Research On Key Tecnology Of Large-scale True Orthophoto Generation

True orthophoto production has become a new field of photogrammetry,it's a very promising direction.Different with traditional orthophoto,true orthophoto has corrected occlusion during rectification processing and the shadow exists in image,it has higher geometric precision and more abundant information.True orthophoto can make better image mosaicing,topographic maps registering and 3D landscape map generation.Based on the analysis of the distinction between traditional orthophoto and true orthophoto,this passage summed the production process of true orthophoto and got the algorithm implemented.The passage focused on two parts of true orthophoto production: occlusion detection and compensation,shadow detection and enhancement,and compared the advantages and disadvantages of different methods through experiments.The major works implemented are listed as follow:1.Described the background and current situation of true orthophoto.Analyzed the differences between true orthophotos and tradition orthophotos,and emphasized the importance of true orthophoto generation.Summarized the production flow of large-scale true orthophoto generation,and generalized the problems confronted in current research.2.Summarized the occlusion detection methods,based on digital surface model,implemented the method based on distance,the method based on angle and ray tracing method to get occlusion area.Proposed an improved method based on rasterized digital building model to detect occlusion,the method considered both the ground occlusion caused by building and the occlusion between buildings,and achieved good detection result.3.Based on occlusion detection,compensated the occlusion by using adjacent images and neighbour pixels in origin image,and recovered the true landscape in occlusion area,achieved good result.4.Studied the principal of shadow detection,shadow detection method was implemented in RGB color space and HSV space.Proposed a method which combined principal component transformation with image segmentation to detect shadow and the result was good.5.Based on shadow detection,the passage built the processing flow of shadow enhancement.Wallis filter and close region mapping method were used to enhance shadow,and the shadow information was improved well.