Deformation Measurements at Historical Buildings with Terrestrial Laserscanners

With the classical deformation measurement the objects are modeled by a number of measurement points which are distributed according to the deformation symmetrically as a grid or attached at selected principal points of movement. The measurement points can be determined with a total station (angle and distance measurements) to a high precision with a standard deviation of the 3D position of ±1...2 mm. However, these procedures have the disadvantage that only the movement of the measurement points can be determined. Movements between the measurement points, like the twisting of the object, cannot be detected this way. The interpretation is more difficult because historical buildings have a very rough surface with separate coarse stones, and the forms are often complex, e.g., multi-level church towers. New measuring instruments, like laser scanners, offer the possibility of a fast and approximately complete data acquisition of the buildings. It was to be considered if it is possible to derive changes from laser scanner data at different epochs. For the investigation, different churches in Schleswig Holstein were selected as suitable deformation objects. All churches are characterized by the fact that they were built on unfavorable ground (silt and peat). The density distribution of these materials is not homogeneous and therefore there are no setting movements but tilting of the buildings. In the cathedral of Meldorf a first measurement was performed with the IMAGER 5003 of Zoller&Fröhlich, and the changes were to be observed on a continuous base.