Urban Image True Orthorectification in The National Map Program

The large-scale urba n orthoimage generation is being deployed in all level government agencies and private sectors. However, the early procedures and algorithms for digital orthoimage generation in the National Digital Orthophoto Program (NDOP) were based on earlier USGS mapping operations, which have not considered the urban case so that the Standard for Digital Orthophoto formulated by USGS has not considered the requirements of large-scale city orthophoto generation. To provide advanced technical basis (algorithms and procedures) and experience needed for national large -scale digital orthophoto generation and the revision of the Standards for National Large-scale City Digital Orthophoto in National Digital Orthophoto Program (NDOP), this paper presents a comprehensive study on theories, algorithms, and methods of large -scale urban orthoimage generation. These techniques include DTM-based orthoimage generation, DBM-based orthoimage generation, and their mergence for true orthoimage generation, the problems of orthoimage generated using traditional method, building occlusions and compensation, the data structure to model urban buildings for accurately generating urban orthoimage, shadow detection and removal, the optimization of seamline for automatic mosaic, and radiometric balance of neighbor images, street visibility analysis.