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

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''iI98 5. Kinematic Laser ScanningAfter discussing the influencing parameters in detail,some notes regarding the principle of measuringthe time delay At are necessary. For this, a special electronic device was developed,which is controlled viaparallel port (LPT). After initializing the electronic circuit, the time passed between the detection of the laserbeam on the start diode and on the stop diode is stored. Therefore, the clock generator is based on oscillatorswith different frequencies, i.e.2 MHz, 4 MHz, 8 MHz, and 16 MHz. The derived time can be read from theelectronic circuit and again a new measurement can be initialized. This procedure is repeated within aloop.The total number of time measurements as well as the time gap between each measurement can bedefined manually. The stability of the oscillators is given by 50ppm. Since 1 Hz equals 1 /xs, an instabilityin the frequency of 50 ppm leads to time variations of a single time measurement between 25 /xsfor theoscillator frequency of 2 MHz up to 3/xs for the oscillator frequency of 16 MHz. Performing repeated timemeasurements, the precision of the mean value can be increased significantly up to the desired precisionfor the rotation time T of 1 /xs. Further details regarding the electronic circuit are described in Appendix D.ResultsIn general, two independent setups, including several data series, were performed. For each setup, theautocollimation had to be carried out and the center anglea had to be derived. First, three data seriesare presented. All data series include 1000 measurements with a time interval of 1 s. The frequencyoscillator used was 2 MHz. In Figure 5.8, the detected time delay At correspondingof theto the three differentrotation velocities, i.e.12 5 rps, 25 rps, and 33 rps, are plotted. As seen, the raw data contains some blunders.The noise can be reduced by applyinga median filter.The result is a smoothed data series from which therotation time T can easily be derived. In the data series, another fact is also visible. The noise present at12 5 rps is much higher than the noise present in 25 rps and 33 rps.The reason is in mass inertia. Massinertia leads to higher noise if the rotation is slower. On the contrary, the noise decreases if the rotation isfaster.To exclude systematic effects, the Fourier analysis is appliedsignificant frequencies were present and all amplitudes were within 2 /xs. Naturally,eliminated before.on the data series. The results were noall blunders have to be0 0804300 0804200 080410*teffi^raw datamed an filter0 0804000 080390400 500 000# measurements0 0402300 040220raw datamed an filter0 0402100 040200^A/^^r-m. *#*#f#&P^W*.tW^Ce*VW#*"*%ip^jBMt« H^ifÄ**! ï*V*iV#*'«*%TkfÇ#%*500# measurementsraw datamed an filter0 030460*f**v!k*%Jjy 0^k0^. »*v%#Hi*•mWtftf***f***m#^ n»**i$j*$f#k*^ ^•f***" &+4fo+
5.2 Rotation Time of Rotating Mirror of Laser Scanner 99Second, a data set is used to verify the precision of the electronic circuit. As an example, the angular velocityof 25rps is chosen. Table 5.6 shows the reproducibility with different oscillator frequencies.The mean valuefor the time delay At, the precision of the mean value am and the precision of one single measurement asare calculated.Table 5.6:Results of the derived mean value based on 1000 measurements for the time delay At accordingangular velocity of25rps. Homogeneous results achieved by different oscillator frequenciesOscillator [MHz] At[s] CTm [/xs] as [/xs]2 0.0402071 0.1 2.44 0.0402073 0.1 2.48 0.0402072 0.1 2.616 0.0402070 0.1 2.6can be seen.to theThird, all results achieved by two different and independent setups are summarized in Table 5.7, whichcontains the mean values of the time delay At, the calculated center angle a, and the calculated rotationtime T. The two setups differ at different values for r. The radius r for setup 1 is 1.430 m, and the radius forsetup 2 is 2.900 m. The radius can be easilymeasured with the laser scanner in the so-called 'static mode'.The corresponding precision of the radius can be specified as sufficiently high with a value of ar « 2 mm.Table 5.7: Results of the measured time delay At, derived center angletent results for both setups with deviations of maximum 2 /xscan be seen.a and the calculated rotation time T. Consis¬RPS Setup Time Delay At [s] Center Anglea [°] Rotation Time T [s]12.5 10.0805260.48920.08063520.0804120.99200.08063425 10.0402620.48920.04031720.0402070.99200.04031833 10.0305020.48920.03054320.0304600.99200.030545In Table 5.7, it can be seen that with both setups, equivalent results were achieved. Hence, the desired timeresolution
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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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'28 3. Calibration of Terrestrial L
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"[m] of system 90%) 3540 distance b
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!36 3. Calibration of Terrestrial L
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138 3. Calibration of Terrestrial L
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Page 58 and 59: 48 3. Calibration of Terrestrial La
Page 68 and 69: Inormal axis,intersectionpoint axis
Page 76 and 77: j/-*'.-,•66 3. Calibration of Ter
Page 84 and 85: 74 4. Static Laser Scanning4.1.2 Mi
Page 86 and 87: 76 4. Static Laser ScanningOptical
Page 88 and 89: 78 4. Static Laser Scanningmaximum
Page 90 and 91: 80 4. Static Laser Scanningand gene
Page 92 and 93: 82 4. Static Laser Scanning• Ther
Page 94 and 95: 84 4. Static Laser Scanning4.3.3 NU
Page 96 and 97: 86 4. Static Laser Scanning
Page 98 and 99: 88 5. Kinematic Laser Scanningmirro
Page 100 and 101: 90 5. Kinematic Laser ScanningThe a
Page 102 and 103: 92 5. Kinematic Laser Scanninghas a
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Page 122 and 123: 112 6. Applications of Terrestrial
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Page 142 and 143: 132 7. Summaryrange, achievable by
Page 144 and 145: 134 7. Summary
Page 146 and 147: 136 A. Imaging System of Imager 500
Page 148 and 149: 138 B. Technical Data of Imager 500
Page 150 and 151: u140 C. Adjustment of SphereA =dfi,
Page 152 and 153: 142 C. Adjustment of Sphere
Page 154 and 155: 144 D. Electronic Circuit for Deter
Page 156 and 157: 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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