06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access An elementary error model for terrestrial laser scanning(2023) Kerekes, Gabriel; Schwieger, Volker (Prof. Dr.-Ing. habil. Dr. h.c.)Terrestrial Laser Scanning (TLS) is a recent method in engineering geodesy area-wise deformation analysis. After a TLS scan, the result for each epoch is a point cloud that describes the object’s geometry. For each point cloud, the stochastic properties are important for a reliable decision concerning the current object geometry. Generally, the stochastic properties are described by a stochastic model. Currently, stochastic models for TLS observations are highly disputed and incomplete. A realistic stochastic model is necessary for typical applications like structural deformation analysis for buildings and civil engineering constructions. This work presents a method to define a stochastic model in form of a synthetic variance-covariance matrix (SVCM) for TLS observations. It relies on the elementary error theory defined by Bessel and Hagen at the beginning of the 19th century and adapted for geodetic observations by Pelzer and Schwieger at the end of the 20th century. According to this theory, different types of errors that affect TLS measurements are classified into three groups: non-correlating, functional correlating, and stochastic correlating errors. For each group, different types of errors are studied based on the error sources that affect TLS observations. These types are classified as instrument-specific errors, environment-related errors, and object surface-related errors. Regarding instrument errors, calibration models for high-end laser scanners are studied. For the propagation medium of TLS observations, the effects of air temperature, air pressure and vertical temperature gradient on TLS distances and vertical angles are studied. An approach based on time series theory is used for extracting the spatial correlations between observation lines. For the object’s surface properties, the effect of surface roughness and reflectivity on the distance measurement is considered. Both parameters affect the variances and covariances in the stochastic model. For each of the error types, examples based on own research or literature are given. After establishing the model, four different study cases are used to exemplify the utility of a fully populated SVCM. The scenarios include real objects measured under laboratory and field conditions and simulated objects. The first example outlines the results from the SVCM based on a simulated wall with an analysis of the variance and covariance contribution. In the second study case, the role of the SVCM in a sphere adjustment is highlighted. A third study case presents a deformation analysis of a wooden tower. Finally, the fourth example shows how to derive an optimal TLS station point based on the SVCM trace. All in all, this thesis brings a contribution by defining a new stochastic model based on the elementary error theory in the form a SVCM for TLS measurements. It may be used for purposes such as analysis of error magnitude on scanned objects, adjustment of surfaces, or finding an optimal TLS station point position with regard to predefined criteria.