Research On Making Digital Orthophoto Map Based On Position And Orientation System

Aerial photogrammetry is the main method of datas acquisition in land reso-urce,whose mission is making digital orthophoto map(DOM).Traditional aerial photogrammetry has complicated process and long production cycle due to the requirement of ground control points.It can not update geographical datas in time.In view of the above problems,the POS technology provides an effective solution.The main idea of POS technology is to combine position and orientation system with unmanned aerial vehicles,and perform direct georeferencing.This technology has great practical significance to break the limitation of ground control points.However,the DOM is difficult to meet the requirements of surveying precision.So it is impossible to judge the true information of DOM accurately.Based on the above backgrounds.In this paper,a method of making DOM production is studied without ground control points,which is based on the operation mode of POS and UAV remote sensing integration.The main research contents and conclusions are as follows:The correction of image distortion takes two steps.The first is to establish the mapping relationship between distorted image and undistorted images.The second is to resample for eliminating the distortion of image caused by camera lens distortion.The POS datas is calibrated by the geometric rotation relationship.In this way,POS datas is calibrated as the real exterior elements of image.The advantages and disadvantages of classical geometric correction algorithms are analyzed.In order to solve the problem of pixel unevenness caused by positive solution,and the defect that inverse solution cannot get the image coverage.In this paper,the geometric correction algorithms based on collinear condition equation is improved.Firstly,the ground coordinates of the four vertices of the image are calculated by positive solution to get the image coverage.Then the image was corrected by inverse solution.The results show that the accuracy of corrected DOMs meet the requirements of photogrammetric mapping specification.At the same time,the calculation time can be reduced and the operation efficiency can be improved.Study on basic principle about network adjustment is made.In order to improve the accuracy of DOM under the condition of no ground control points,the algorithm of free network adjustment based on virtual control points is improved.DOM can be made without control points by improving the method of generating virtual control points and building adjustment model.First,the improved adjustment algorithm was used to test the original datas.Then the DOM results are analyzed with the median error index.The results show that the algorithm is effective.Finally,the improved geometric correction method is used to correct the images of Fo Shan area.The DOM obtained satisfies the requirements that the error of feature points is no more than 0.6m under large scale mapping of 1:1000.Then comparison is made between Terra photo's and the results optimized,which indicates the improved adjustment algorithm is feasible.