surface in terms of a set of points on that surface, a so-called point cloud. Laser scanners are operated from airborne platforms as well as from terrestrial platforms (usually tripods). Operated from airborne platforms the pulses emitted by a laser range finder reflect on the Earth’s surface and objects thereon and are again received by the laser range finder. The time elapsed between emitting and receiving a pulse is multiplied by the speed of light to derive the
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Laser Altimetry (in Case of Airborne Platforms) Laser Scanning
Laser Scanning, Figure 1 m2
Point cloud with a point density of 15 points/
610
Laser Scanning
distance between the laser range finder and the reflecting object. This distance is combined with position and attitude information of the airborne platform, as well as the pointing direction of the laser beam, to calculate the location of the reflecting object. A rotating mirror is used to deflect the laser beam in directions perpendicular to the flight direction. Thus a swath below the flight path is scanned (Fig. 1). Terrestrial laser scanners are usually operated from a stationary platform such as a tripod. In this case, the horizontal and vertical deflection of the laser beam is controlled by a system of two rotating mirrors. Various ranging techniques are applied for terrestrial laser scanning. Beside the “time-of-flight” principle, as applied by airborne laser scanners, continuous wave (phase measurements) and optical triangulation are used [1]. Historical Background Airborne laser ranging was introduced in the 1960s shortly after the development of lasers. Seeking more effective techniques for topographic mapping of forested areas, laser range finders were combined with inertial navigation systems (INS) in the early 1980s [3]. A few years later the first experiments were conducted with the additional usage of global positioning system (GPS) receivers to improve the positional accuracy [4]. These experiments used only a downward pointing laser and thus only recorded height profiles below the flight path. While these laser profilers could only achieve a high point density in the across-flight direction at the cost of flying many flight lines, the experiments proved the high potential of ranging measurements combined with GPS and INS. In the early 1990s the first scann
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