True Ortho-photo Generation from High Resolution Satellite Imagery

Ortho-photos provide valuable spatial and spectral information for various GIS and mapping applications. The absence of relief displacement and the uniform scale in ortho-photos enable interested users to measure distances, compute areas, derive geographic locations, and quantify changes. Differential rectification has traditionally been used for ortho-photo generation. However, differential rectification produces serious problems (in the form of ghost images) when dealing with large scale imagery over urban areas. To avoid these artifacts, true ortho-photo generation techniques have been devised to remove ghost images through visibility analysis and occlusion detection. So far, the z-buffer method has been one of the most popular methods for true ortho-photo generation. However, it has strict requirements regarding the cell size of the Digital Surface Model (DSM), as the cell size is related to the Ground Sampling Distance (GSD) of the imaging sensor. This paper introduces alternative methodologies for true ortho-photo generation that circumvent the drawbacks of the z-buffer technique. Moreover, the proposed techniques are specially suited for manipulating scenes acquired by high resolution imaging satellites. Specifically, the proposed methodologies focus on object to image projection and occlusion detection when dealing with line cameras. Using real data, the experimental results section describes a comprehensive analysis of the performance of the proposed methodologies when compared to existing techniques. The analysis focuses on the quality of detected occlusions and the computational efficiency.