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Mobile Robots
Published in Bogdan M. Wilamowski, J. David Irwin, Control and Mechatronics, 2018
Miguel A. Salichs, Ramón Barber, María Malfaz
Rangefinder sensors are usually based on ultrasound or laser signals. The operation of ultrasound sensors consists of emitting a pulse of ultrasound and measuring of the time (designated time of flight) elapsed until the echo is received. The advantages of ultrasound sensors are operational simplicity and price. Therefore, one can assemble a set of sensors to cover a large surface at a relatively low price. The usual physical layout of sensors is to form a ring around the robot. The factors to consider when designing a perceptual system based on sensors of this type are the maximal and the minimal distance that covers the sensor and the dispersion angle of the wave. These kinds of sensors have several disadvantages such as multiple reflection paths, variations of sound speed, echo intensity highly decreases with the distance to the object producing the echo, low resolution due to the dispersion angle, a possible interference among the sensors of one robot and the sensors from the other robots, the dependency on the geometry of the surface of the objects producing the echo, the dependency on the acoustic characteristics and size of the reflected object, and the incident angle.
Terrestrial Laser Scanners
Published in Jie Shan, Charles K. Toth, Topographic Laser Ranging and Scanning, 2018
Gordon Petrie, Charles K. Toth
The LARA laser rangefinder that was used in the original Imager 5003 and 5006 scanner instruments employed a Class 3R continuous wave (CW) laser that operated in the near infrared part of the spectrum at λ = 780 nm. In the earliest Imager 5003 model, the rangefinder was available in two alternative versions giving maximum possible ranges (or ambiguity limits) of 25.2 and 53.5 m, respectively (Mettenleiter et al., 2000). A detailed investigation into the accuracies of the distance and angular measurements of the Imager 5003 was made by Schulz and Ingensand (2004) of the ETH, Zürich. The later Imager 5006 model had an improved maximum range (or ambiguity limit) of 79 m. The accuracy in distance quoted by the manufacturer was ±6.5 mm over a range of 25 m. This instrument continues to be sold currently (in 2016) as the Imager 5006h model, being marketed as a lower cost, entry-level scanner for first-time users. Another variant is the Imager 5006EX model (Figure 2.3a), part of which is encased in a special protective jacket and is designed to be used in areas such as mines and chemical plants in which there is a potentially explosive environment. This specialist Imager 5006EX scanner model is also still available for sale in 2016.
Terrestrial Laser Scanners
Published in Jie Shan, Charles K. Toth, Topographic Laser Ranging and Scanning, 2017
Gordon Petrie, Charles K. Toth
Besides the LMS-Zxxx series of scanners, over the last decade, Riegl has also manufactured a series of long-range laser profile measuring systems. In 2008, it introduced the latest model in the series, which is called the LPM-321 profiler. This has a very different mechanical and optical design to that of the LMS-Zxxx scanners with the laser rangefinder unit mounted on the horizontal (trunnion) axis of the instrument, supported by a single pillar (Figure 3.19a). The rangefinder can measure ranges up to a maximum distance of 6000 m to targets with 80% reflectivity (without the use of a reflector) and can be operated to measure profiles either manually or in an automated mode. It also offers a full waveform digitizing capability in the same manner as an airborne laser scanner. In its automated mode of operation, the LPM-321 can measure up to 1000 points per second. The instrument has a sighting telescope with up to 20× magnification that sits on top of the rangefinder and can have a calibrated digital camera fitted to the side of the rangefinder (Figure 3.19b).
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.