Reconstruction of a Medieval Wall: Photogrammetric Mapping and Quality Analysis by Terrestrial Laser Scanning

摘要

Photogrammetric mapping is an important tool for the documentation of cultural heritage for renovation. Especially when a renovation involves the disassembling and later identical reassembling of a structure, it is important to determine the position and orientation of all elements within the measured objects, like the stones in a wall. High resolution photogrammetric documents make it possible to rebuild a structure as it was before the disassembling. In this article, the generation of an orthophotoplan and a 3D model, based on terrestrial photogrammetry will be discussed. Based on an overview of possible error sources in photogrammetric 3D modeling, the calculated geometric model is compared with a reference point set, acquired by terrestrial laser scanning to evaluate the quality of this model. Although terrestrial laser scanning itself does not generate a radiometric image of the object, it is very useful for the geometric reconstruction of the measured object and thus to measure the quality of geometrical photogrammetric products. A phase-based Leica HDS 6100 laser scanner is used to generate this reference point set on which the photogrammetric model is projected. The statistic error model of the final photogrammetric product enables the calculation of overall displacements and local deviations.