CARTOMETRIC ANALYSIS AND DIGITAL ARCHIVING OF HISTORICAL SOLID TERRAIN MODELS USING NON-CONTACT 3D DIGITIZING AND VISUALIZATION TECHNIQUES.

摘要

This paper presents a new methodology for assessing the accuracy of historical solid terrain models using non-contact 3D digitizing techniques and demonstrates new possibilities for providing a digital archive of such precious artefacts of our cultural heritage. The famous models of the Swiss modeller Joachim Eugen Muller (1752-1833) and models created by the Allies during the Second World War have been scanned using a Minolta VI-900 laser scanner which is a high resolution, high accuracy 3D scanner that uses laser triangulation to measure distances to points. Comparison with current digital elevation data using trend surface analysis has enabled us to assess the accuracy of these models. 3D non-contact digi tizing has proved itself to be highly suited to this type of research. It is fast, flexible and accurate. However, we are now in a position to suggest improvements in the way that it is operated in future. During the initial scanning it was not easy to gauge the success of each scan using the scanner's built-in viewer, and issues with the scans only became apparent during post-processing. The texture capture proved to be especially difficult, as the necessary lighting condition for the laser scan did not lend itself for the capture of the image information. This, combined with the relatively low resolution of 640×480, meant that the images were low resolution and poorly exposed. A seconda ry image capture using better lighting and a better image sensor, such as a calibrated digital SLR, and subsequent image registration to the finished 3D model would be our preferred method in future. The results of the models scanned so far sugge st that solid terrain models were made primarily to establish the three dimensional structure of the landscape with the emphasis on providing a depiction of the landscape as a continuously changing surface. Absolute altitudes and relative heights were perhaps of secondary importance to the more important problem of filling the gaps between known measured points and providing a human view of the landscape. The results provide objective testimony to the skill and endeavour of the model makers using prim itive techniques by modern standards. The results also demonstrate that non-contact 3D digitizing techniques not only provide a suitable data capture method for solid terrain model analysis, but also provide a means of preserving digital facsimiles of su ch precious artefacts in the future.