Use of Photogrammetry and Terrestrial Laser Scanning to Measure Superficial Weathering Damage on the Façade of Hanfelden Castle, Austria

Abstract

Hanfelden Castle is one of the few Renaissance castles in Austria, which were subsequently hardly redesigned and changed since the tower building from the 14^th century, and the extension in the 16^th century to the today's appearance. This includes the façade with plaster layers from the 16^th to the 18^th century on the south and west side. Under these conditions, the concept for future scientific research of the object should essentially cover two needs: On the one hand, a collection of 3D basic data as complete as possible should be created for further work with the help of geospatial-technological methods, and on the other hand, methodological-technical expertise should also be built up (no substantial investigations have been undertaken in this direction). Additionally, and with regard to the determination of mostly conservation measures- the façade should be preserved - it has been important to check the façade made of plaster, natural stone or brick for the extent of superficial damage - such as weathering, flaking, bulging or bending. Therefore, non-contact 3D measuring systems are compared and applied as an alternative to visual inspection using standard cherry pickers or scaffolding. These so-called geospatial technologies applied in this study include methodological aspects of terrestrial photogrammetry, UAV assisted photogrammetry, and terrestrial laser scanning (TLS). This study used historical data/recordings and photogrammetric results from 1986 as well as newer techniques from the structure from motion (SfM) method (2019, 2022) and terrestrial laser scanning (2019, 2022). The different data recording methods and different result data in a multi-temporal and multi-sensoral approach, comparable for the changes to the facade, were a challenge for the study. Despite the different methodological approaches of the technologies used, the overarching goals of the study were, on the one hand, to detect and map the damage to the facade that has become increasingly apparent over the years. On the other hand, it has been shown that the applied 3D methods used (individually or in combination) represent a time-saving and cost-effective alternative to visual examinations using lifting platforms. The data sets obtained in the campaigns described should be homogenized and summarized in the sense of a historical BIM and serve as a basis for further work on the object. The focus was on multi- and interdisciplinarity as well as on taking into account the needs of science to science and science to public dissemination.