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

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'94 5. Kinematic Laser Scanningbeam is not punctiform, but has a more complex structure during propagation in the air, cf. Section 2.1.2.If the laser beam hits an object, a footprint of the laser beam is generated.Therefore, the 'real' footprintis much larger than the 'visible' footprint. Furthermore, the sensitivity of the diodes is important. Only asmall part of the laser beam needs to hit the photo diode to start the process.If another part of the laserbeam hits the photo diode directly a second time, the stopping process is performed.Neither does the laserbeam rotate 2tt nor can a reproducible and reasonable rotation time T be derived. To avoid these problems,either a more complex electronic circuit has to be developed or two photothem have to be implemented. The latter was used in this study.diodes with a distance betweenThe use of two photo diodes implicates some specialties with respect to the experimental setup. Addition¬ally, the center angle a has to be determined. Referring to the postulation regarding the precisionof therotation time T, the required precision for the center angle a can be estimated. To achieve the best possibleprecision for the center angle a, the principleof autocollimation was used. InFigure 5.4, the two photodiodes, as well as the autocollimation mirror mounted on a plate, can be seen. This plate can be aligned byan adjusting device.autocollimationmirrordiode(stop)centre laser beam(rotating mirror]diode(start)Figure 5.5: Mathematical relations for deriving the center angle a: the radius r,be known.the base b and the offset Ar has toIn Figure 5.5, the mathematical relation between the desired center angle a, the plate including the photodiodes, and the autocollimation mirror can be seen. The center angle a can be caluclated bya = 2 •arctan-2(r Ar)(5.5)where r is the radius, i.e.distance between center of rotating mirror and autocollimation mirror, Ar is theoffset between the photodiodes and the autocollimation mirror and b is the base i.e.the distance betweenthe two diodes. The offset Ar was measured with a slide gauge several times. As result, the offset Ar is lessthan 0.5 mm with a precision of about 0.1 mm. Considering Equation (5.5), the influence of Ar is negligible,if the radius r is larger than 0.5 m. The reason is that, assuming the slowest angular freqeuncy of 12.5 rps2,the influence on the rotation time T is less than the time precision of 1/xs claimed. Thus, Equation (5.5)simplifies to a = 2 •arctan2r(5.6)2Rps: rotations per second. According to the specifications of the manufacturer, there are three different rotating velocities: ojns12.5rps(Tfa0.08s),w25 fa 25rps (T fa 0.04 s) and w33 fa 33 rps (T fa 0.03 s)
5.2 Rotation Time of Rotating Mirror of Laser Scanner 95The questionsraised now are: (1)How precisely does the center anglea have to be determined or what isthe influence of the parameters base b and radius r. And (2) how accurate is the autocollimation.(1) Precision of center angle aApplying the propagation of errors and forming the total differential equation for Equation (5.6), the errorfor the center angle a can be estimated. Alternatively, the influence of the two parameters base b and radiusr can be identified:*=(%)'* + (%)'*
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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 54 and 55: 44 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 110 and 111: 40323 o.o; 50545 aT [jjs] 1.0().2 S
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Page 116 and 117: propagationresults series Taylorter
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Page 122 and 123: 112 6. Applications of Terrestrial
Page 136 and 137: acquisitiondescribingFinally, thatM
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
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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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