Search

[EN] Multispectral imaging (MSI) is increasingly used for the documentation and analysis of cultural heritage. It provides conservators a powerful non-destructive technique (NDT) and non-contact tool for detecting damage, hidden features and material-specific characteristics. Hereby multispectral documentation of wall paintings in an urban environment poses special challenges for the art expert. For example, these are often large works of art located outdoors on building façades. Excitation with artificial light in well-defined spectral ranges, as should ideally be the case in MSI, is therefore often not possible. In the following, low-cost variants of MSI (ultraviolet reflectography, visible light imaging and infrared reflectography) in combination with 3D photogrammetry and statistical methods for analysing image data are tested and discussed. Hereby, a metrically correct, large-scale documentation of wall paintings with accurate superimposed images of different spectral ranges will be generated by linking the MSI data in a photogrammetric image cluster to create individual texture maps for each spectral band. Furthermore, Principal Component Analysis (PCA) is used to extract additional information from the MSI data. The case studies are located on the campus of the Universitat Politècnica de València., This study was carried out within the project “REVIEW– REVealing hIddEn Wall paintings” and has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 101032333

The initial focus of this research was on the development of a general workflow for the documentation and monitoring of historical stained glass windows using structured light scanning. Therefore windows from different churches, time periods and with different corrosion and damage phenomena were scanned before and after conservation measures. To evaluate the execution of the restoration measures the data was compared using 3D inspection software to examine the differences in geometry between the two scans. Various problems had to be solved, for example, how to deal with heavily reflective surfaces and the extreme contrast between light and dark surfaces, as seen in the borders between ‘Schwarzlot’ painting and plain glass. The application of materials for matting the surfaces, such as Cyclododecane spray, was impossible due to the high accuracy of the surface measurement required for 3D inspection. Regarding the contrast differences of the surfaces, the creation of exposure fusions and the use of polarization filters to reduce reflections were tested. In addition to the general problems encountered when recording translucent surfaces, the historical glasses caused additional problems in calculating surface comparisons. For example, the windows have to be moved and turned around several times, both during the conservation process and while scanning, causing deformations of the geometry due to the flexible lead rods allowing a certain degree of movement.

Monitoring is an essential requirement for the planning, assessment and evaluation of conservation measures. It should be based on a standardized and reproducible observation of the historical surface. For many areas and materials suitable methods for long-term monitoring already exist. But hardly any non-destructive testing methods have been used to test new materials for conservation of damaged stone surfaces. The Nano-Cathedral project, funded by the European Union's Horizon 2020 research and innovation program, is developing new materials and technologies for preserving damaged stone surfaces of built heritage. The prototypes developed are adjusted to the needs and problems of a total of six major cultural monuments in Europe. In addition to the testing of the materials under controlled laboratory conditions, the products have been applied to trial areas on the original stone surfaces. For a location-independent standardized assessment of surface changes of the entire trial areas a monitoring method based on opto-technical, non-contact and non-destructive testing methods has been developed. This method involves a three-dimensional measurement of the surface topography using Structured-Light-Scanning and the analysis of the surfaces in different light ranges using high resolution VIS photography, as well as UV-A-fluorescence photography and reflected near-field IR photography. The paper will show the workflow of this methodology, including a detailed description of the equipment used data processing and the advantages for monitoring highly valuable stone surfaces. Alongside the theoretical discussion, the results of two measuring campaigns on trial areas of the Nano-Cathedral project will be shown.

Berichte des KDWT, 1, 90-91

The article deals with the comparison between 2D and 3D evaluation of surface areas of sculptures. The objects chosen for investigation were Apollo (Carrara Marble, Potsdam Sanssouci), Flora (Laas Marble, Castle and Park Nymphenburg Munich) and Juno (Cotta Sandstone, Baroque Garden Grossedlitz/Dresden). Photographs showing the sculptures from all sides were used for calculating 2D surface areas with AutoCAD 2018 software. 3D models were generated with T-Scan 2 (Steinbichler Company), and 3D surface areas were evaluated with CAD software Geomagic Studio. The results show that 3D total surface area determinations of virtual 3D models are much more precise than 2D determinations on photographs. The values of the total surface area differ significantly. In case of Apollo 2D measurement captures only 66% of the real total surface. For measuring surface roughness, standardized Bosch sandpapers with P classification were used. Microphotographs of marble and sandstone surfaces show the development and the general optical appearance of increasing roughness. As expected, 2D calculation gives smaller values than 3D calculation also in case of surface roughness. In case of Apollo the P400 roughness area calculated with 2D measurement yields only 26% of the real area calculated with 3D. The accuracy of the surface 2D measurement clearly depends on the complexity of the sculpture because undercuts cannot be captured on photographs. It is shown that accurate information about the distribution of damage phenomena helps to improve planning conservation measures.

Sri Dalada Maligawa – the Temple of the Sacred Tooth Relic – is one of the most important pilgrim sites in Buddhist culture. It is the main part of the UNESCO World Heritage Site Sacred City of Kandy. Since the end of the 17th century the temple has been keeping the sacred tooth of the Buddha. Until now an accurate documentation of the temple with all its rich decorations is missing. The Temple is built in an area vulnerable to environmental factors like earthquakes or monsoon rains and was the target of terrorist attacks. To help preserving this important cultural heritage a research project was carried out. Main part of the project was a 3D-documentation of the entire temple by using Terrestrial-Laser-Scanning (TLS) and the creating of CAD-Plans. In addition to the documentation of the architecture several details were taken in high resolution by Structured-Light-Scanning (SLS). All data will be part of the digital archive of the temple and were used as a base for a general site monitoring, especially to observe cracks. Next to the mere documentation a transfer of knowledge was another aim of the project. In future most of the analysis of the scan data can be done by local specialists.

The Igel Column, 23 m high, is one of the best known Roman column monuments in Germany and is part of the UNESCO World Heritage `Roman Structures, Cathedral and Church of Our Lady' in Trier. The list also includes a faithfully reconstructed and colored one-to-one copy of the column monument from the early 20th century, which is located at the Rheinisches Landesmuseum Trier. Both original and copy are in danger of decay and require comprehensive restoration. Commissioned by the LBB Trier, ArcTron3D GmbH documented both monuments with combined terrestrial and airborne high-resolution 3D scanning technologies. Apart from terrestrial laser scanning and structured light scanning, SFMphotogrammetry was carried out from a lifting platform and a camera copter (MAV - Micro Aerial Vehicle). The data fusion and processing resulted in photorealistic high-resolution 3D models. These models were managed and prepared in ArcTron3D's database-supported 3D information system aSPECT3D, which is able to handle large data amounts. For further use during the restoration process, the database allows systematic access to all project data, which was structured according to archaeological and restoration questions.

Berichte des KDWT, 1, 92-95

Der Einsatz von berührungslosen, dreidimensionalen Vermessungsgeräten hat sich in den letzten 10 bis 15 Jahren mehr und mehr in der Kulturerbeforschung etabliert. Unter dem schützenden Feigenblatt des Verweises auf die Verwendung neuer Techniken, deren eingehende Erprobung noch aussteht, wurde dabei jedoch häufig auf die Einhaltung gängiger ethischer Grundlagen und damit dem Ziel eines tatsächlichen Mehrwerts für das Kulturerbe verzichtet. Dies mag für die Anfänge der Verwendung einer zerstörungsfreien Technologie hinnehmbar sein, doch werden damit zusehends das Potential und der Mehrwert des gezielten Einsatzes dieser Technologien verunklärt. Es droht die Gefahr, ein nützliches Werkzeug lediglich als Spielerei zum Selbstzweck oder für reißerische Visualisierungen abzustempeln. In der hier vorliegenden Arbeit soll daher der Mehrwert und praktische Nutzen neuer Technologien für den analytischen Einsatz in der Kulturerbeforschung, als Werkzeug für die Untersuchung und Dokumentation von materiellem Kulturerbe herausgearbeitet und klar dargestellt werden. Der Schwerpunkt liegt dabei in dem Einsatz von bildgebenden, berührungslosen und zerstörungsfreien optischen Messtechniken. Konkret werden hierbei verschiedene Methoden zur dreidimensionalen Erfassung von komplexen Oberflächen ganzer Bauwerke bis hin zu kleinsten Oberflächenmerkmalen im Submillimeterbereich sowie die multispektrale Bildgebung behandelt. Neben der Darstellung von Möglichkeiten und Limitationen bei der Erhebung der Daten, beispielsweise aufgrund der im Kulturgut verwendeten Materialien, werden verschiedene Verfahren zur Auswertung der Daten dargestellt. Einen besonderen Schwerpunkt wird dabei die Anwendung von 3D-Inspektionssoftware zum Vergleich von 3D-Modellen darstellen. Hierbei handelt es sich um ein Werkzeug welches bisher kaum Anwendung in der Kulturerbeforschung fand, jedoch besonders für das Erfassen von Veränderungen eines Objektes zwischen zeitlich versetzten Digitalisierungen geeignet ist. Wie in der Arbeit dargestellt wird, ergeben sich hierdurch Möglichkeiten zur Detektion von Schadensprozessen, gleichermaßen wie die Evaluation von Konservierungsmitteln und der kunstwissenschaftliche Vergleich von in Serie produzierten Kunstobjekten. Ausgangspunkt für die in der Arbeit vorgestellten Arbeitsweisen und Anwendungen der Methoden stellt dabei stets eine konkrete Fragestellung ausgehend vom Objekt dar, nach welcher die jeweilige Technik ausgewählt und gezielt angewendet wurde. Besonders ist dabei der kombinierte Einsatz verschiedener Techniken wie etwa der 3D-Oberflächendokumentation und der multispektralen Bildgebung herauszustellen, wodurch sich Einschränkungen einzelner Methoden kompensieren und so ein Mehrwert in der Untersuchung der Kulturgüter herausarbeiten lässt. So konnte der Nutzen dieser Technologien als Werkzeuge für die Kulturerbeforschung und besonders der Präventiven Konservierung herausgearbeitet werden. Die behandelten Schwerpunkte umfassen dabei die berührungslose Dokumentation von Objekten für eine denkmalgerechte Zu- und Bestandserfassung, innerhalb der Kulturerbeforschung eine fächerübergreifende Analyse und Observation sowie das Monitoring von Kulturerbe und die langfristige Speicherung und Archivierung der erhobenen Daten. In Ermangelung ethischer Grundsätze für das große Feld der Kulturerbeforschung und an passenden Richtlinien für eine denkmalgerechte, digitale Dokumentation, werden in dieser Arbeit zudem ethische Leitsätze für die Kulturerbeforschung, unter Anlehnung an die etablierten Vorgaben und Empfehlungen innerhalb der Konservierung und Restaurierung, formuliert. Diese Leitsätze sind dabei als Vorschlag für die Wahrung eines denkmalgerechten Umgangs mit dem Objekt durch alle beteiligten Disziplinen und Akteur*innen zu sehen. Durch sie soll die Notwendigkeit und der Bedarf der Definition solcher Richtlinien herausgestellt werden. Sie dienen dabei als Appell an internationale Institutionen wie etwa ICOMOS, ICOM und ICCROM dem Desiderat fehlender, vereinfachter ethischer Leitsätze für Fachdisziplinen, welche nur zeitweise in der Kulturerbforschung involviert sind, entgegenzuwirken.

Berichte des KDWT, 1, 100-102

Berichte des KDWT, 1, 98-99