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A BIRD ’ S EYE VIEW ON SWITZERLAND IN THE 18 TH CENTURY : 3 D RECORDING AND ANALYSIS OF A HISTORICAL RELIEF MODEL

The relief of Franz Ludwig Pfyffer, constructed between 1762 and 1786, is considered the world’s oldest large landscape model and a pioneering work of Swiss cartography. Based on Pfyffer’s own measurements, the 6.6 x 3.9 m big masterpiece represents a fascinating bird’s eye view of the Alps. The relief is not only an extraordinary topographic but also a cultural achievement: It has once been an attraction for numerous representatives of European social and scientific life. This paper reports about the procedures for the digital recording and quantitative evaluation of the Pfyffer’s relief, which are part of a broad interdisciplinary research. For the first time, the results of the photogrammetric 3D reconstruction and accuracy analysis of the whole object are presented. The DTM, the orthoimage and the complete vector data set were archived for the documentation of the cultural heritage. For the reason of project publicity, the derivation of high quality visualization products such as flyovers and interactive models was an important issue, too. In the second part the paper describes methods for the comparison of the virtual historical model with current map information. The procedures are based on a 9-parameter transformation of identical points between two three-dimensional datasets. In particular, a new procedure for the transformation of historical height and image data has been developed and evaluated. Furthermore, a novel method for analysis of the lake contours accuracy in the old relief or in the old map respectively is suggested. The procedures enable visualization of relief distortions (including a distortion grid), overlays with current vector data as well as direct comparison of the digital terrain models. The results of the analysis bring new surprising information concerning geometric accuracy, metric parameters and building strategy of the Pfyffer’s relief.