The Research On Fast And High Accuracy Georeferencing Methods For 3D Laser Scanning

Surface morphology and details of a complete object or scene description by using terrestrial LIDAR systems usually requires multiple scans from different stations to ensure the integrity of the data and the full expression of the morphological characteristics of objects.However,the coordinate system of each station is the inner coordinate system(IRCS,Intrinsic Reference Coordinate System of the scanner),which means that the coordinate system of each station is independent.Position and orientation of point cloud is to transform point cloud from the scanner's intrinsic reference system to the external ground reference coordinate system(GRCS),that is called,point cloud georeferencing.Traditional TLS point cloud georeferencing need a large number of standard control points or the scanners integrated position and orientation device(such as GNSS,compass),it's cost time and effort.Orientation by backsight target method is simple and fast,but only suitable for precise leveling and centering scanners.In this paper,the foundational theory and method of fast orientation were studied,aim to improve the efficiency of scanning measurement under the condition of ensuring accuracy.Two kinds of new georeferencing methods were proposed,only need a small number of standard control points(its ground reference coordinates have been identified),and then with the aid of point,line,plane features of objects to achieve point cloud coordinates georeferencing.The main research of this paper is as follows:(1)Give a comprehensive presentation of existing registration and georeferencing techniques and theory that have been applied,and introduce the georeferencing approaches of this paper.(2)Research on the georeferencing approach and mathematical model of two control points with a vertical line.This method using two control points and a vertical ridge of building on the scanning area georeferencing point cloud,vertical line method for short.The advantages are: simplify operational tasks,concise mathematical model,the orientation error of each station is independent and non-pollution.Its precision depends on the degree of roughness on the surface of the building and the degree of vertical of building ridge.(3)Research on the georeferencing approach and mathematical model of parameter transfer method.This method is in the case of core station has georeferenced,for the rest of station,first using building vertical ridge to leveling the point cloud,and then using the extracted point and line feature transfer orientation parameters,parameter transfer method for short.The advantages are: only a few stations(the core station)need to set control points,concise mathematical model,to further reduce the surveying time and to simplify operational tasks compared with the traditional method and the first approach proposed in this paper.The accuracy is also dependent on the roughness of the buildings surface and ridge verticality,because the cumulative error propagation,every 3 stations need to set new core station.(4)Indoor and outdoor experiments based on vertical line method.Generally,man-made constructions are rich in geometrical features.C hoose the school teaching building as the research object for outdoor measurement inspection the application effect of vertical line method,selected a lab to test the indoor application effect.The experimental results show that the accuracy of this method is within 2cm outdoor,and within 1cm indoor application.(5)Indoor and outdoor experiments based on parameter transfer method.As mentioned above,the proposed parameter transfer method was carried out indoor and outdoor experiments,the results demonstrate the accuracy is equal to the vertical line method.