Deformation Analysis Using B-Spline Surface with Correlated Terrestrial Laser Scanner Observations—A Bridge Under Load

The choice of an appropriate metric is mandatory to perform deformation analysis between two point clouds (PC)—the distance has to be trustworthy and, simultaneously, robust against measurement noise, which may be correlated and heteroscedastic. The Hausdorff distance (HD) or its averaged derivation (AHD) are widely used to compute local distances between two PC and are implemented in nearly all commercial software. Unfortunately, they are affected by measurement noise, particularly when correlations are present. In this contribution, we focus on terrestrial laser scanner (TLS) observations and assess the impact of neglecting correlations on the distance computation when a mathematical approximation is performed. The results of the simulations are extended to real observations from a bridge under load. Highly accurate laser tracker (LT) measurements were available for this experiment: they allow the comparison of the HD and AHD between two raw PC or between their mathematical approximations regarding reference values. Based on these results, we determine which distance is better suited in the case of heteroscedastic and correlated TLS observations for local deformation analysis. Finally, we set up a novel bootstrap testing procedure for this distance when the PC are approximated with B-spline surfaces.

Download Full-text

Choosing the optimal number of B-spline control points (Part 2: Approximation of surfaces and applications)

Journal of Applied Geodesy ◽

10.1515/jag-2016-0036 ◽

2017 ◽

Vol 11 (1) ◽

Cited By ~ 4

Author(s):

Corinna Harmening ◽

Hans Neuner

Keyword(s):

Data Analysis ◽

Laser Scanner ◽

Point Clouds ◽

Optimal Number ◽

Deformation Analysis ◽

Control Points ◽

Trial And Error ◽

B Spline ◽

B Splines ◽

Spline Surfaces

AbstractFreeform surfaces like B-splines have proven to be a suitable tool to model laser scanner point clouds and to form the basis for an areal data analysis, for example an areal deformation analysis.A variety of parameters determine the B-spline's appearance, the B-spline's complexity being mostly determined by the number of control points. Usually, this parameter type is chosen by intuitive trial-and-error-procedures.In [The present paper continues these investigations. If necessary, the methods proposed in [The application of those methods to B-spline surfaces reveals the datum problem of those surfaces, meaning that location and number of control points of two B-splines surfaces are only comparable if they are based on the same parameterization. First investigations to solve this problem are presented.

Download Full-text

Robust external calibration of terrestrial laser scanner and digital camera for structural monitoring

Journal of Applied Geodesy ◽

10.1515/jag-2018-0038 ◽

2019 ◽

Vol 13 (2) ◽

pp. 105-134 ◽

Cited By ~ 2

Author(s):

Mohammad Omidalizarandi ◽

Boris Kargoll ◽

Jens-André Paffenholz ◽

Ingo Neumann

Keyword(s):

Em Algorithm ◽

Laser Scanner ◽

Digital Camera ◽

Point Clouds ◽

Deformation Monitoring ◽

Deformation Analysis ◽

Terrestrial Laser Scanner ◽

External Calibration ◽

3D Point Clouds ◽

Calibration Parameters

Abstract In the last two decades, the integration of a terrestrial laser scanner (TLS) and digital photogrammetry, besides other sensors integration, has received considerable attention for deformation monitoring of natural or man-made structures. Typically, a TLS is used for an area-based deformation analysis. A high-resolution digital camera may be attached on top of the TLS to increase the accuracy and completeness of deformation analysis by optimally combining points or line features extracted both from three-dimensional (3D) point clouds and captured images at different epochs of time. For this purpose, the external calibration parameters between the TLS and digital camera needs to be determined precisely. The camera calibration and internal TLS calibration are commonly carried out in advance in the laboratory environments. The focus of this research is to highly accurately and robustly estimate the external calibration parameters between the fused sensors using signalised target points. The observables are the image measurements, the 3D point clouds, and the horizontal angle reading of a TLS. In addition, laser tracker observations are used for the purpose of validation. The functional models are determined based on the space resection in photogrammetry using the collinearity condition equations, the 3D Helmert transformation and the constraint equation, which are solved in a rigorous bundle adjustment procedure. Three different adjustment procedures are developed and implemented: (1) an expectation maximization (EM) algorithm to solve a Gauss-Helmert model (GHM) with grouped t-distributed random deviations, (2) a novel EM algorithm to solve a corresponding quasi-Gauss-Markov model (qGMM) with t-distributed pseudo-misclosures, and (3) a classical least-squares procedure to solve the GHM with variance components and outlier removal. The comparison of the results demonstrates the precise, reliable, accurate and robust estimation of the parameters in particular by the second and third procedures in comparison to the first one. In addition, the results show that the second procedure is computationally more efficient than the other two.

Download Full-text

Robust Spatial Approximation of Laser Scanner Point Clouds by Means of Free-form Curve Approaches in Deformation Analysis

Journal of Applied Geodesy ◽

10.1515/jag-2015-0020 ◽

2016 ◽

Vol 10 (1) ◽

Cited By ~ 15

Author(s):

Johannes Bureick ◽

Hamza Alkhatib ◽

Ingo Neumann

Keyword(s):

Laser Scanner ◽

Point Clouds ◽

Measured Data ◽

Free Form ◽

Deformation Analysis ◽

B Spline ◽

B Splines ◽

Spline Fitting ◽

Data Gaps ◽

Spatial Approximation

AbstractIn many geodetic engineering applications it is necessary to solve the problem of describing a measured data point cloud, measured, e. g. by laser scanner, by means of free-form curves or surfaces, e. g., with B-Splines as basis functions. The state of the art approaches to determine B-Splines yields results which are seriously manipulated by the occurrence of data gaps and outliers.Optimal and robust B-Spline fitting depend, however, on optimal selection of the knot vector. Hence we combine in our approach Monte-Carlo methods and the location and curvature of the measured data in order to determine the knot vector of the B-Spline in such a way that no oscillating effects at the edges of data gaps occur. We introduce an optimized approach based on computed weights by means of resampling techniques. In order to minimize the effect of outliers, we apply robust M-estimators for the estimation of control points.The above mentioned approach will be applied to a multi-sensor system based on kinematic terrestrial laserscanning in the field of rail track inspection.

Download Full-text

Fitting Terrestrial Laser Scanner Point Clouds with T-Splines: Local Refinement Strategy for Rigid Body Motion

Remote Sensing ◽

10.3390/rs13132494 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2494

Author(s):

Gaël Kermarrec ◽

Niklas Schild ◽

Jan Hartmann

Keyword(s):

Point Cloud ◽

Goodness Of Fit ◽

Laser Scanner ◽

Point Clouds ◽

Statistical Testing ◽

Computational Time ◽

Terrestrial Laser Scanner ◽

Reference Surface ◽

Local Refinement ◽

Surface Approximation

T-splines have recently been introduced to represent objects of arbitrary shapes using a smaller number of control points than the conventional non-uniform rational B-splines (NURBS) or B-spline representatizons in computer-aided design, computer graphics and reverse engineering. They are flexible in representing complex surface shapes and economic in terms of parameters as they enable local refinement. This property is a great advantage when dense, scattered and noisy point clouds are approximated using least squares fitting, such as those from a terrestrial laser scanner (TLS). Unfortunately, when it comes to assessing the goodness of fit of the surface approximation with a real dataset, only a noisy point cloud can be approximated: (i) a low root mean squared error (RMSE) can be linked with an overfitting, i.e., a fitting of the noise, and should be correspondingly avoided, and (ii) a high RMSE is synonymous with a lack of details. To address the challenge of judging the approximation, the reference surface should be entirely known: this can be solved by printing a mathematically defined T-splines reference surface in three dimensions (3D) and modeling the artefacts induced by the 3D printing. Once scanned under different configurations, it is possible to assess the goodness of fit of the approximation for a noisy and potentially gappy point cloud and compare it with the traditional but less flexible NURBS. The advantages of T-splines local refinement open the door for further applications within a geodetic context such as rigorous statistical testing of deformation. Two different scans from a slightly deformed object were approximated; we found that more than 40% of the computational time could be saved without affecting the goodness of fit of the surface approximation by using the same mesh for the two epochs.

Download Full-text

Comparison of Depth Camera and Terrestrial Laser Scanner in Monitoring Structural Deflections

Sensors ◽

10.3390/s21010201 ◽

2020 ◽

Vol 21 (1) ◽

pp. 201

Author(s):

Michael Bekele Maru ◽

Donghwan Lee ◽

Kassahun Demissie Tola ◽

Seunghee Park

Keyword(s):

Optical Sensors ◽

Point Cloud ◽

Three Dimensional ◽

Laser Scanner ◽

Point Clouds ◽

Depth Camera ◽

Terrestrial Laser Scanner ◽

Cloud Data ◽

3D Point Clouds ◽

3D Information

Modeling a structure in the virtual world using three-dimensional (3D) information enhances our understanding, while also aiding in the visualization, of how a structure reacts to any disturbance. Generally, 3D point clouds are used for determining structural behavioral changes. Light detection and ranging (LiDAR) is one of the crucial ways by which a 3D point cloud dataset can be generated. Additionally, 3D cameras are commonly used to develop a point cloud containing many points on the external surface of an object around it. The main objective of this study was to compare the performance of optical sensors, namely a depth camera (DC) and terrestrial laser scanner (TLS) in estimating structural deflection. We also utilized bilateral filtering techniques, which are commonly used in image processing, on the point cloud data for enhancing their accuracy and increasing the application prospects of these sensors in structure health monitoring. The results from these sensors were validated by comparing them with the outputs from a linear variable differential transformer sensor, which was mounted on the beam during an indoor experiment. The results showed that the datasets obtained from both the sensors were acceptable for nominal deflections of 3 mm and above because the error range was less than ±10%. However, the result obtained from the TLS were better than those obtained from the DC.

Download Full-text

Accuracy assessment of a mobile terrestrial laser scanner for tree crops

Advances in Animal Biosciences ◽

10.1017/s2040470017000073 ◽

2017 ◽

Vol 8 (2) ◽

pp. 178-182 ◽

Cited By ~ 1

Author(s):

F. H. S. Karp ◽

A. F. Colaço ◽

R. G. Trevisan ◽

J. P. Molin

Keyword(s):

Data Acquisition ◽

Spatial Data ◽

Accuracy Assessment ◽

Laser Scanner ◽

Terrestrial Laser Scanner ◽

Tree Crops ◽

Area Estimation ◽

Gnss Receiver ◽

Truncated Cone ◽

Set Up

LiDAR technology is one option to collect spatial data about canopy geometry in many crops. However, the method of data acquisition includes many errors related to the LiDAR sensor, the GNSS receiver and the data acquisition set up. Therefore, the objective of this study was to evaluate the errors involved in the data acquisition from a mobile terrestrial laser scanner (MTLS). Regular shaped objects were scanned with a developed MTLS in two different tests: i) with the system mounted on a vehicle and ii) with the system mounted on a platform running over a rail. The errors of area estimation varied between 0.001 and 0.071 m2 for the circle, square and triangle objects. The errors on volume estimations were between 0.0003 and 0.0017 m3, for cylinders and truncated cone.

Download Full-text

The Horizontal Deformation Analysis of High-rise Buildings

Proccedings of 10th International Conference "Environmental Engineering" ◽

10.3846/enviro.2017.194 ◽

2017 ◽

Author(s):

Žymantas Gražulis ◽

Boleslovas Krikštaponis ◽

Algirdas Neseckas ◽

Darius Popovas ◽

Raimundas Putrimas ◽

...

Keyword(s):

Power Plants ◽

Laser Scanning ◽

Thermal Power ◽

Laser Scanner ◽

Deformation Analysis ◽

Terrestrial Laser Scanner ◽

Horizontal Deformation ◽

Cloud Data ◽

High Rise ◽

Cloud Data Processing

The horizontal deformation analysis of high-rise buildings, quite often is complicated because buildings like chimneys, towers and etc, have complex and asymmetric shapes, consequently there is not always the possibility to apply the method of single points motion analysis. Furthermore, the horizontal deformation analysis is complicated using standard measurement methods like measurements with electronic total stations or optical theodolites. In such case the terrestrial laser scanner could be superior to traditional measurements. However, the terrestrial laser scanner still not widely used to survey building horizontal deformations using high precision measurements. The main aim of this work is to determine the suitability to measure deflections of buildings from the vertical using terrestrial laser scanners and to investigate point cloud data processing. Measurements of horizontal deformation were carried out using the over ground laser scanner and electronic total station. Horizontal deformations of chimneys of thermal power plants were investigated using corresponding methods. Deformation indicators and evaluated measurement accuracies between different methods were compared. Data analysis of terrestrial laser scanning is more complex, time consuming and requires sophisticated hardware resources in comparison with the traditional methods, however results are much more detailed and informative.

Download Full-text

Explanation for the seam line discontinuity in terrestrial laser scanner point clouds

ISPRS Journal of Photogrammetry and Remote Sensing ◽

10.1016/j.isprsjprs.2019.05.012 ◽

2019 ◽

Vol 154 ◽

pp. 59-69 ◽

Cited By ~ 2

Author(s):

D.D. Lichti ◽

C.L. Glennie ◽

K. Al-Durgham ◽

A. Jahraus ◽

J. Steward

Keyword(s):

Laser Scanner ◽

Point Clouds ◽

Terrestrial Laser Scanner

Download Full-text

Displacement Study of a Large-Scale Freeform Timber Plate Structure Using a Total Station and a Terrestrial Laser Scanner

Sensors ◽

10.3390/s20020413 ◽

2020 ◽

Vol 20 (2) ◽

pp. 413 ◽

Cited By ~ 1

Author(s):

Anh Chi Nguyen ◽

Yves Weinand

Keyword(s):

Large Scale ◽

Numerical Models ◽

Laser Scanner ◽

Experimental Tests ◽

Point Clouds ◽

Element Model ◽

Experimental Investigations ◽

Bottom Surface ◽

Terrestrial Laser Scanner ◽

Total Station

Recent advances in timber construction have led to the realization of complex timber plate structures assembled with wood-wood connections. Although advanced numerical modelling tools have been developed to perform their structural analysis, limited experimental tests have been carried out on large-scale structures. However, experimental investigations remain necessary to better understand their mechanical behaviour and assess the numerical models developed. In this paper, static loading tests performed on timber plate shells of about 25 m span are reported. Displacements were measured at 16 target positions on the structure using a total station and on its entire bottom surface using a terrestrial laser scanner. Both methods were compared to each other and to a finite element model in which the semi-rigidity of the connections was represented by springs. Total station measurements provided more consistent results than point clouds, which nonetheless allowed the visualization of displacement fields. Results predicted by the model were found to be in good agreement with the measurements compared to a rigid model. The semi-rigid behaviour of the connections was therefore proven to be crucial to precisely predict the behaviour of the structure. Furthermore, large variations were observed between as-built and designed geometries due to the accumulation of fabrication and construction tolerances.

Download Full-text