scholarly journals Detection of periodic displacements of shell structures with edges using spline surfaces, meshes and point clouds

2021 ◽  
Vol 112 (1) ◽  
pp. 27-33
Author(s):  
Grzegorz Lenda ◽  
Katarzyna Abrachamowicz
Keyword(s):  
Laser Scanning ◽  
Point Clouds ◽  
Shell Structures ◽  
Triangle Mesh ◽  
Advantages And Disadvantages ◽  
Mesh Model ◽  
Spline Surfaces ◽  
Continuous Models ◽  
Correct Determination ◽  
Comparison Of The Results

Abstract This research paper tackles the problem of determining displacements of complex-shaped shell structures, measured periodically using laser scanning. Point clouds obtained during different measurement epochs can be compared with each other directly or they can be converted into continuous models in the form of a triangle mesh or smooth patches (spline functions). The accuracy of the direct comparison of point clouds depends on the scanning density, while the accuracy of comparing the point cloud to the model depends on approximation errors that are formed during its creation. Modelling using triangle meshes flattens the local structure of the object compared to the spline model. However, if the shell has edges in its structure, their exact representation by spline models is impossible due to the undulations of functions along them. Edges can also be distorted by the mesh model by their chamfering with transverse triangles. These types of surface modelling errors can lead to the generation of pseudo-deformation of the structure, which is difficult to distinguish from real deformation. In order to assess the possibility of correct determination of deformation using the above-mentioned methods, laser scanning of a complex shell structure in two epochs was performed. Then, modelling and comparison of the results of periodic measurements were carried out. As a result of the research, advantages and disadvantages of each method were identified. It was noticed that none of the methods made it possible to correctly represent all deformations while suppressing pseudo-deformation. However, the combination of their best qualities made it possible to determine the actual deformation of the structure.

scholarly journals EXPLORING ALS AND DIM DATA FOR SEMANTIC SEGMENTATION USING CNNS

2018 ◽  
Vol XLII-1 ◽  
pp. 347-354 ◽  
Author(s):  
F. Politz ◽  
M. Sester
Keyword(s):  
Point Cloud ◽  
Laser Scanning ◽  
Semantic Segmentation ◽  
Point Clouds ◽  
Good Alternative ◽  
Aerial Images ◽  
Learning Approaches ◽  
Advantages And Disadvantages ◽  
Sensing Applications ◽  
High Level

<p><strong>Abstract.</strong> Over the past years, the algorithms for dense image matching (DIM) to obtain point clouds from aerial images improved significantly. Consequently, DIM point clouds are now a good alternative to the established Airborne Laser Scanning (ALS) point clouds for remote sensing applications. In order to derive high-level applications such as digital terrain models or city models, each point within a point cloud must be assigned a class label. Usually, ALS and DIM are labelled with different classifiers due to their varying characteristics. In this work, we explore both point cloud types in a fully convolutional encoder-decoder network, which learns to classify ALS as well as DIM point clouds. As input, we project the point clouds onto a 2D image raster plane and calculate the minimal, average and maximal height values for each raster cell. The network then differentiates between the classes ground, non-ground, building and no data. We test our network in six training setups using only one point cloud type, both point clouds as well as several transfer-learning approaches. We quantitatively and qualitatively compare all results and discuss the advantages and disadvantages of all setups. The best network achieves an overall accuracy of 96<span class="thinspace"></span>% in an ALS and 83<span class="thinspace"></span>% in a DIM test set.</p>

scholarly journals INTEGRATION OF PHOTOGRAMMETRY, COMPUTED TOMOGRAPHY AND ENDOSCOPY FOR GYROSCOPE 3D DIGITIZATION

2021 ◽  
Vol XLVI-M-1-2021 ◽  
pp. 925-931
Author(s):  
K. Zhan ◽  
D. Fritsch ◽  
J. F. Wagner
Keyword(s):  
Computed Tomography ◽  
Cultural Heritage ◽  
Laser Scanning ◽  
Point Clouds ◽  
Control Points ◽  
Heritage Preservation ◽  
Color Mapping ◽  
Advantages And Disadvantages ◽  
3D Digitization ◽  
Cultural Heritage Preservation

Abstract. Cultural heritage preservation via 3D digitization is becoming more and more important. Besides conventional buildings and landmarks, many technical instruments and artifacts, which belong to tech heritage (TH), are also of great importance, historically and didactically. Gyroscopes, which can be dated back for 200 years, are fascinating instruments with complex structures and different working principles. With such properties, any 3D digitization of Gyroscopes could not be realized by simply using conventional solutions of photogrammetry or laser scanning. In our work, we introduce photogrammetry, endoscopy and computed tomography (CT) for an integrated 3D digitization solution. Though photogrammetry has been widely used for the purpose of cultural heritage preservation, 3D reconstructions using the other two sensor systems have their own challenges. For an endoscope, a pre-calibration solution has been put forward and the Structure-from-Motion (SfM) process has been optimized to deal with the drift caused by a long imaging trajectory. Regarding the CT 3D reconstruction, we mainly focus on the 3D representation’s completeness and the denoising process. In the section of data integration, we designed different methods according to the characteristics of the objects as well as the 3D models from different sonsors. In case of limited overlap between the pair of point clouds, the Gauss-Helmert model with manually picked control points is applied for the estimation of the transformation matrix. CT point clouds, which hold only the intensity values representing the material attenuation, could be integrated with photogrammetry data via a surface color mapping method using the photogrammetric images or the primitive based corresponding virtual control points. Through our research, the concept of integrating photogrammetry, endoscopy and CT for 3D digitization of Gyroscopes is validated. Furthermore, advantages and disadvantages involved in the complete process are discussed and a solid foundation has been laid for further research.

scholarly journals SIMULATING VARIOUS TERRESTRIAL AND UAV LIDAR SCANNING CONFIGURATIONS FOR UNDERSTORY FOREST STRUCTURE MODELLING

2017 ◽  
Vol IV-2/W4 ◽  
pp. 59-65 ◽  
Author(s):  
M. Hämmerle ◽  
N. Lukač ◽  
K.-C. Chen ◽  
Zs. Koma ◽  
C.-K. Wang ◽  
...  
Keyword(s):  
Laser Scanning ◽  
3D Structure ◽  
Tree Height ◽  
Point Clouds ◽  
Understory Vegetation ◽  
Forest Plot ◽  
Triangle Mesh ◽  
Vegetation Modelling ◽  
Efficient Planning ◽  
Scanning Strategies

Information about the 3D structure of understory vegetation is of high relevance in forestry research and management (e.g., for complete biomass estimations). However, it has been hardly investigated systematically with state-of-the-art methods such as static terrestrial laser scanning (TLS) or laser scanning from unmanned aerial vehicle platforms (ULS). A prominent challenge for scanning forests is posed by occlusion, calling for proper TLS scan position or ULS flight line configurations in order to achieve an accurate representation of understory vegetation. The aim of our study is to examine the effect of TLS or ULS scanning strategies on (1) the height of individual understory trees and (2) understory canopy height raster models. We simulate full-waveform TLS and ULS point clouds of a virtual forest plot captured from various combinations of max. 12 TLS scan positions or 3 ULS flight lines. The accuracy of the respective datasets is evaluated with reference values given by the virtually scanned 3D triangle mesh tree models. TLS tree height underestimations range up to 1.84&amp;thinsp;m (15.30&amp;thinsp;% of tree height) for single TLS scan positions, but combining three scan positions reduces the underestimation to maximum 0.31&amp;thinsp;m (2.41&amp;thinsp;%). Combining ULS flight lines also results in improved tree height representation, with a maximum underestimation of 0.24&amp;thinsp;m (2.15&amp;thinsp;%). The presented simulation approach offers a complementary source of information for efficient planning of field campaigns aiming at understory vegetation modelling.

scholarly journals MULTI-SENSOR 3D RECORDING PIPELINE FOR THE DOCUMENTATION OF JAVANESE TEMPLES

2019 ◽  
Vol XLII-2/W15 ◽  
pp. 829-834
Author(s):  
A. Murtiyos ◽  
P. Grussenmeyer ◽  
D. Suwardhi ◽  
W. A. Fadilah ◽  
H. A. Permana ◽  
...  
Keyword(s):  
Point Cloud ◽  
Laser Scanning ◽  
Cloud Model ◽  
Point Clouds ◽  
Heritage Sites ◽  
Advantages And Disadvantages ◽  
3D Point Clouds ◽  
Point Cloud Model ◽  
Geometric Quality ◽  
Different Characteristics

<p><strong>Abstract.</strong> 3D recording is an important procedure in the conservation of heritage sites. This past decade, a myriad of 3D sensors has appeared in the market with different advantages and disadvantages. Most notably, the laser scanning and photogrammetry methods have become some of the most used techniques in 3D recording. The integration of these different sensors is an interesting topic, one which will be discussed in this paper. Integration is an activity to combine two or more data with different characteristics to produce a 3D model with the best results. The discussion in this study includes the process of acquisition, processing, and analysis of the geometric quality from the results of the 3D recording process; starting with the acquisition method, registration and georeferencing process, up to the integration of laser scanning and photogrammetry 3D point clouds. The final result of the integration of the two point clouds is the 3D point cloud model that has become a single entity. Some detailed parts of the object of interest draw both geometric and textural information from photogrammetry, while laser scanning provided a point cloud depicting the overall overview of the building. The object used as our case study is Sari Temple, located in Special Region of Yogyakarta, Indonesia.</p>

scholarly journals Estimating Control Points for B-Spline Surfaces Using Fully Populated Synthetic Variance–Covariance Matrices for TLS Point Clouds

2021 ◽  
Vol 13 (16) ◽  
pp. 3124
Author(s):  
Jakob Raschhofer ◽  
Gabriel Kerekes ◽  
Corinna Harmening ◽  
Hans Neuner ◽  
Volker Schwieger
Keyword(s):  
Laser Scanning ◽  
Point Clouds ◽  
Covariance Matrices ◽  
Geometric Modelling ◽  
Deformation Analysis ◽  
Control Points ◽  
B Splines ◽  
Spline Surfaces ◽  
Standard Deviations ◽  
The Impact

A flexible approach for geometric modelling of point clouds obtained from Terrestrial Laser Scanning (TLS) is by means of B-splines. These functions have gained some popularity in the engineering geodesy as they provide a suitable basis for a spatially continuous and parametric deformation analysis. In the predominant studies on geometric modelling of point clouds by B-splines, uncorrelated and equally weighted measurements are assumed. Trying to overcome this, the elementary errors theory is applied for establishing fully populated covariance matrices of TLS observations that consider correlations in the observed point clouds. In this article, a systematic approach for establishing realistic synthetic variance–covariance matrices (SVCMs) is presented and afterward used to model TLS point clouds by B-splines. Additionally, three criteria are selected to analyze the impact of different SVCMs on the functional and stochastic components of the estimation results. Plausible levels for variances and covariances are obtained using a test specimen of several dm—dimension. It is used to identify the most dominant elementary errors under laboratory conditions. Starting values for the variance level are obtained from a TLS calibration. The impact of SVCMs with different structures and different numeric values are comparatively investigated. Main findings of the paper are that for the analyzed object size and distances, the structure of the covariance matrix does not significantly affect the location of the estimated surface control points, but their precision in terms of the corresponding standard deviations. Regarding the latter, properly setting the main diagonal terms of the SVCM is of superordinate importance compared to setting the off-diagonal ones. The investigation of some individual errors revealed that the influence of their standard deviation on the precision of the estimated parameters is primarily dependent on the scanning distance. When the distance stays the same, one-sided influences on the precision of the estimated control points can be observed with an increase in the standard deviations.

scholarly journals Spline approximation, Part 1: Basic methodology

2018 ◽  
Vol 12 (2) ◽  
pp. 139-155 ◽  
Author(s):  
Nikolaj Ezhov ◽  
Frank Neitzel ◽  
Svetozar Petrovic
Keyword(s):  
Laser Scanning ◽  
Spline Approximation ◽  
Point Clouds ◽  
Approximation Problem ◽  
Point Of View ◽  
Mathematical Function ◽  
Distributed Data ◽  
Advantages And Disadvantages ◽  
Engineering Geodesy ◽  
Different Types

Abstract In engineering geodesy point clouds derived from terrestrial laser scanning or from photogrammetric approaches are almost never used as final results. For further processing and analysis a curve or surface approximation with a continuous mathematical function is required. In this paper the approximation of 2D curves by means of splines is treated. Splines offer quite flexible and elegant solutions for interpolation or approximation of “irregularly” distributed data. Depending on the problem they can be expressed as a function or as a set of equations that depend on some parameter. Many different types of splines can be used for spline approximation and all of them have certain advantages and disadvantages depending on the approximation problem. In a series of three articles spline approximation is presented from a geodetic point of view. In this paper (Part 1) the basic methodology of spline approximation is demonstrated using splines constructed from ordinary polynomials and splines constructed from truncated polynomials. In the forthcoming Part 2 the notion of B-spline will be explained in a unique way, namely by using the concept of convex combinations. The numerical stability of all spline approximation approaches as well as the utilization of splines for deformation detection will be investigated on numerical examples in Part 3.

scholarly journals Effectiveness Analysis of Spline Surfaces Creating Methods for Shell Structures Modelling

2021 ◽  
Vol 20 ◽  
pp. 41-53
Author(s):  
Grzegorz Lenda ◽  
Dominika Spytkowska
Keyword(s):  
Laser Scanning ◽  
Model Fitting ◽  
Shell Structures ◽  
Spline Functions ◽  
Software Packages ◽  
Spline Surfaces ◽  
Modelling Techniques ◽  
Manual Selection ◽  
Modelling Efficiency ◽  
Selection Of

The shape of the surface of shell structures, measured by laser scanning, can be modelled using approximating spline functions. Since the 1990s, several modelling techniques have been developed: based on points, meshes, areas outlined on meshes, regions grouping areas with a similar structure. The most effective of them have been used in modern software, but their implementations differ significantly. The most important differences concern the accuracy of modelling, especially places with rapid shape changes, including edges. The differences also affect the mathematical complexity of the created model (the number of unknowns) and the time of its development. These factors contribute to the effectiveness of modelling. Some methods work fully automatically, others allow manual selection of certain parameters, there are also methods that require full manual control. Their selection and application is greatly affected by the user’s intuition and knowledge in the field of creating such surfaces. This study tested the influence of the above factors on the modelling efficiency. A total of six methods of creating spline surfaces were analysed in three software packages of different classes: Geomagic Design X, Solidworks and RhinoResurf. The analyses were carried out on a shell structure of complex shape, consisting of seven patches separated by edges. The created models were assessed in terms of their accuracy of fitting into the point cloud. Additionally, the complexity of the model expressed in the number of control points and the time of its development were determined. The results confirmed the validity of the four methods in terms of model fitting accuracy. The best results were achieved using the semi-automatic method in the most advanced software package and the manual method in the simplest package. This has confirmed the great importance of user experience in terms of theoretical properties of spline functions. However, complexity and development time did not show a direct relationship with the accuracy of the models created. ANALIZA EFEKTYWNOŚCI METOD TWORZENIA POWIERZCHNI SKLEJANYCH DLA MODELOWANIA OBIEKTÓW POWŁOKOWYCH Modelowanie kształtu powierzchni obiektów powłokowych, pomierzonych za pomocą skaningu laserowego, można przeprowadzić za pomocą aproksymacyjnych funkcji sklejanych. Funkcje te dobrze przybliżają kształty o ciągłej krzywiźnie, jakimi są powłoki, jednocześnie wykazując spadki dokładności w miejscach zerwania tej ciągłości. Od lat 90. XX wieku rozwinęło się kilka technik modelowania za ich pomocą, m.in.: wykorzystujących same punkty, siatki mesh, obszary obrysowane na siatkach mesh, regiony grupujące obszary o podobnej strukturze. Najbardziej skuteczne z nich zostały zastosowane we współczesnym oprogramowaniu, ale ich implementacje znacząco się pomiędzy sobą różnią. Najważniejsze różnice dotyczą dokładności modelowania, szczególnie miejsc o szybkich zmianach kształtu, włączając w nie krawędzie. Różnice dotyczą też złożoności matematycznej utworzonego modelu (liczby niewiadomych) oraz czasu jego opracowania. Czynniki te składają się na efektywność modelowania. Część metod działa w pełni automatycznie, inne pozwalają na ręczny dobór pewnych parametrów, są też metody wymagające pełnego sterowania ręcznego. W ich wyborze i stosowaniu duże znaczenie ma intuicja i wiedza użytkownika w zakresie tworzenia tego typu powierzchni. W opracowaniu przetestowano wpływ powyższych czynników na efektywność modelowania. Badaniom poddano łącznie sześć metod tworzenia powierzchni sklejanych w trzech pakietach oprogramowania różnej klasy: Geomagic Design X, Solidworks i RhinoResurf. Analizy przeprowadzono na obiekcie powłokowym o złożonym kształcie, składającym się z siedmiu płatów rozdzielonych krawędziami. Został on pomierzony metodą skaningu laserowego, a scalona chmura punktów stanowiła podstawę do modelowania za pomocą funkcji sklejanych. Utworzone modele oceniono pod względem dokładności wpasowania w chmurę punktów za pomocą wykresów odchyłek punktów od powierzchni, odchyłek średnich oraz maksymalnych. Dodatkowo określono złożoność modelu wyrażoną liczbą punktów kontrolnych oraz czas jego opracowania. Wyniki pozwoliły na potwierdzenie skuteczności czterech metod w zakresie dokładności wpasowania modeli. Najlepsze efekty osiągnięto stosując metodę półautomatyczną w najbardziej zaawansowanym pakiecie oprogramowania oraz metodę ręczną w najprostszym z pakietów. Potwierdza to duże znaczenie doświadczenia użytkownika w zakresie teoretycznych własności funkcji sklejanych. Złożoność i czas opracowania nie wykazywały natomiast bezpośredniego związku z dokładnością tworzonych modeli.

scholarly journals Overview of Available Open-Source Photogrammetric Software, its Use and Analysis

2014 ◽  
Vol 2 (4) ◽  
pp. 62-70
Author(s):  
Karol Bartoš ◽  
Katarína Pukanská ◽  
Janka Sabová
Keyword(s):  
Open Source ◽  
Laser Scanning ◽  
Time Course ◽  
Spatial Models ◽  
Point Clouds ◽  
Actual State ◽  
Optical Scanning ◽  
Advantages And Disadvantages ◽  
Wide Range ◽  
Stereo Photogrammetry

The current technological era provides a wide range of geodetic procedures and methods to document the actual state of objects on the Earth surface and at the same time course and shape of surface itself. Digital photogrammetry is one of these technologies, it allows the use of methods such as single-image photogrammetry, stereo photogrammetry (optical scanning), convergent imaging and SfM method (structure-from-motion) with final data in the form of point clouds, digital spatial models, orthophotos and other derived documents. Similar outputs can be obtained also by other technologies, mainly by terrestrial laser scanning, whilst each of the two technologies offers certain advantages and disadvantages. Especially purchasing and operating costs are one of the major drawbacks of laser scanning (while being an advantage of photogrammetry). In recent years, there has been a significant increase in development and creation of new, freely accessible (open-source) photogrammetric software, thus reducing these financial demands even more. The aim of this paper is to provide a basic overview of some of the most suitable open-source photogrammetric software and point out their strengths and weaknesses.

scholarly journals AUTOMATIC CLASSIFICATION OF TREES FROM LASER SCANNING POINT CLOUDS

2015 ◽  
Vol II-3/W5 ◽  
pp. 137-144 ◽  
Author(s):  
B. Sirmacek ◽  
R. Lindenbergh
Keyword(s):  
Point Cloud ◽  
Laser Scanning ◽  
Point Clouds ◽  
Detection Methods ◽  
Local Maxima ◽  
Advantages And Disadvantages ◽  
Close Proximity ◽  
Point Density ◽  
Grid Surface

Development of laser scanning technologies has promoted tree monitoring studies to a new level, as the laser scanning point clouds enable accurate 3D measurements in a fast and environmental friendly manner. In this paper, we introduce a probability matrix computation based algorithm for automatically classifying laser scanning point clouds into ’tree’ and ’non-tree’ classes. Our method uses the 3D coordinates of the laser scanning points as input and generates a new point cloud which holds a label for each point indicating if it belongs to the ’tree’ or ’non-tree’ class. To do so, a grid surface is assigned to the lowest height level of the point cloud. The grids are filled with probability values which are calculated by checking the point density above the grid. Since the tree trunk locations appear with very high values in the probability matrix, selecting the local maxima of the grid surface help to detect the tree trunks. Further points are assigned to tree trunks if they appear in the close proximity of trunks. Since heavy mathematical computations (such as point cloud organization, detailed shape 3D detection methods, graph network generation) are not required, the proposed algorithm works very fast compared to the existing methods. The tree classification results are found reliable even on point clouds of cities containing many different objects. As the most significant weakness, false detection of light poles, traffic signs and other objects close to trees cannot be prevented. Nevertheless, the experimental results on mobile and airborne laser scanning point clouds indicate the possible usage of the algorithm as an important step for tree growth observation, tree counting and similar applications. While the laser scanning point cloud is giving opportunity to classify even very small trees, accuracy of the results is reduced in the low point density areas further away than the scanning location. These advantages and disadvantages of two laser scanning point cloud sources are discussed in detail.

scholarly journals Towards Automated 3D Inspection of Water Leakages in Shield Tunnel Linings Using Mobile Laser Scanning Data

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6669 ◽  
Author(s):  
Hongwei Huang ◽  
Wen Cheng ◽  
Mingliang Zhou ◽  
Jiayao Chen ◽  
Shuai Zhao
Keyword(s):  
Laser Scanning ◽  
Spatial Information ◽  
Point Clouds ◽  
Tunnel Lining ◽  
Shield Tunnel ◽  
Triangle Mesh ◽  
Water Leakage ◽  
Inspection Method ◽  
3D Space ◽  
Low Efficiency

On-site manual inspection of metro tunnel leakages has been faced with the problems of low efficiency and poor accuracy. An automated, high-precision, and robust water leakage inspection method is vital to improve the manual approach. Existing approaches cannot provide the leakage location due to the lack of spatial information. Therefore, an integrated deep learning method of water leakage inspection using tunnel lining point cloud data from mobile laser scanning is presented in this paper. It is composed of three parts as follows: (1) establishment of the water leakage dataset using the acquired point clouds of tunnel linings; (2) automated leakage detection via a mask-region-based convolutional neural network; and (3) visualization and quantitative evaluation of the water leakage in 3D space via a novel triangle mesh method. The testing result reveals that the proposed method achieves automated detection and evaluation of tunnel lining water leakages in 3D space, which provides the inspectors with an intuitive overall 3D view of the detected water leakages and the leakage information (area, location, lining segments, etc.).

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