Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...

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84 4. Static Laser Scanning4.3.3 NURBSNURBS is anacronym for non-uniform rational B-splines. The first publications of NURBS refer to [Riesen¬feld, 1973] and [Versprille, 1975]. A NURBS can be described either by a curve or bymathematical descriptions can be found in [Piegl, 1991].a surface. DetailedFor laser scanning, the use of NURBS is becoming important since the surveyed objects described by thepoint cloud cannot only be modeled with geometrical primitives but also with free-form shapes.NURBSis an efficient tool for approximating free-form curves and surfaces. According to [Piegl, 1991], some of theadvantages of NURBS are they• offer a common mathematical form for standard analytic shapes and free-form curves and surfaces,• provide the flexibility to design a large variety of shapes,• have clear geometrical interpretations,• have a powerful geometrical tool kit,• are invariant regarding scale, rotation, translation, and• are genuine generalizations of non-rational B-splinecurves and surfaces.forms as well as rational and nonrational BézierSome drawbacks of NURBS are they require extra storage to define traditional curves and surfaces and theycan result in very poor parameterization due to improper use of required parameters.Designing NURBS can be carried out in two ways, interpolation and data filtering. Interpolating meansgeometrical functions are fitted into a given set of control points to derive a new set of data. Interpolatingcan produce erroneous results due to the existence of noise or blunders. A better solution is an approxima¬tion of the given set of data by fitting geometrical functions close to the given data set and by passing onlya few of them. The most popular approximation is least-squares fitting. The result of least squares fitting isa smoothed and less-biased description of the data set.NURBS has become widely accepted and popular, especially in computer-aided design (CAD), computeraidedmanufacturing (CAM), and computer-aided engineering (CAE), and the graphics community.Figure 4.6: Examples for NURBS modeling and rendering, from left to right: squirrel, sailing yacht, airport[Rhinoceros®, 2006].
4.3 Modeling and Visualization 854.3.4 CADComputer-aided Design (CAD) is a computer-based tool to design and develop 2D drawingsor 3D mod¬els. CAD is used in many fields, such as architecture, building engineering and mechanical CAD, e.g.automotive, aerospace, ship building. Within the product lifecycle management process,geometry authoring tool, cf. Figure 4.7.CAD is the mainThere are various different software packages available on the market, e.g. AutoCAD, Microstation, Solid-Works. Depending on the application area, the most suitable software has to be chosen. Compared to3D point cloud software, the drawback of CAD software isimported into the CAD software. Either the point cloud has to be processedonly a limited number of points that can beand reduced beforehand or ad¬ditional tools have to be used, such as CloudWorx, which allows one to work in the AutoCAD environmentbut also allows access to the whole point cloud.DesignDevelopConceiveManufactureideaCADToolXMi\Concept DesignDetailed ComponentModelingDesign^ EngineeriigDrawingsx%\Product LayoutRequirementsBottoHmpeonstmetott AssemblyModelingN^"01«Analysis\cueValidateFigure 4.7: CAD and the manyfields of applications, adaptedfrom [Wikipedia, 2006].4.3.5 Rendering and Texture MappingSince CAD models or NURBS models do not show a realistic image of the object,the derived model canbe processed by rendering or texture mapping. Rendering is the process of improving the appearance ofthe object by introducing lightsources or other visual effects. Texturemapping means that digital images,either images of the real object or patterns, are mapped onto the model in perspective view. Such processesare often necessary to provide impressive and realistic models for marketing and visualization purposes.Some examples are shown in Figure 4.6.For such purposes, visualization graphics libraries are required.The most-used libraries are OpenGL, VRML, Java3D and Direct3D [Hovenbitzer, 2003].
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DISS. ETH NO. 17036Calibration of a
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ZusammenfassungSeit einigen Jahren
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ContentsAbstractiiiZusammenfassungv
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Contentsix6.1.3 Results Ill6.2 Stat
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1Introduction1.1 Terrestrial Laser
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1.2 Motivation 3Precision [m10~1 "1
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6 1. Introduction
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8 2. Components of Terrestrial Lase
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10 2. Components of Terrestrial Las
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24 3. Calibration of Terrestrial La
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134 7. Summary
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136 A. Imaging System of Imager 500
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138 B. Technical Data of Imager 500
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u140 C. Adjustment of SphereA =dfi,
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142 C. Adjustment of Sphere
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144 D. Electronic Circuit for Deter
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aMulti-SensorPlatform,PhDGeodesy Sw
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Accuracy-AeinTPS1200 AG, -Version 1
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-GenauigkeitsbetrachtungenInvestiga
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152 BibliographyWunderlich, T. A. [
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List of Figures3.22 Residuals of th
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156 List of Figures
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158 List of Tables
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200220072002Curriculum VitaePersona
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