In the process of digital city construction, airborne lidar technology can be used to obtain high-precision, high-density point cloud data, which constitutes the basic data of a three-dimensional city, and quickly analyze and measure the spatial information of city construction, which is for the establishment of a three-dimensional city Provide necessary data support
The construction of a digital three-dimensional city is an important part of the development of a digital city, which fully demonstrates the achievements of the city in the planning and construction process, and can more efficiently develop and utilize the urban air department. In the process of digital city construction, airborne lidar technology can be used to obtain high-precision, high-density point cloud data, which constitutes the basic data of a three-dimensional city, and quickly analyze and measure the spatial information of city construction, which is for the establishment of a three-dimensional city Provide necessary data support. The airborne lidar technology applies computer technology, fixed location technology and GPS navigation technology, and combines the above technical advantages. It has the characteristics of simple operation, high operating efficiency, high precision, low cost and small workload. It has a wide range of application prospects.
1 technical process analysis
The urban three-dimensional building volume production process mainly includes the following aspects. The first is the preprocessing of point cloud data and the classification of point clouds; the second is the spatial three-dimensional encryption processing of the measured original image, and the formation Digital orthographic image; the last one is to combine the classified point cloud and orthophoto to make the building body bun and digital elevation model. The data processing flow of airborne lidar is shown in Figure 1: 2 Data processing analysis of laser point cloud
Laser point cloud data processing methods mainly include the following aspects. The first navigation trajectory, second, the solution of point cloud data; third, the system circuit will be abnormal during the measurement process; fourth, the splicing of point cloud data and the correction of system errors; Fifth, segment the point cloud data. Sixth, the transformation of the coordinate system. After the measurement is completed, in the process of determining the coordinates, the positioning position determined by the POS dynamic positioning can be attributed to the WGS-84 coordinate system. The next step is to convert the data in the above-mentioned coordinate system to the local coordinate system. In the process of transforming the three-dimensional coordinates to the plane coordinate system, the existing control points that are evenly distributed in the survey area can be used to calculate the coordinates and convert them into fixed parameters, and then the coordinates are determined. The conversion of the elevation system requires the use of the measured level in the survey area. The points can be determined after fitting transformation; finally, the hierarchical point cloud data is effectively classified. There are many types of point clouds in the measurement process. The main content includes ground points, low vegetation points, high vegetation points, and urban buildings. In the process of classifying these point clouds, hierarchical classification strategies and the combination of man and machine are mainly used for classification. For the first classification method, it is necessary to filter and propose the non-ground point cloud according to the corresponding level, and finally extract the bare ground, and then divide the point cloud in the ground into ground points, non-ground points and noise points. After the ground points are stratified, the non-ground points can be further classified and sorted. Extract low-vegetation points, high-vegetation points and building points in the process of classifying and sorting non-ground points. In the process of surveying and mapping urban buildings, the point cloud data is intertwined due to the dense buildings inside the city. Therefore, in the classification process, there may be wrong points. In this case, it is necessary to manually modify these errors to ensure the accuracy of the classification results.
3 DEM generation and building frame model production
First, the generation of DEM. DEM generation mainly includes airborne point cloud denoising, classification and sorting of ground point clouds, water leveling, and grid insertion. In the process of DEM generation, its core work is to classify and organize the ground point cloud data. During the splitting process, the judgment is mainly aided by the three-dimensional rendering effect, the orthographic image and the detailed cross-sectional view; secondly, The production of the frame model of the building body. The production of the frame model of the building body needs to be combined with the data after the classification of the ground point cloud, the spatial three-dimensional encryption results, the original aerial photos, the orthographic image data and the city's graphic data for comprehensive judgment. The first step is to automatically generate a patch model of the roof of the tested building in the corresponding software system. At the same time, it is necessary to correct the shape of the patch and the neighboring Guanshi with reference to the original aerial photo data, and then output the building body frame Model, and then import the frame-moon type of the data to the three-dimensional software to further optimize and edit the frame model to generate the final frame-moment shape.
The application and development of airborne lidar technology provides a brand-new technical means for cities to obtain high-precision spatial information. Its application and development in 3D city construction effectively shortens the time of 3D city construction and improves the efficiency and efficiency of construction. Quality reduces the cost of surveying and mapping, laying a solid foundation for the wide application in 3D city construction.www.isurestar.net