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A 3D laser scanning technique and its application to rock mechanics and rock engineering
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Scanners can also be divided into three different types according to their scanning principles, summarized below: Pulse-based scanner. The pulse-based scanner is also called a time-of-flight (TOF) scanner, and is an active scanner that uses laser light to probe the subject. At the heart of this type of scanner is a TOF laser rangefinder. This finds the distance to a surface by timing the round-trip time of a pulse of light, as shown in Figure 2a. Clearly, the accuracy of a TOF 3D laser scanner depends on how precisely we can measure the time t. The laser rangefinder only detects the distance of one point in its direction of view. Phase-based scanner. In comparison to the pulse-based scanner, this type of scanner has a high-speed scanning rate and better accuracy. Here, the transmitted beam is modulated by a harmonic wave and the distance is calculated using the phase difference between the transmitted and received waves. The phase-based scanner has higher precision, and higher measurement rates of up to one million points per second can be obtained applying the phase shift measurement principle, illustrated in Figure 3. Triangulation-based scanner. Triangulation-based 3D laser scanners are also active scanners that use laser light to probe the environment. This technique, shown in Figure 2b, is called triangulation because the laser dot, the camera and the laser emitter form a triangle.
A 3D laser scanning technique and its application to rock mechanics and rock engineering
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
Scanners can also be divided into three different types according to their scanning principles, summarized below: Pulse-based scanner. The pulse-based scanner is also called a time-of-flight (TOF) scanner, and is an active scanner that uses laser light to probe the subject. At the heart of this type of scanner is a TOF laser rangefinder. This finds the distance to a surface by timing the round-trip time of a pulse of light, as shown in Figure 2a. Clearly, the accuracy of a TOF 3D laser scanner depends on how precisely we can measure the time t. The laser rangefinder only detects the distance of one point in its direction of view. Phase-based scanner. In comparison to the pulse-based scanner, this type of scanner has a high-speed scanning rate and better accuracy. Here, the transmitted beam is modulated by a harmonic wave and the distance is calculated using the phase difference between the transmitted and received waves. The phase-based scanner has higher precision, and higher measurement rates of up to one million points per second can be obtained applying the phase shift measurement principle, illustrated in Figure 3. Triangulation-based scanner. Triangulation-based 3D laser scanners are also active scanners that use laser light to probe the environment. This technique, shown in Figure 2b, is called triangulation because the laser dot, the camera and the laser emitter form a triangle.
The “System” in UAS
Published in Douglas M. Marshall, R. Kurt Barnhart, Eric Shappee, Michael Most, Introduction to Unmanned Aircraft Systems, 2016
Joshua Brungardt, Richard Kurt Barnhart
A laser range finder uses a laser beam to determine the distance to an object. A laser designator uses a laser beam to designate a target. The laser designator sends a series of invisible coded pulses that reflect back from the target and are detected by the receiver. There are, however, drawbacks to using a laser designator on an intended target. The laser may not be accurate if atmospheric conditions are not clear, such as rain, clouds, blowing dust, or smoke. The laser can also be absorbed by special paints or reflect incorrectly or not at all such as when aimed at glass.
Magnitude amplification of flash floods caused by large woody in Keze gully in Jiuzhaigou National Park, China
Published in Geomatics, Natural Hazards and Risk, 2021
Jiangang Chen, Wenrun Liu, Wanyu Zhao, Tianhai Jiang, Zhongfu Zhu, Xiaoqing Chen
Both a hand-held global positioning system (GPS; Garmin GPSMAP, Taiwan, China) and laser rangefinder (Contour XLRic, Contour Company, USA) were used to determine the locations and extents in the field investigation. The laser rangefinder had a maximum range of 1,850 m and a measurement accuracy of 0.10 m (Chen et al. 2015). The geomorphological conditions suggested that the accuracy of the deposit volume measured by using the ground penetrating radar system with a measuring error of 1 m was sufficient for the purpose of our work (Tang et al. 2012). Whether the LW moves or not can be determined by two ways: (1) according to the relative distance between the LW centre and a fixed position on the banks and (2) comparing the UAV images from different periods. We measured the length and diameters of the LW pieces scattered in the gully with tapeline (as shown in Figure 2), and the space between standing trees as also measured by tapeline. The average length was obtained by measuring the length of the LW at its three positions: the top and the surface towards and away from the stream. The circumference of the LW was measured at both ends and in the middle, and then the average diameter was obtained through the formula where C is the circumference, D is the diameter and π is the circular constant. A camera was utilized to photograph the driftwood distribution state.
Influences of a debris flow disaster chain on buildings in remote rural areas, Southwest China
Published in Geomatics, Natural Hazards and Risk, 2022
Lu Zeng, Yonggang Ge, Jiangang Chen, Fenghuan Su, Huayong Chen, Wanyu Zhao, Guangwu Si
Both a hand-held GPS instrument (GARMIN GPSMAP, Taiwan, China) and a laser rangefinder (Contour XLRic, Contour Company, USA) were employed to determine the location and damage scope of buildings related to the disaster chain. The laser rangefinder had a maximum range of 1850 m and a maximum measurement accuracy of 0.10 m, and the same rangefinders have been adopted in geological hazard surveys after the Wenchuan and Jiuzhaigou earthquakes and onsite investigations of large-scale debris flow disasters (Chen et al. 2015, 2018). A camera was utilized to photograph the damage state. Both unmanned aerial vehicles (UAVs) and pre- and postdisaster remote sensing images are important ways to quickly determine disaster conditions. These methods have been adopted to determine the distribution of landslides and collapses after earthquakes and have been widely applied in rescue work during debris flows and flash floods (Chen et al. 2017; Tziavou et al. 2018). A UAV (Inspire 2, DJI-Innovations, China) was utilized to acquire photographs along the Meilong gully and the XJCR, which has a length of 6 km. A total of 1010 UAV photos were captured, the maximum flight height was 500 m, and the acquired images were then used to construct a topographic and geomorphic map for further analysis, resulting in a postdisaster image (with a resolution of 0.1 m). The predisaster image used the Gaofen-2 satellite images (China) obtained in April 2018, with a maximum spatial resolution of 0.81 m. Both images were used to determine the relative building location and size and the cultivated area, and the siltation state of the XJCR was also determined by comparing pre- and postdisaster images.