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

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26 3. Calibration of Terrestrial Laser Scanner3.1 Laboratories and Tools for CalibrationThe IGP is equipped with various kinds of laboratory facilities, test fields, etc. Thus, geodetic instrumentscan be calibrated regarding different aspects.In the following, some laboratory facilities and test fields,which play an important role in the calibration of the terrestrial laser scanner, are introduced.3.1.1 Calibration Track LineThe calibration track line at the IGP has a length of roughly 52 m. A trolley moves on the track line, eitherautomatically or manually, cf. Figure 3.2. This trolley is tracked by a laser metric system (HP 5529A dy¬namic calibrator), which is based on interferometry. Thus, the position of the test trolleyon this track linecan be located within a high accuracy of less than 0 1 mm1. Atmospheric conditions , i.e. air temperature,air pressure and air humidity, are also collected as they are required for atmosphericmeasured by the interferometer to guarantee high accuracy.Therefore, lab conditions aretemperaturestabilizedby air conditioning within a temperature rangecorrection of distancesof 20 °C ± 0 5°C.The distance measurementsystem of geodetic instruments can be calibrated by comparing the measured distances acquired by theinstrument to be calibrated with the nominal distances provided bythe interferometer.Therefore, the in¬strument to be calibrated is set up at the beginning of the track line in a way that the instrument is alignedin extension with the track line.An observation pillar is installed and facilitates the required setup easily.On the test trolley, a target can be mounted to measure the distances between the test trolleyand the instru¬ment. The additive constant between the mechanical zero point of the track line and the observation pillaris calibrated and well-known. Thus, relative as well as absolute distance measurements can be performed.Figure 3.2: Calibration track line with a length of52 m including the test trolley movingon the track line.The 3D trajectory of the calibration track line is checked periodically. The optimal track can be approx¬imated by a line that should run straight horizontally and vertically.Since an optimal straightline canrarely be established, the real run of the track line has to be identified. Generally, three different parametersare required: the straightness of alignment, the verticality of alignment and the cant, i.e.ent. The trajectory of the calibration track line regarding these parameters are shown in Figureupper figure, the straightness of alignment and the verticality of alignmentcan be seen.transverse gradi¬3.3. In theThe variation inthe vertical direction shows a maximum relative value of 1 mm. According to Abbes comparator principle,the laser beam of the interferometer and the measurement beam of the instrument to be checked has tobe in a straight line.Since this constraint can rarely be met with the designthe verticality of alignment is of great importance. But the maximum changeof the calibration track linein the vertical direction can1This accuracy represents for the resulting accuracy of the mechanical zero point of the calibration track line, the orientation of thetest trolley and the accuracy of the laser interferometer The accuracy of the HP interferometer is given by 0 2 /im + 05 10 ~6 D,where D is the distance m [m], the resolution is given by 0 1 /im
^-3.1 Laboratories and Tools for Calibration 27be stated by a value of 0.5 mm in 2 m, cf. Figure 3.3.Since the vertical offset between interferometer andinstrument is far below 2 m, this influence can be neglected. The variation in the straightness of alignmentshows an increasing deviation up to 3 mm in arangestraight distance is far below the desired distance accuracy. In the lower figure,of 50 m. The influence of this deviation on the desiredthe cant of the track can beseen and is relatively small and thus, negligible. In summary, the track line is well-adjusted regarding thestraightness of alignment, the verticality of alignmentcalibration procedures that will result in a high accuracy.and the cant.The trajectory of the calibration track line is not of importancement systems of geodetic instruments in static applications.Thus, this track line is well-suited forto the calibration of the distance measure¬The small variations of the track do not influ¬ence the operation of the laser interferometer and does not significantly influence the ranges measured bythe geodetic instruments.In addition, for kinematic applications, the 3D trajectory of the moving instru¬ment has to be known in terms of the position (x, y, z) and in terms of the attitude angles {to, -3.0—•—straightness of alignment-*verticality of alignment~"t 10 20 30 40 50 0 10 20 30 40range [m]0.4E0.2££ o.O'co-0.2"°"40 5 10 15 20 25 30 35 40 45 50range [m]Figure 3.3: Trajectory of the calibration track line. In the upperfigure, the straightness of alignment and the vertical¬ity of alignment can be seen. In the lower figure, the cant of the track is shown.The wall behind the interferometer of the calibration track line, cf. Figure 3.10, is covered with a darkvelvet curtain to avoid reflections from the background, which would resulting in mixed pixels, blundersor multipaths.3.1.2 Test Field of Control PointsAlong the calibration track line, a test field of control points was installed. It consists of observation pillarslocated beside the track line and bolts drilled into concrete walls. These control points are located along thecalibration track line at both sides and at different heights. The location of the points can be seen in Figure3.4. The coordinate system is oriented in such a way that the track of the test trolleydefines the x-axis.
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
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76 4. Static Laser ScanningOptical
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78 4. Static Laser Scanningmaximum
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80 4. Static Laser Scanningand gene
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82 4. Static Laser Scanning• Ther
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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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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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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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