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

acquisitiondescribingFinally, thatMainly,results.applicationways. The models by linemoving base objectcompleteddifferentmathematicalaregressionposition parametersestablishesseveral dataapplied andpointsThus,aKaimancalculatingpre-processingrequiredacquired methods processingto filter.wasorientationalsoexample forced motion2TPS1201 essential.trajectoryyieldof laserrunakinematicwith trolley from scanner anearly Leica were has constant Geosystemsdescribedestimated.velocity.126 6. Applications of Terrestrial Laser Scanningtrajectory is assessed by control points with coordinates derived analogous to the procedurethe use of the regression line, cf. Section 6.3.2.described for0 105£0 100 'rtf*M MfU^M^^^^^i^^^^j*J/1WW itaiArvpfip yvwilj¥ )\vy W\f y y0 09,5,„„44004450 4500 4550 4600 4650 4700 4750time tag [s]Figure 6.15: Velocity of moving trolley estimated by Kaiman filterforone data set.For example, the velocity of the test trolley of one data set estimated by the Kaiman filter is shown in Figure6.15. It can be seen that the motion of the trolleyoscillates. These oscillations are based either on the noiseproduced by the tracking total station or by the variations of the encoders controlling the velocityof thetest trolley. Considering a distance error of As 1mm by = a time interval of At 0.1s, = a variation inthe velocityof v = 0.01 results. Thus,with the distance accuracy of the total station.the oscillations of the velocity are relatively small in comparisonThe accuracy of the trajectory and the scanned point cloudis assessed by control points. The same parameters for the data sets are chosen compared to the examplewhere the regressionline was used. Table 6.3 summarizes the results and shows the 3D accuracy for thecontrol points. The accuracy is sufficiently high since the 3D accuracy is within 5 mm. Surprisingly, theaccuracy decreases with the time and therefore, with the length of the trajectory. One possibility is thatthe equidistant time tags of the total station measurements, derived for the Kaiman filter, show deviations.Another reason can be found in the Kaiman filter. The tuning of the filter, e.g. mathematical model ofthe system state, covariance matrices, offers several ways of deriving the trajectory. Considering the givenaccuracy of the used total station2 in the tracking mode (5 mm + 2 ppm), the 3D accuracy, given in Table 6.3,fits the manufacturer's specification.Furthermore, the same conclusion, as for the regression line, can be drawn: neither the rotation time nor thescan resolution significantly influence the 3D accuracy. Only the treatment of the diameter of the spheresincreases the accuracy.shown in Table 6.3.Changing the velocity to v = 0.2— and v = 0.3— have similar results, which are6.3.4 ResultsKinematic laser scanning has become an alternative to static laser scanning. The advantage is a higherperformance of scanning objects characterized by a fast acquisition rate. For linear objects, e.g.roads, kinematic applications are especially superior to static applications.tunnels orThe accuracy that can be achieved is not only limited bythe laser scanner used. The