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

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48 3. Calibration of Terrestrial Laser Scanner±LFigure 3.24: Determination of the angular resolution. The point spacing a in a distance s defines the angularresolution 9.Table 3.7: Angular resolution of the deflection unit derived by three different scanning modes: 'middle', 'high' and'superhigh'.Deflection Direction Parameter Middle High Superhighsub-sampling 4 2 1# points 6 13 7horizontal distance [mm] 40 45 12point spacing [mm] 6.7 3.5 1.7actual resolution [°] 0.068 0.035 0.017angularresolution [°] 0.017 0.018 0.017sub-sampling 4 2 1# points 7 15 7vertical distance [m] 43 50 11point spacing [mm] 6.1 3.3 1.6actual resolution [°] 0.062 0.034 0.016angularresolution [°] 0.016 0.017 0.016The angular resolution is not only dependent on the deflection unit. The spot size defined bydivergence and the resulting footprinthas also to be taken into account. Theunit should not be smaller than the spot size since two adjacent footprints overlapthe beamincrement of the angulareach other. [Lichti andJamtsho, 2006] introduced the effective instantaneous field of view (EIFOV) as a new parameter for definingthe angular resolution of terrestrial laser scanners by considering both the angular resolution, i.e. samplinginterval, and the spot size, i.e. laser beamwidth.3.4 Instrumental ErrorsThis section discusses some of the major instrumental errors that can influence each single measurement.In contrast to the sections before, cf.distance measurement system and angle measurement system, thepossible errors due to the mechanical realization of the laser scanner are investigated, e.g.the well-knowninstrumental errors of theodolites: eccentricities, wobble of rotation axes, error of collimation axis, and errorof horizontal axis, i.e. tilting axis. This approach is valid since the working principle and design of the laserscanner corresponds to the working principle and designof theodolites and laser trackers.
3.4 Instrumental Errors 493.4.1 Eccentricity of Scan CenterThe ideal construction of a rotating instrument assumes that the real center of rotation correspondsideal center of rotation. If there is a deviation due to mechanical imperfections,is present. The laser scanner system to be calibrated has two different rotations: a primaryto thethen an instrumental errorrotation aboutan horizontal axis, i.e. tilting axis, and a secondary rotation about a vertical axis, i.e. rotation axis. In thefollowing, an examination of the eccentricity of the laser scanner center is presented. In particular, twodifferent aspectsare discussed:• the eccentricity of the vertical axis• the eccentricity of the scan centerInfluences caused by errors in the horizontal axis are discussed separately,investigations were carried out in such a way that errors caused bycf. Section 3.4.4.All describedthe horizontal axis do not influence theinvestigations. All objects to be scanned, e.g. spheres, were positioned horizontally and at the same height.Thus, errors resulting from the horizontal axis can either be eliminated or they have the same influence onall the object points. Possible errors caused by the distance measurement system, e.g. additive constant,scale factor, also have to be reduced from the measurements.The objective is to verify that the laser scanner can be mounted on a tripod or on an observation pillar, likea total station.This means the laser scanner can be centered on a control point and the rotation center ofthe vertical axis corresponds to the center of this control point. Furthermore, the origin of the local scannersystem has to conform with the rotation center. The setup of a laser scanner can be analogous to that of atotal station. First, a tribrach is mounted on a tripod or on an observation pillar and is then levelled usinga plate level, which is attached securely on the laser scanner. Second, an adapter platetribrach. Third, the laser scanner is installed on this adapter plate and is readyand the rotation axes can be seen in Figure 3.25.is fixed onto thefor use. The laser scannervertical axis— — —horizontal axisFigure 3.25: Principle of the laser scanner and the axes of rotation. The laser scanner has two axes of rotation: aprimary fast rotation about the horizontal axis and a secondaryslow rotation about the vertical axis.Eccentricity of Vertical AxisThe investigation of the eccentricity of the vertical axis covers two aspects: the rotation has to be homoge¬nous, i.e.resulting in a circle, and the center pointof this circle has to fit the nominal center of the controlpoint on which the laser scanner was set up. This examination requires high precision regardingthe sur¬veying of a target that is mounted on top of the laser scanner and represents the rotation of the laser scanner.
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DISS. ETH NO. 17036Calibration of a
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ZusammenfassungSeit einigen Jahren
Page 7 and 8: ContentsAbstractiiiZusammenfassungv
Page 9 and 10: Contentsix6.1.3 Results Ill6.2 Stat
Page 11 and 12: 1Introduction1.1 Terrestrial Laser
Page 13: 1.2 Motivation 3Precision [m10~1 "1
Page 16 and 17: 6 1. Introduction
Page 18 and 19: 8 2. Components of Terrestrial Lase
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Page 84 and 85: 74 4. Static Laser Scanning4.1.2 Mi
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''iI98 5. Kinematic Laser ScanningA
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102 5. Kinematic Laser Scanning5.3
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—1.104 5. Kinematic Laser Scannin
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propagationresults series Taylorter
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108 5. Kinematic Laser Scanningonly
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cf.aroundframe regardingsetupusinga
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112 6. Applications of Terrestrial
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acquisitiondescribingFinally, thatM
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132 7. Summaryrange, achievable by
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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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