Airborne LiDAR measurement technology will be one of the future development directions of measurement. It has many unique advantages. It can fully meet the accuracy requirements of the survey and design of transmission lines, railways, and highways, and can effectively improve the efficiency of survey and design.
1 Introduction to LIDAR Technology
LIDAR technology can obtain various surface data. The laser it emits can penetrate the vegetation on the ground, and after removing the vegetation and ground objects on the ground, it can generate the digital elevation model (DEM) data of the ground. Using DEM data and the exterior orientation elements of the aerial digital image obtained by differential GPS and INS, the aerial digital image can be orthorectified to generate an orthophoto map. It can also classify and obtain information on ground features, roads, and vegetation. LIDAR technology measurement requires only a few synchronization control points and a small amount of field adjustment and mapping work.
Airborne Lidar (Light Detection And Ranging) technology is an automatic earth observation technology. After integrating advanced technologies such as inertial navigation unit, global satellite positioning system, laser ranging, etc., it continuously emits laser pulses and passes through ground objects. After reflection, it is collected by the receiving unit of the observation system, and then the surveying and positioning of the three-dimensional geographic information on the surface is completed accurately and quickly. For airborne laser point cloud data processing software in China, the TerraSolid series software from Finland is usually selected. The software is developed based on the MicroStation channel and inherits the channel's excellent graphics operation, vector drawing and picture display functions. The TerraMatch, TerraScan, and TerraModeler modules are mainly used when processing DEM. Among them, the TerraMatch module completes the point cloud data calibration function; the TerraScan module completes the point cloud data management, classification filtering, point cloud editing, effect output and other functions; the TerraModeler module does not The surface model generation and visualization functions of regular triangulation, grid, and shaded maps play an important role in the manual and accurate classification and quality control of point clouds. The airborne lidar technology has the advantages of high accuracy and fast speed in obtaining DEM data. However, in areas with lush vegetation on the ground, there is often a phenomenon of laser beams that cannot penetrate the vegetation, making the dense vegetation underneath, often defects and fewer spots, making the construction The shape of DEM is distorted, which greatly increases the workload of manual classification.
2 Features of Airborne LiDAR Technology
2.1 Structure and working principle of the airborne LiDAR system
Airborne Lidar (Light Detection And Ranging, LiDAR) is an advanced remote sensing data acquisition system, which is mainly composed of a flight platform, laser scanner (LaserScanner), positioning and inertial measurement unit (GPS+INS), CCD camera and control The unit consists of five parts. Among them, the control unit is a key part of the airborne lidar system, and its core role is to keep the entire system synchronized and coordinated.
2.2 Comparison between LiDAR technology and traditional aerial survey technology
In view of the high efficiency, initiative, penetration, high density, high precision, and rich characteristics of airborne LiDAR technology, compared with traditional aerial photogrammetry technology, airborne LiDAR measurement technology has the following advantages: ①It can be significant The survey and design cycle is shortened, and initial survey and fixed survey can be completed at one time to meet the design requirements of construction drawings; ②It is less restricted by weather, generally not affected by clouds, sun altitude and visibility, and the number of working days is significantly increased; ③covered by vegetation The image is small, and the penetrability of lidar can be used to improve the elevation accuracy of ground measurement; ④ In addition to a small amount of manual intervention, it is easy to realize automatic data processing.
3 Application of airborne lidar technology in power engineering
3.1 Power line selection
The first intention of power optimization line selection is to make the line layout more reasonable and economical while minimizing the impact on the surrounding environment of the line, and then achieve the intention of saving construction and operating costs.
The method of using airborne lidar technology to optimize the line selection of overhead power transmission lines (see the figure below) is rough as follows: First, use the existing small-scale topographic map or satellite remote sensing image data to start selecting a better transmission line Path; secondly, according to the preliminary selection path, airborne lidar is selected for full-line measurement, forming data results such as DEM, DSM, DOM, etc.; finally, through the professional software developed by our company (lidar transmission line optimization and plane-section formation The map system) loads lidar data, completes route optimization, comparison and selection, and outputs final results such as route diagrams, plan diagrams, cross-sectional diagrams, demolition statistics, and crossovers.
3.2 Power line inspection
my country’s rapid economic development, uneven development and uneven distribution of energy, has increased the demand for long-distance, ultra-high-voltage transmission lines. After some transmission lines are built, it is necessary to inspect the lines and find the lines for safe and efficient work. Safety hazards to prevent accidents. In the traditional inspection process, despite the investment of a lot of manpower, material and financial resources, due to the influence of the climate and the environment, the work efficiency and effect are not satisfactory. Especially for some ultra-high voltage line inspections, the effect is very limited. More advanced inspection methods to complete. Airborne lidar technology can fulfill this requirement well. When the airborne lidar measurement system performs circuit inspections, it obtains the laser point cloud of the line and the surface of the object, which reflects the three-dimensional space condition of the transmission line. Through the laser point cloud data, it can be judged whether various targets meet the requirements of safe operation of the line (See below). The primary identification objectives in power inspections are as follows: one is the minimum distance between the transmission line and nearby objects (trees, houses, etc.); the second is the displacement of the tower base; the third is the conductive line and surrounding objects under strong wind conditions The minimum spacing etc. It can be seen that the airborne lidar measurement system can obtain more accurate and detailed information on the line corridor, and is an ideal line inspection method.
3.3 Point cloud data classification
The large number of three-dimensional discrete point data acquired by airborne LiDAR technology is very dense, and is often referred to as "point cloud". Since the point cloud data contains all the reflective ground, buildings, vegetation and other information on the ground, it is necessary to classify the point cloud data to extract different height attributes such as ground, vegetation, and buildings in order to carry out later applications. The data. The principle of laser point cloud classification is based on the comparison of the elevation of the laser point and the surrounding points. At present, many LiDAR post-processing software (such as Terrasolid) provide the function of automatic laser point cloud classification, but to obtain better classification results, often A certain amount of manual intervention is required, especially in areas with dense mountain vegetation. In the survey and design of railways and highways, the final result to be obtained is a digital ground model, that is, only the laser data of ground points are needed, so the ground and non-ground laser points in the laser point cloud need to be classified. The classified surface data are discrete points with three-dimensional coordinate values. After constructing the TIN, DEM can be generated according to the specified gridwww.isurestar.net