Modeling terrestrial laser scanner data for precise structural deformation measurement

A modeling strategy has been developed that permits coarse-precision terrestrial laser scanner observations to be used to accurately measure vertical deflections of deforming beams. The model is developed from fundamental beam-deflection equations and implemented using a weighted-constraint, least-squares curve-fitting approach. After the solution is computed, a statistical testing procedure is applied to assess the level of contribution of each of the estimated parameters in the model and identify redundant terms for removal. Two terrestrial laser scanners (TLSs) are employed to test the approach by measuring the vertical displacement of beams undergoing controlled loading for which the magnitude of displacements was at the 2-50 mm level. Results demonstrate that the modeled TLS data, when compared to conventional monitoring equipment, such as convergent digital photogrammetry and contact sensors, achieved an accuracy that is up to 20 times higher than the TLS's coordinate precision, thus underscoring the benefits of modeling raw point data for precise surface representation. It is shown that one brand of TLS (coordinate precision of 6 mm) reliably measured the vertical displacements with an accuracy of +/- 0.29 turn (both 1 sigma).