A New Approach for Generating a Measurable Seamless Stereo Model Based on Mosaic Orthoimage and Stereomate

Digital orthoimage (or orthophoto) is a type of information-rich digital products and has found applications in many fields. However, digital orthoimage itself is a 2-dimensional product and therefore it is insufficient for many applications. On the other hand, the traditional stereo model of photogrammetry formed from a pair of overlapping aerial photographs offer the possibility of both 3D measurement of terrain surface and terrain objects. However, it cannot be used a plan like the case of digital orthoimage and the model size is usually limited to the stereo pair. To take the advantage of both, the concept of stereomate was introduced by Collins in 1968. It is a new image with additional relief displacement. The total amount of relief displacement at each point of the stereomate is exactly the same as the sum of two relief displacements at the same position on both images of the stereo pair. That is, if this stereomate is used together with the orthoimage, one is still able to reconstruct a 3D surface of the area precisely. The main limitation with the current practice is that if more than one stereo pairs are used to generate the stereo orthophoto pair, the solution is not rigorous and thus leads to low accuracy of 3D measurement in highly mountainous areas although reasonable accuracy of 3D measurement can be achieved in areas with low relief. This paper introduces the concept of “measurable seamless stereo model”, which is formed by a mosaic orthoimage and a mosaic stereomate (i.e. mosaics of a whole block of aerial photographs), with the lineage (image coordinates on original photograph and the orientation parameters of the original photograph) of each pixel on both mosaic orthoimage and a mosaic stereomate recorded. Such a measurable seamless stereo model not only provides seamless 3D landscape environment but also offers the rigorous and thus accurate 3D measurement of any object and feature visible in the measurable seamless stereo model without explicit orientation procedure. Experimental results that the accuracy of 3D measurement from the “measurable seamless stereo model” proposed in this study is about 20 times higher than that from the traditional orthoimage pairs and is nearly similar with that in the original photo-pair model.