Determination of Intensity-Based Stochastic Models for Terrestrial Laser Scanners Utilising 3D-Point Clouds

Wujanz, Daniel; Burger, Mathias; Tschirschwitz, Felix; Nietzschmann, Tassilo; Neitzel, Frank; Kersten, Thomas P.

doi:10.3390/s18072187

Cited by 33 publications

(41 citation statements)

References 18 publications

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“…One of the first promising laboratory studies on the implementation of TLS in displacement and deformation measurements demonstrated that, with favourable environmental conditions, TLS measurement can be used to measure the vertical displacement down to ±0.29 mm [4]. The application of TLS in displacement and deformation measurement has been widely investigated regarding both geometry [5,6] and spectral analyses of the intensity of the reflected beam [7,8]. The papers have been partially, extensively summarised and organised by researchers from the University of Nottingham Ningbo [9].…”

Section: Introductionmentioning

confidence: 99%

TLS Measurement during Static Load Testing of a Railway Bridge

Gawronek¹,

Makuch²

2019

IJGI

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Terrestrial laser scanning (TLS) technology has become increasingly popular in investigating displacement and deformation of natural and anthropogenic objects. Regardless of the accuracy of deformation identification, TLS provides remote comprehensive information about the measured object in a short time. These features of TLS were why TLS measurement was used for a static load test of an old, steel railway bridge. The results of the measurement using the Z+F Imager 5010 scanner and traditional surveying methods (for improved georeferencing) were compared to results of precise reflectorless tacheometry and precise levelling. The analyses involved various procedures for the determination of displacement from 3D data (black & white target analysis, point cloud analysis, and mesh surface analysis) and the need to pre-process the 3D data was considered (georeferencing, automated filtering). The results demonstrate that TLS measurement can identify vertical displacement in line with the results of traditional measurements down to ±1 mm.

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Section: Introductionmentioning

confidence: 99%

TLS Measurement during Static Load Testing of a Railway Bridge

Gawronek¹,

Makuch²

2019

IJGI

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“…In this contribution, we place ourselves in the position of a TLS user wanting to account for heteroscedasticity of the TLS observations for post processing analysis. We focus on the intensity-based stochastic model as proposed in Wujanz et al [ 14 , 15 ]. This proposal has the main advantage of involving only few parameters, by having shown empirically to be accurate to describe the variance of the range measurements.…”

Section: Mathematical Backgroundmentioning

confidence: 99%

“…To account for the heteroscedasticity of range measurements, different models were derived by Ozendi et al [ 6 ], Wujanz et al [ 14 , 15 ] and Lambertus et al [ 5 ]. All proposals make use of intensity values, i.e., the optical power of the backscattered echo of the emitted signal.…”

Section: Introductionmentioning

confidence: 99%

“…The simplest model was proposed by Wujanz et al [ 14 ], who fitted the variance versus raw intensity values with a power function involving two parameters: a scaling and a power factor. For other laser scanners, the addition of a constant was necessary, i.e., a white noise contribution [ 15 ]. Focusing on the range variance for low intensities for which a correct weighting is of greater significance, different power factors were empirically found [ 20 ].…”

Section: Introductionmentioning

confidence: 99%

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On the Sensitivity of the Parameters of the Intensity-Based Stochastic Model for Terrestrial Laser Scanner. Case Study: B-Spline Approximation

Kermarrec

Alkhatib

Neumann

2018

Sensors

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For a trustworthy least-squares (LS) solution, a good description of the stochastic properties of the measurements is indispensable. For a terrestrial laser scanner (TLS), the range variance can be described by a power law function with respect to the intensity of the reflected signal. The power and scaling factors depend on the laser scanner under consideration, and could be accurately determined by means of calibrations in 1d mode or residual analysis of LS adjustment. However, such procedures complicate significantly the use of empirical intensity models (IM). The extent to which a point-wise weighting is suitable when the derived variance covariance matrix (VCM) is further used in a LS adjustment remains moreover questionable. Thanks to closed loop simulations, where both the true geometry and stochastic model are under control, we investigate how variations of the parameters of the IM affect the results of a LS adjustment. As a case study, we consider the determination of the Cartesian coordinates of the control points (CP) from a B-splines curve. We show that a constant variance can be assessed to all the points of an object having homogeneous properties, without affecting the a posteriori variance factor or the loss of efficiency of the LS solution. The results from a real case scenario highlight that the conclusions of the simulations stay valid even for more challenging geometries. A procedure to determine the range variance is proposed to simplify the computation of the VCM.

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“…• the presence of noise will significantly affect the detection of the closest point in the second epoch with the C2C algorithm. Different variances are due to the scanning geometry [11] or properties of the objects scanned [12,13]; • correlations between range measurements influence the deformation magnitude computed by reducing the number of observations available [14][15][16]. They may impact the M3C2 algorithm, depending on the radii chosen for the computation [17].…”

Section: Introductionmentioning

confidence: 99%

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

2020

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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.

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Determination of Intensity-Based Stochastic Models for Terrestrial Laser Scanners Utilising 3D-Point Clouds

Cited by 33 publications

References 18 publications

TLS Measurement during Static Load Testing of a Railway Bridge

TLS Measurement during Static Load Testing of a Railway Bridge

On the Sensitivity of the Parameters of the Intensity-Based Stochastic Model for Terrestrial Laser Scanner. Case Study: B-Spline Approximation

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

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