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

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22 2. Components of Terrestrial Laser Scanner2.3.2 Rotating MirrorThe primary rotation is described by a mirror that rotates about an axis The rotation axis of this primaryrotation is often a horizontal axis Thus, the laser beam is deflected in a vertical profile The secondaryrotation is carried out by the rotation of the laser scanner about a vertical axis to deflect the laser beam in ahorizontal profileencoder resolutionThe vertical sampling interval is defined by the frequency of detectingThe distance acquisition has to be synchronized with the correspondingdistances and theorientation ofthe rotating mirror Since the mirror is rotating permanently and quickly, up to 33 rotations per second, thesynchronization and the rotation time of the rotating mirror are important aspects2.3.3 Overview of Deflection Techniques in Terrestrial Laser ScannersThe following Table 2 3 gives an overview of the deflection techniquesscanners The trend is to construct panorama scanners since the advantage of a largerthat are used in terrestrial laserfield of view isobviousThe panoramascanners also include the possibility of surveyinga user-defined area instead of afull panoramaTable 2.3: Overview of deflection techniquesin terrestrial laser scannersLaser Scanner Manufacturer Deflection TechniqueCPW 8000 Callidus rotating mirrorLS 880 FARO rotating mirrorHDS 3000 Leica Geosystems oscillating mirrorLMS-Z4201 Riegl rotating polygonalmirror wheelGX Trimble scanning optical system (patented)Imager 5003 Zoller+Frohlich rotating mirror
3Calibration of Terrestrial Laser ScannerThe conception of an instrument assumes specific constraints between the different components.Due tomechanical imperfections, it is impossible to design an instrument exactly to theoretical planning. Thereare discrepancies between the real instrument and the ideal instrument, and these are called instrumentalerrors. The knowledge of instrumental errors is essential in acquiringreliable measurements. The moreone is aware of the systematic errors, the better one is able to correct for the real instrument with respectto its ideal construction by applying mathematical models. However, these mathematical models requireprecise knowledge of the instrument and its components. Furthermore, the calibration of an instrumentnecessitates the stability and the time constance of the calibration parameters. If these requirementsfulfilled, calibration is nearly impossible.are notCalibration of Terrestrial Laser ScannersComponent CalibrationSystem CalibrationDistance Measurement Systemcorrection modelsAngle Measurement SystemInstrumental ErrorsNon-Instrumental ErrorsXknowledge-basednonknowledge-basedetc.Figure 3.1: Calibration of terrestrial laser scanners, categorized by component calibration and system calibration.Normally, a distinction can be made between a system calibration and a component calibration [Hennésand Ingensand, 2000]. Figure 3.1 shows the calibration procedures. The systema mathematical model or a correction function, without knowledge of each singlecalibration derives eitherinstrumental error andits influence, by appropriate observation of control points or known objects, e.g. spheres, planes.ponent calibration is mostly based on knowledge-based modelingof the instrument and its instrumentalerrors. Each single error is investigated separately in a specific experimental setup.applied to the laser scanner, Imager 5003 of Zoller+Fröhlich, cf. Table 3.1.The com¬The latter has beenBefore starting with the discussion of the calibration procedures applied on the laser scanner, some termsand definitions need to be clarified.There is often a misunderstanding between calibration, performanceassessment/evaluation, and certification. They are similar in meaning and are often used synonymously[NIST, 2002]. However, there are slight differences in the nuances of these terms. One formal definition ofcalibration is given by [VIM, 1993]:
Page 1: DISS. ETH NO. 17036Calibration of a
Page 5 and 6: ZusammenfassungSeit einigen Jahren
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74 4. Static Laser Scanning4.1.2 Mi
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76 4. Static Laser ScanningOptical
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78 4. Static Laser Scanningmaximum
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propagationresults series Taylorter
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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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-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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