Peter DORNINGER / Clemens NOTHEGGER
(Vienna University of Technology, Christian Doppler Laboratory for “Spatial Data from Laser Scanning and Remote Sensing, Vienna, Austria)
Terrestrial Laserscanning has proved to be an important tool for documentation of cultural heritage objects. The latest generation of phase shift scanners features an extremely high scanning speed and improved accuracy, thus making it possible to capture surface detail in the millimeter range. This was previously the exclusive domain of close range triangulation scanners. These scanners, however, usually have a very limited field of view, thus requiring a large number of scans even for relatively small objects. This can be economically prohibitive. Phase shift scanners, on the other hand, produce huge amounts of data, which commonly used modeling software cannot handle properly.
We developed a workflow comprising data acquisition, point cloud pre-processing and finally model generation. The pre-processing step aims at reducing point density and measurement noise considerably while preserving richness in detail as best as possible. It is designed to be applied automatically in order to cope with the huge amount of data provided by phase shift scanners supporting measurement rates of up to one million points per second. The number of necessary control parameters is reduced to a minimum and they can be estimated automatically – a major advantage over commercial software.
To prove the stated hypothesis of modeling at millimeter accuracy, we applied the proposed workflow on a tile stove, decorated with Rocaille ornaments. The stove is part of the “White-gold-rooms” of the UNESCO World Heritage Site Schönbrunn Palace. It was scanned before the restoration. Afterwards, it was completely dismantled into peaces with a maximum size of 50 by 50 centimeter. After rebuilding the object, it was scanned a second time.
Within our contribution, we outline the main characteristics of the proposed point cloud pre-processing step. Afterwards, we demonstrate that the pre-processed scans allow for deformation documentation at millimeter range. Hence, the comparison of the two models, acquired before and after the restoration, allows for analyzing surface differences at millimeter scale.
Keywords: Laser Scanner, Accuracy, Deformation Analysis, Cultural Heritage