Laser scanning has been recently confirming its high potential in the field of acquiring 3D data for architectural and engineering objects. The objective of this paper is to analyse the quality of the TLS data acquired for different surfaces of monumental objects, with consideration of distances and the scanning angles. Tests concerning the quality of the survey data and shapes of architectural objects, characterised by diversified curvature, structure and the uniformity of the surface, were performed. The obtained results proved that utilisation of terrestrial laser scanning techniques does not allow to achieve expected accuracy for some historical surfaces and it should be substituted by alternative, photogrammetric techniques. Therefore, the typology of constructions of historical objects is important not only for selection of the optimum technique of surveys, but also for its appropriate utilisation.
The test objects were architectural details of the Main Hall of the Warsaw University of Technology. Scans were acquired using the 5006h scanner. Diversified geometry of scans was tested, and the relations between the distance and obtained accuracy were specified. In the case of numerous conservational works the precise surface reconstruction is often important, in order to specify damages. Therefore, the repeatability of obtained TLS results for selected surfaces was also tested. Different surfaces were analysed, which are composed of different materials having glittery elements and inhomogeneous structure. The obtained results and performed analyses revealed the high imperfections of the TLS technique applied for measuring surfaces of historical objects. The presented accuracy of measurements of projection of historical surfaces, obtained using the TLS technique may be applied by art conservators, museum professionals, archaeologists and other specialists, to perform wide analyses of historical heritage objects.
The terrestrial laser scanning is commonly used in different areas, inter alia in modelling architectural objects. One of the most important part of TLS data processing is scans registration. It significantly affects the accuracy of generation of high resolution photogrammetric documentation. This process is time consuming, especially in case of a large number of scans. It is mostly based on an automatic detection and a semi-automatic measurement of control points placed on the object. In case of the complicated historical buildings, sometimes it is forbidden to place survey targets on an object or it may be difficult to distribute survey targets in the optimal way. Such problems encourage the search for the new methods of scan registration which enable to eliminate the step of placing survey targets on the object. In this paper the results of target-based registration method are presented The survey targets placed on the walls of historical chambers of the Museum of King Jan III's Palace at Wilanów and on the walls of ruins of the Bishops Castle in Iłża were used for scan orientation. Several variants of orientation were performed, taking into account different placement and different number of survey marks. Afterwards, during next research works, raster images were generated from scans and the SIFT and SURF algorithms for image processing were used to automatically search for corresponding natural points. The case of utilisation of automatically identified points for TLS data orientation was analysed. The results of both methods for TLS data registration were summarized and presented in numerical and graphical forms.
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