Comprehensive Analysis of Alternative Methodologies for True Orthophoto Generation from High Resolution Satellite and Aerial Imagery

Orthophotos provide valuable spatial and spectral information for various GIS and mapping applications. The absence of relief displacement and the uniform scale in orthophotos enable interested users to measure distances, compute areas, derive geographic locations, and quantify changes. Differential rectification has traditionally been used for orthophoto 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 orthophoto 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 orthophoto 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 orthophoto generation that circumvent the drawbacks of the z-buffer technique. Moreover, the proposed techniques are suited for manipulating scenes acquired by both high resolution imaging satellites and aerial imaging system. Specifically, the proposed methodologies focus on object to image projection and occlusion detection. 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. * Corresponding author.