Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...
Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ... Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...
120 6. Applications of Terrestrial Laser Scanningthe displacements, which occurred between sessions 8 and 10, did not exceed 10 mm. Therefore, they areof the same order of magnitude as the accuracy of the laser scanning for the determination of the objectpoint displacements. However, changes in the concentration of the areas characterized by displacementsgreater than ±2 mm suggest that displacementsthe tunnel face.increased with time and with distance from the center ofFigure 6.13: Surface displacements (in [m]) obtained from comparing the point clouds acquired during sessions 9(up) and 10 (down), with the surface model correspondingto session 8.ConclusionLaser scanning is considered as a promising technique in the field of rock engineering since it has the po¬tential to be used for the collection of data required for several routine tasks. However, it is essential toselect the most appropriate laser scanner according to project-specific constraints such as range, excava¬tion geometry, time available for scanning as well as point accuracy and point density. The Imager5003 ofZoller+Frohlich was used in an experimental tunnel in the Mont Terri Rock Laboratory for the characteriza¬tion of geological discontinuities and displacement monitoring. This scanner was found to be particularlywell-suited for rock mass characterization in underground excavations while yielding an accuracyof lessthan 1 cm in the determination of the displacement of object points. Nevertheless, preliminary results sug¬gested that displacement maps with a higher order of accuracy can be produced by taking advantage ofthe large quantity of spatial data provided bythe laser scanner.displacement maps would greatly improve the understandingTherefore, the construction of accurateof the rock mass behaviour. Crucial issuesidentified for this application included referencing to a stable reference system, coordinate transformation,noise reduction and smoothing of point clouds.Regarding rock mass characterization, efforts should be made to automate the recognitionities so that the time required for data analysis can be significantlyof discontinu¬decreased. Future work will focus onthe development and comparison of processing algorithms to improve the accuracy of the displacementmapping. The resulting maps will be further compared with the results of other field investigation meth-
6.3 Kinematic Application: Test Tunnel 121ods and numerical models simulating the rock mass behaviour around the tunnel. Theaim of this studywill be to better assess the capability of laser scanning in monitoring geomechanical processes occurring inrocks.6.3 Kinematic Application: Test Tunnel6.3.1 IntroductionDue to the fast acquisition rate and the high point density, laser scanning isnot onlysuitable for staticapplications but also for kinematic applications. This is especially the case for profile measurements, whichare useful for generating an area-wide surveying of objects by means of a moving platform.The following example of a kinematic application refers to the surveyingof tunnel surfaces. Thegoal isto prove that, with kinematic laser scanning, a sufficient absolute accuracycan be achieved.faces are either scanned with static applications, using consecutive viewpoints,applications with respectto the rail axis. RelativeTunnel sur¬or with relative kinematicsurveying with respect to the rail axis is appropriate fordetecting objects dangerous to trains, i.e. railway loading gauge. However, the interpretationmations is difficult since the object, i.e. the tunnel surface, or the rails could be changedtime.of defor¬or moved withThe kinematic application is performed on a test tunnel, i.e.Zurich. The laser scanner is mounted on the test trolley, which moves alongthe calibration track line at the IGP of the ETHthe track. A total station tracksthe moving platform so that the absolute trajectory can be obtained. The laser scanner surveysvertical 2Dprofiles normal to the moving direction.During the motion, control points installed on both sides of thetrack at different heights are scanned. The 3D coordinates of the control points visualized by spheres canbe calculated. The performance and accuracy are assessed by comparing the calculated center points of thespheres with the reference coordinates based on surveying with a total station. The experimental setup wasalready shown in Section 5.1, cf. Figure 5.1, and the test field of control points alongdiscussed in Section 3.1.2.the test tunnel wasThe test trolley was forced to run with a constant velocity along the test tunnel. The control software for theencoder, causing the rotation of the wheels of the test trolley, allows a maximum velocityof 0.7 . The testtunnel and constant velocities are chosen to minimize errors for calculating the trajectory of the test trolley.Thus, the trajectory can be approximated by a regression line implying a constant velocity. A more generalmethod is the approximation of the trajectory bya Kaiman filter. TheKaiman filter can respond to varyingsystem states such as variation in the velocity. Applying both mathematical tools allow for comparing theresults and assessing the potential of kinematic laser scanning for absolute geo-referencing.The test runs for this kinematic application include• different velocities of the test trolley,• different rotation times of the rotating mirror of the laser scanner, and• different scanning resolutions.The point-spacing along the moving direction can be defined by the velocity of the test trolley and by therotation time of the rotating mirror of the laser scanner. The point-spacing within each vertical profile hasto be controlled by means of the scanning resolution according to the scanning modes supported by themanufacturer of the laser scanner.
- Page 80 and 81: 70 3. Calibration of Terrestrial La
- Page 82 and 83: 72 3. Calibration of Terrestrial La
- 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
- Page 104 and 105: '94 5. Kinematic Laser Scanningbeam
- Page 106 and 107: —96 5. Kinematic Laser ScanningTa
- Page 108 and 109: ''iI98 5. Kinematic Laser ScanningA
- Page 110 and 111: 40323 o.o; 50545 aT [jjs] 1.0().2 S
- Page 112 and 113: 102 5. Kinematic Laser Scanning5.3
- Page 114 and 115: —1.104 5. Kinematic Laser Scannin
- Page 116 and 117: propagationresults series Taylorter
- Page 118 and 119: 108 5. Kinematic Laser Scanningonly
- Page 120 and 121: cf.aroundframe regardingsetupusinga
- Page 122 and 123: 112 6. Applications of Terrestrial
- Page 124 and 125: 114 6. Applications of Terrestrial
- Page 126 and 127: 116 6. Applications of Terrestrial
- Page 128 and 129: 118 6. Applications of Terrestrial
- Page 132 and 133: 122 6. Applications of Terrestrial
- Page 134 and 135: 124 6. Applications of Terrestrial
- Page 136 and 137: acquisitiondescribingFinally, thatM
- Page 138 and 139: 128 6. Applications of Terrestrial
- Page 140 and 141: 130 6. Applications of Terrestrial
- 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
- Page 158 and 159: Accuracy-AeinTPS1200 AG, -Version 1
- Page 160 and 161: -GenauigkeitsbetrachtungenInvestiga
- Page 162 and 163: 152 BibliographyWunderlich, T. A. [
- Page 164 and 165: List of Figures3.22 Residuals of th
- Page 166 and 167: 156 List of Figures
- Page 168 and 169: 158 List of Tables
- Page 171: 200220072002Curriculum VitaePersona
120 6. Applications <strong>of</strong> <strong>Terrestrial</strong> <strong>Laser</strong> Scanningthe displacements, which occurred between sessions 8 <strong>and</strong> 10, did not exceed 10 mm. Therefore, they are<strong>of</strong> the same order <strong>of</strong> magnitude as the accuracy <strong>of</strong> the laser scanning for the determination <strong>of</strong> the objectpoint displacements. However, changes in the concentration <strong>of</strong> the areas characterized by displacementsgreater than ±2 mm suggest that displacementsthe tunnel face.increased with time <strong>and</strong> with distance from the center <strong>of</strong>Figure 6.13: Surface displacements (in [m]) obtained from comparing the point clouds acquired during sessions 9(up) <strong>and</strong> 10 (down), with the surface model correspondingto session 8.Conclusion<strong>Laser</strong> scanning is considered as a promising technique in the field <strong>of</strong> rock engineering since it has the po¬tential to be used for the collection <strong>of</strong> data required for several routine tasks. However, it is essential toselect the most appropriate laser scanner according to project-specific constraints such as range, excava¬tion geometry, time available for scanning as well as point accuracy <strong>and</strong> point density. The Imager5003 <strong>of</strong>Zoller+Frohlich was used in an experimental tunnel in the Mont Terri Rock Laboratory for the characteriza¬tion <strong>of</strong> geological discontinuities <strong>and</strong> displacement monitoring. This scanner was found to be particularlywell-suited for rock mass characterization in underground excavations while yielding an accuracy<strong>of</strong> lessthan 1 cm in the determination <strong>of</strong> the displacement <strong>of</strong> object points. Nevertheless, preliminary results sug¬gested that displacement maps with a higher order <strong>of</strong> accuracy can be produced by taking advantage <strong>of</strong>the large quantity <strong>of</strong> spatial data provided bythe laser scanner.displacement maps would greatly improve the underst<strong>and</strong>ingTherefore, the construction <strong>of</strong> accurate<strong>of</strong> the rock mass behaviour. Crucial issuesidentified for this application included referencing to a stable reference system, coordinate transformation,noise reduction <strong>and</strong> smoothing <strong>of</strong> point clouds.Regarding rock mass characterization, efforts should be made to automate the recognitionities so that the time required for data analysis can be significantly<strong>of</strong> discontinu¬decreased. Future work will focus onthe development <strong>and</strong> comparison <strong>of</strong> processing algorithms to improve the accuracy <strong>of</strong> the displacementmapping. The resulting maps will be further compared with the results <strong>of</strong> other field investigation meth-