FOR 5455:  Deformation analysis based on terrestrial laser scanner measurements (TLS-Defo)

• Subject Area: Geosciences
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 490989047

Within geodetic deformation analyses, congruency investigations statistically test geometric changes of two or more object states. A rigorous assessment of significance is needed to separate between geometric changes and the uncertainty of measurements and data processing methods. Within the current state of the art, the deformation analysis rests upon point-based measurements, acquired by e.g. total stations, GNSS or extensometers. The preselection of these individual points, that should characterize the object, falls into the responsibility of the engineer. In general, this selection demands interdisciplinary collaboration. After analyzing the movement of these individual points, the movement of the complete object is gained by a spatial generalization process. The terrestrial laser scanning (TLS) is already an established method for reality capture. For rigorous deformation analyses, it has been used only rarely so far. The great advantage of TLS-based deformation analyses is that the object is sampled with a high spatial resolution of the resulting point cloud. Thus, the subjective object discretization with individual points can be omitted, leading to more objective analyses. Nevertheless, in order to use TLS for deformation analyses, several challenges need to be solved. These challenges are closely related to the previously mentioned demand on small measurement uncertainties and strict significance investigations that need an entirely determined uncertainty budget. The challenges are: • A surface representation of the measured object surface is needed that allows for representing object details as well as for introducing smoothness assumptions. Additionally, changes in individual parameters should be connectable to individual –if possible spatially limited– deformations. • Calibrating the laser scanner so that systematic instrumental errors are minimized. • Determining a realistic covariance matrix of the TLS measurements. • Quantifying the model uncertainty that originates from deviations in the surface representation of the measured object surface since this representation only approximates the real surface. • Complement the stochastic model of TLS measurements and model uncertainty by concepts for distribution-free uncertainty modelling to take remaining systematic errors into account by sets and intervals. • Segmentation of deformed and non-deformed parts of the point cloud and robust determination of the geodetic datum for the laser scans to accurately transform different laser scans in a consistent coordinate frame. • Analyzing the sensitivity of the deformation analysis to determine optimal measurement geometries and scanner settings so that deformations can be detected as early and as reliably as possible. This proposed research unit aims at solving these challenges to make a substantial contribution to using TLS for deformation analyses. The gained findings will be transferable to other area-based measurement techniques.

• DFG Programme: Research Units
• International Connection: Austria

Projects

• Calibration of Laser Scanners (Applicant Kuhlmann, Heiner )
• Coordination Funds (Applicant Kuhlmann, Heiner )
• Distribution-free Uncertainty Description for TLS-based Areal Deformation Analysis (Applicant Schön, Steffen )
• Measurement Uncertainty: Determining generalized variance-covariance matrices of terrestrial laser scans considering all relevant error sources (Applicant Holst, Christoph )
• Surface approximation uncertainty (Applicant Neumann, Ingo )
• Surface Representation and Area-wise Deformation Analysis (Applicant Harmening, Corinna )

• Spokesperson: Professor Dr.-Ing. Heiner Kuhlmann