The Study Of Extraction Of The Tie Point In Aerial Triangulation

In the aerial photography process, because of the changes of photograph time,solar elevation angle,some ground objects and ground vegetation with certain height have different locations on different routes, and for the general texture analysis,in the process of feature extraction,These points are easily extracted, which resulted in imprecise points, reducing the accuracy of aerial triangulation.Practice proved to overcome the impact caused by the photography time, sun elevation angle, photography locations,some special feature points must be extracted and the corresponding feature matching method must be applied, which is the key for automatic aerial triangulation. In this paper, the relevant feature extraction algorithms are studied with the aim to realize the extraction and matching of the tie point in aerial triangulation .The main contents and conclusions of this paper are as follows:1.the image preprocessingWallis transformation is widely employed for image enhancement in the field of photogrammety and remote sensing. However, the original wallis transformation has the blocking effect phenomenon, which will yield many false features in image matching. In this paper, an improved wallis transformation is proposed, in which the bilinear interpolation is adopted to avoid the blocking effect. The experiment about blob extraction and image matching, using the LoG operator, demonstrates that our method is useful to increase the number of features extracted and decrease the number of false features.2.the traditional feature points extraction and matchSeveral feature extraction operators are introduced which have a wide application in photogrammetry : Moravec operator, Forstner operator, Harris operator and the SUSAN operator, the paper gives a performance through a large number of experiments,including the advantages and disadvantages and the adapted conditions.The SIFT feature matching method and the application in photogrammetry is studied, SIFT features are extracted in images reduced in size,the mismatch points are removed using the geometric constraint, and relocate the features to the original image with the pyramid-related method , the experiment proved that the method can only be used for rough location for aerial image and not fit for the aerial triangulation which need high precision.3.the extraction and matching of the tie point in aerial triangulationThe method of extraction of the tie point is proposed based on the theory of LoG,The correlation matching, single point least squares matching and relative orientation are explained;Finally, the experiments of relative orientation proved that the Blob features automatically extracted meet the requirement of relative orientation.Also,the paper give a access of the method using two arrears,and the match number and precision is good,the method help to resolve the problem.