Analysis and the Solutions for Generating a True Digital Ortho Photo in Close Range Photogrammetry

Digital orthophoto is an image where the relief displacements and the camera's tilt have been removed. So it is an efficient, inexpensive and accurate approach for purposes such as evaluation, analysis or measurement of the objects presented in the images. For this reason digital orthophoto has occupied an important place in spatial database in GIS. The traditional orthophoto is based on Digital terrain model and it does not include the man-made objects. Therefore, the orthophotos of urban areas do not have satisfactory accuracy. True orthophoto generation by using the digital surface model in rectification process and detecting occluded areas through the visibility analysis is the only solution. True orthophoto can be produced from close range as well as aerial and satellite images. In this paper, to simplify the true orthophoto generation process several close range images of a cubic object are used with a regularly spaced grid DSM. In close range Photogrammetry the distance between camera and object is small and as a result the occluded areas are extensive. Therefore, the occluded areas detection method must be efficient. In this research work the height-based raytracing method is used to detect the occluded areas. To restore the information of the occluded areas the seamless automatic mosaicking considering histogram equalization of images is applied.