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

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"[m] of system 90%) 3540 distance based are 45 plotted 50Figure measurement'static and 3.11: refer Repeatabilitymode'. to the Three same repeated setup. data series on awhite target (reflectivity,I34 3. Calibration of Terrestrial Laser Scannerlaser scannerplanar targetinterferometertrolleyI i i i ii ii i i | i i i i i i i i i | i i i il ri ( i | i i i ri i i i i | i i r i i i i i i |distance (interferometer)distance (laser scanner)calibrated distanceFigure 3.10:Calibration setup for the distance measurement system in the 'static mode' of the laser scanner usingplanar targets.Figure 3.11 shows the deviation between the derived mean value acquired bythe laser scanner and thenominal value provided by the interferometer. The results are three lines representing the accuracy of thedistance measurement system.constant and a scale factor cannot be seen.First, an overall and reproducible systematic trend caused bySecond, specific sections showingan additivea similar behaviour can beassumed but without trustworthy results. Calibration curves based on harmonic oscillations can be derivedand can be applied for improving the curves of the mean values. However,the more important aspect isthat all three lines are within ±5 mm according to the manufacturers' specifications on the linearity error.These results were confirmed by additional investigations.It should be mentioned that the calibration curves are dependent on several parameters, e.g. the reflectivityand the angle of incidence. Calibration curves have to be defined regarding these parametersfor the sakeof completeness. In previous investigations, multipath effects, which were caused by the background, wereseen, cf. [Ingensand et al., 2003]. The divergence of the laser beam enlarged the footprint to the point ofovertopping at a specific distance. To avoid these affects in following investigations,installed in the background. Furthermore, an upgrade of the laser scanner in February,beam divergence.a velvet curtain was2004 narrowed the10reflectivity 90% (white)iV.-~A/VY^
tions of the manufacturer, it can be concluded that the specifications track definedbetween areforthen being laser been was linepoint. center.cannot met, similar^90%cf. This scanner with since (white) tonominal they inves¬ of and di¬ —-60% B.rectly. have 3.2.2 target. (grey) In /-^~NThese Section\A.20% Mode 'static (dark 3.1.5,mode'. spheres AVi4Ï/\x^1A1/\t\/\s targets were \f/x iv*^ \ll used \> \**St\Ahu\h\hyV«-1 K*1*, y? had /yVderiving 'scanningcalibrationperformedcompared horizontalwell-suitedacquired Appendix importancedistancesawell-definedScanninginvestigationintroducedproperty adefinitely3.2 Distance Measurement System 35AccuracyThe accuracy of the distance measurement system based on different reflectivity values for the targets hasalready been analyzed. The question is is there a systematic deviation of the distance measurement systemfor a specific reflectivity?The results for specific reflectivity values are shown in Figure 3.12.The curves are similar to the resultsobtained by the investigation for repeatability. The conclusion is that the reflectivitydoes not influence themean value of the distance measurement system. Furthermore, the accuracy meets the requirement of themanufacturer for covering the full measuring range of 50 m. However, the correspondingmean values donot mean that the noise of the measurements, i.e.the precision,is also similar.10distance accuracy1"E5ou-5'"0 5 10 15 20 25 30 35 40 45 50range [m]Figure 3.12: Accuracy of the distance measurement system based on the 'static mode'. The targets used have differentvalues of reflectivity, namely 90% (white), 60% (grey) and 20% (dark grey).PrecisionThe precision defines the noise of a sensor. In terms of the laser scanner, the precisionsurement system gives an estimation for the empirical standard deviation of a singleof the distance mea¬distance measurement.The precision is a reliable parameter since it defines the imprecision of a single shot that occurred during ascanning process and helps to assess each single point in the point cloud.Figure 3.13 shows the standard deviation over the measuring range of 50 m for the three targets with dif¬ferent reflectivity values. It can be seen that up to a range of 10 m, the curves are close to each other with aprecision of less than 2 mm. As the lines are diverge, a difference between the reflectivity values is clearlyvisible. Since the standard deviation represents 1 a noise, the area covering each measurement, i.e. 99.9 %,has to be multiplied by a factor of three. The increasing noise is correlated to the decreasing intensityin thereflected laser beam and defines the signal-to-noise ratio (SNR). Comparing these results to the specifica¬
Page 1: DISS. ETH NO. 17036Calibration of a
Page 5 and 6: 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
Page 20 and 21: 10 2. Components of Terrestrial Las
Page 34 and 35: 24 3. Calibration of Terrestrial La
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Page 46 and 47: !36 3. Calibration of Terrestrial L
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Page 68 and 69: Inormal axis,intersectionpoint axis
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Page 84 and 85: 74 4. Static Laser Scanning4.1.2 Mi
Page 86 and 87: 76 4. Static Laser ScanningOptical
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84 4. Static Laser Scanning4.3.3 NU
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86 4. Static Laser Scanning
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88 5. Kinematic Laser Scanningmirro
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90 5. Kinematic Laser ScanningThe a
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92 5. Kinematic Laser Scanninghas a
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'94 5. Kinematic Laser Scanningbeam
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''iI98 5. Kinematic Laser ScanningA
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102 5. Kinematic Laser Scanning5.3
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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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