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Laser scanning is an active, distance-based surveying process based on the measurement of the travel times of laser rays (LiDAR technology – Light detection and ranging). The function of a laser scanner is based on the emission of laser light under a known deflection angle, which is reflected from the surface of an object and detected again by the scanner.
In this way the sensing of the surface by the laser beam can record the exact location of millions of points in a very short time. Imaging laser scanners also record an intensity value for each point, which provides information about the type of surface depending on its reflective properties. The raw product is a high resolution, three-dimensional point cloud of the scanned surface or the scanned object, from which appropriate software programs can produce and analyse realistic and practical surface models.
Voit Klaus, Priv.-Doz. B.A. Dipl.-Ing. MMMag. Dr.
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The scanner automatically scans 360° or the desired field and covers a nearly spherical overall view of its surroundings. Since laser scanning is an active system and the light ray to sense the surface is emitted by a laser, this surveying method can still be used in poor light. The measurements are made very quickly and only take a few minutes. The scan resolution (number of recorded points) can be configured depending on the requirements of a specific project (including the surveying accuracy). With increasing distance between scanner and surveyed object. It is also possible to register the colour of the surveyed points and thus assign colour information to the laser data. Such colouring is implemented by an RGB colour overlay of the 3D point cloud, with the colour information recorded by a colour camera. The laser scanner used in this example has an internal colour camera with a maximum resolution of 70 Megapixels. The colour overlay is very exact with a precision of a few pixels.
Terrestrial – as well as airborne – laser scanners for the representation of objects or the remote investigation of the surface of the earth using pulse laser technology have already been successfully used since the 1990s and have meanwhile become an essential data basis for the most varied professions. The surveying rate is now up to 300,000 points/s, from a distance of some kilometres (strongly dependent on the properties of the object and the environment).
The production of high-resolution 3D colour images is now a common instrument in the costruction sector, architecture or forensic science. Furthermore, 3D-laserscanning plays an important role in tunnel construction to completely detect the cavity geometry. For geological questions, 3D-laserscanning is mainly used for natural hazard monitoring. By comparison of multiple scans, unstable slope areas can be detected and its deformation speed can be recorded. On the basis of the 3D-terrain-model obtained by the lasers-scanning, further modelling with regard to slope stability or rockfall can be performed.