Abstract
Abstract. Usually aerial imagery are acquired through perspective projection which results in relief displacement in the map. Therefore, orthophotos from large scale aerial images over urban area often suffer from double mappings caused by sudden elevation changes in the scene. In the generation of true orthophotos, one aims at removing these perspective displacements and occlusions. Hence, knowledge of the surface shape is needed, as it has great impacts both on the orthorectification and occlusion identification. Mostly, the relief displacements are caused by buildings. In this paper, we present a method for the generation of true orthophotos from overlapping aerial images of known orientation, especially in built-up areas. Apart from the aerial images, the method does not depend on additional data sources. In particular, we focus on the derivation of building roof outline model using image segmentation and edge detection techniques under the guide of the classification result of point cloud from image matching . Experiment results on real data show the feasibility and the performance of the method.
Highlights
Aerial images are subject to perspective distortion and cannot be used directly as a map with homogeneous scale
Usually aerial imagery are acquired through perspective projection which results in relief displacement in the map
Orthophotos from large scale aerial images over urban area often suffer from double mappings caused by sudden elevation changes in the scene
Summary
Aerial images are subject to perspective distortion and cannot be used directly as a map with homogeneous scale. The traditional digital orthorectification works well as there is no rapid elevation change. For large scale imagery of urban areas with complex buildings, the distortion produces unavoidable artifacts in the form of double mapped areas, reduces the usefulness and reliability of the orthomap. The term true orthophoto is generally used for an orthophoto where surface elements that are not included in the digital terrain model are rectified to the orthogonal projection (Amhar et al, 1998). For generation of a true orthophoto two aspects need to be considered. If the image ray has more than one intersection with the objects, including the terrain, resulting in hidden areas and double mapping
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