Three-dimensional Topography Measureing Technique Of Structures Based On UAV Oblique Photogrammetry

At present,China is in the rapid development stage of urbanization,and the city's demand for geographic information is increasingly significant.In order to realize the sustainable development of cities,China has put forward the concept of digital city in recent years.As an important part of the spatial information of digital cities,three-dimensional model construction of digital cities has become an increasingly important task for digital city production units.Meanwhile,infrastructure construction in China,especially large infrastructure,is also in rapid development phase.In order to guarantee the control of catastrophe during infrastructure construction and operation period,the life-cycle monitoring of infrastructure must be carried on.However,the traditional monitoring technology seems insufficient for extremely large structures,so a kind of rapid access to geospatial data and a new method of real-time updates are urgently required.Therefore,this paper relied on the national key research and development project "coastal major infrastructure monitoring and perception technology and dynamic information platform facing complex environment"(project number: 2016YFC0800207),and carried out the following work on the construction and precision evaluation of the three-dimensional topography:(1)A comparative study of the key steps in the construction process of the threedimensional topography has been carried out,and a set of real-scene model construction method based on UAV tilt photogrammetry has been proposed.The key steps have been optimized to realize automation and visualization in the process of model construction.(2)A large number of field tests have been conducted to evaluate the plane and elevation accuracy of the 3D model of the city,focusing on the analysis of the influence of the height of aerial photography and the number of control points on the accuracy of the 3D model;At the same time,the precision of the fine model of single building has been verified and analyzed.The results show that the 3D model construction method based on UAV sequence image can reach the accuracy of centimeters,which can not only meet the precision requirements of urban real-scene model construction,but also is easy to operate,flexible in data acquisition,high in timeliness,and has important and practical engineering value.(3)Studies have been carried out on the influence factors of digital surface model accuracy,such as flight height,side overlap rate,shooting tilt angle,control point density and control point layout scheme.The results show that the plane and elevation accuracy of digital surface model model based on low altitude aerial measurement of small UAV can reach 5 cm.optimum flight altitude and shooting Angle are 60 m and 45° respectively,and the recommending values of overlapping rate and control point density are 70% and 0.27 respectively;the distribution scheme of control point can be rectangular or quincunx according to the site conditions.(4)On the basis of the three-dimensional topography model building method based on tilt uav photogrammetry,the best flying scheme and model-building scheme obtained from researches have been applied in some practical projects to solve practical problems,including Tian Ma new campus buildings of Hunan university,Yun Tang campus of Changsha university of science and technology,Wenzhou Oufei engineering reclamation levee,Changsha Xiang river levee,etc.Results show that not only can model construction method based on UAV tilt photogrammetry be used to obtain highprecision 3D model of urban buildings and monomer buildings,meeting requirements of building three-dimensional model of digital city construction,but it can also be utilized to get a clear,high-precision digital surface model,satisfying the needs of patrol inspection and monitoring of large deformation of sensitive points or post disaster deformation of extremely large constructions like reclamation of heavy levees.Combined with the research content and results of this paper,some deficiencies of related research and the prospect of future research have been put forward from the aspects of camera calibration,data collection,image preprocessing,model construction and application,etc.