A new approach for relative orientation of non-calibrated historical photos of Baalbek/Libanon

Within this paper the combination of the different classes of Baalbek's historical photos for the documentation of heritage sites is discussed. We propose an effective approach in order to perform this combination which is based on an optimal orientation of the photos and the calibration of the different cameras which were used. The photos of Baalbek have poor properties (such as: different cameras used and no primary data of the cameras' parameters, different image scales, different altitudes of the flight, the contrast of the gray values and the image noise are relative great, in addition the images were taken in different dates). The posed problem in this work is: it is not a priori clear by which combination and order of the images orientation process the optimal results could be produced. Therefore, different steps of the combination between the images were investigated (e.g. orientation of vertical and oblique images together, orientation of all images etc.). Additionally, the camera calibration was achieved using the bundle block adjustment method. The computation flow in the bundle block adjustment consists of four phases. First consistency and plausibility check of input data is performed. In the second step the functional model of the calculation is derived from the collinearity equations and changed in that way that it converges well. In the third and the last phases an optimal bundle adjustment including parameters for modelling of the lens distortions is achieved. Through this method a model coordinate system was created and the errors of the image points were eliminated. As results of this work; the internal geometric configuration of the different cameras used and the lens systems were determined, furthermore the photos were oriented; so that the measurement of additional 3D points is possible, in order to use them to create a 3D City model of Baalbek which provides on one hand an important document for the city and on the other hand to understand the historical development of Baalbek's building remains from the prehistoric date until 20th century.