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 lidar is still expensive.
In the application of power industry, tilt photography has shown a certain application potential, but it has not been successful in power inspection and three-dimensional measurement. The following picture shows the transmission line and power station data collected and automatically modeled by a unit with a 5-lens tilt camera mounted on a rotorcraft UAV at a flight altitude of 120 meters. Because the data acquisition of tilt photography requires overlapping airstrips (60-80%) and multiple flights to acquire three-dimensional data of power corridor, the acquisition efficiency is slightly low. From the point of view of the effect of automation 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 poles and towers are distorted, and the loss of power lines can not 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.
Tilt photography and lidar technology, as new means of acquiring three-dimensional spatial data, have their own advantages and disadvantages in various applications of power grid industry. Based on the investigation and interview of 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 patrol and "three-span" measurement. The price of lidar equipment is also getting lower and lower. Combining with the camera, it can also get high realistic visualization effect.
2. Tilt photography technology has some advantages in equipment and three-dimensional visualization effect, but the data processing is time-consuming and costly. At the same time, it has shortcomings in tower and power line modeling and measurement accuracy. It requires a lot of manual intervention in data processing before it can be applied to accurate three-dimensional modeling and measurement of power facilities.
3. Tilt photography and lidar have strong complementarity in technology. Fusion and application of the two technologies in the future is a development direction. But at present, there is no mature combination scheme, and a lot of basic research is needed to achieve it.
The integration of the two technologies can complement each other in the application of three-dimensional reality of transmission lines.