Airborne lidar (LiDAR) is a measuring equipment which integrates laser scanning and positioning and attitude determination system. It can locate the spot of laser beam hitting the object with high accuracy. The LiDAR system consists of a laser and a receiving system. The laser produces and emits a beam of light pulses, hits the object and reflects back, and is eventually received by the receiver. The receiver accurately measures the propagation time of the optical pulse from its emission to its reflection. Since the speed of light is known, the propagation time can be converted to the measurement of distance. Combined with laser height and laser scanning angle, the three-dimensional coordinates X, Y and Z of each ground spot can be calculated accurately. Lidar equipments suitable for different application scenarios, such as airborne, vehicle-borne, ground fixed station, and hand-held, have also been reported recently on new technology products of space-ground integrated miniature lidar. In recent years, the application of large and medium-sized airborne lidar systems in power grid industry shows that they usually integrate an optical camera with a vertical angle of view for synchronous acquisition of ground images or coloring of laser point clouds to achieve better visual effect. Lidar technology has emerged in the application of transmission lines at home and abroad, and has been recognized.
Lidar has the ability to penetrate vegetation and can measure the topography under vegetation cover. At the same time, the high-precision point cloud data obtained by lidar has high measurement accuracy, which is suitable for high-precision topographic survey and engineering survey, three-dimensional measurement and modeling of transmission lines and channels, and engineering survey applications requiring high accuracy. However, the equipment of lidaris still expensive.
In the power industry application, oblique photography has shown certain application potential, but it has not yet been successfully deployed in power inspection and 3D measurement. The following figure shows the transmission line and substation data collected and automatically modeled at a flight altitude of 120 meters using a 5-lens oblique camera with a multi-rotor drone. Since oblique photography data acquisition requires overlapping of navigation belts (60-80%), multiple flights are required to obtain 3D data of the power corridor, so the collection efficiency is slightly lower. From the effect of automated modeling, the modeling effect of large scene objects such as factory buildings and roads is very good, but the modeling effect of small objects such as electric towers and power lines is not good, the tower is distorted, and power line loss cannot be modeled (as shown in the figure below).
The application of airborne lidar technology in transmission line inspection has been mature, and there are many cases at home and abroad. Because of its high measurement accuracy (up to centimeter level), it can also obtain penetrating vegetation, and can also achieve accurate measurement and modeling of small objects such as wires and towers. Especially in power inspection and "three-span" measurement applications show great accuracy advantages. The following picture shows a unit using UAV-mounted lidar system to obtain color laser point cloud and classified modeling data at 120 meters flight altitude. The density of laser point cloud reaches 110 points per square meter. From the data effect of automated modeling, although texture is slightly lower than tilt photography, it also has good visualization effect. At the same time, line sag and crossover distance can be prepared for measurement.
Oblique photography and lidar technology, as a new means of data acquisition in 3D space, have their own advantages and disadvantages in various applications in the power grid industry. Combined with research and interviews with industry experts, the conclusions are as follows:
1. Lidar technology has obvious advantages in measurement accuracy and power facility modeling and is very suitable for typical power grid applications such as power inspection and “three-span” measurement. The price of laser radar equipment is also getting lower and lower, and the camera can also be used to obtain high-reality visual effects;
2. Oblique photography technology has certain advantages in equipment and 3D visualization effects, but data processing takes a long time and high cost, and has defects in modeling and measurement accuracy of the electric tower and power line. It requires a lot of manual intervention in data processing to accurate 3D modeling and measurement of electrical facilities;
3. Oblique photography and laser radar have strong complementarity in technology. The fusion of the two technologies in the future is a development direction. However, there is no mature combination scheme yet, and a lot of basic research is needed to realize it.
The integration of the two technologies is unified and complemented in the three-dimensional real-world application of transmission lines.