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 ...
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3<strong>Calibration</strong> <strong>of</strong> <strong>Terrestrial</strong> <strong>Laser</strong> <strong>Scanner</strong>The conception <strong>of</strong> an instrument assumes specific constraints between the different components.Due tomechanical imperfections, it is impossible to design an instrument exactly to theoretical planning. Thereare discrepancies between the real instrument <strong>and</strong> the ideal instrument, <strong>and</strong> these are called instrumentalerrors. The knowledge <strong>of</strong> instrumental errors is essential in acquiringreliable measurements. The moreone is aware <strong>of</strong> the systematic errors, the better one is able to correct for the real instrument with respectto its ideal construction by applying mathematical models. However, these mathematical models requireprecise knowledge <strong>of</strong> the instrument <strong>and</strong> its components. Furthermore, the calibration <strong>of</strong> an instrumentnecessitates the stability <strong>and</strong> the time constance <strong>of</strong> the calibration parameters. If these requirementsfulfilled, calibration is nearly impossible.are not<strong>Calibration</strong> <strong>of</strong> <strong>Terrestrial</strong> <strong>Laser</strong> <strong>Scanner</strong>sComponent <strong>Calibration</strong>System <strong>Calibration</strong>Distance Measurement Systemcorrection modelsAngle Measurement SystemInstrumental ErrorsNon-Instrumental ErrorsXknowledge-basednonknowledge-basedetc.Figure 3.1: <strong>Calibration</strong> <strong>of</strong> terrestrial laser scanners, categorized by component calibration <strong>and</strong> system calibration.Normally, a distinction can be made between a system calibration <strong>and</strong> a component calibration [Hennés<strong>and</strong> Ingens<strong>and</strong>, 2000]. Figure 3.1 shows the calibration procedures. The systema mathematical model or a correction function, without knowledge <strong>of</strong> each singlecalibration derives eitherinstrumental error <strong>and</strong>its influence, by appropriate observation <strong>of</strong> control points or known objects, e.g. spheres, planes.ponent calibration is mostly based on knowledge-based modeling<strong>of</strong> the instrument <strong>and</strong> its instrumentalerrors. Each single error is investigated separately in a specific experimental setup.applied to the laser scanner, Imager 5003 <strong>of</strong> Zoller+Fröhlich, cf. Table 3.1.The com¬The latter has beenBefore starting with the discussion <strong>of</strong> the calibration procedures applied on the laser scanner, some terms<strong>and</strong> definitions need to be clarified.There is <strong>of</strong>ten a misunderst<strong>and</strong>ing between calibration, performanceassessment/evaluation, <strong>and</strong> certification. They are similar in meaning <strong>and</strong> are <strong>of</strong>ten used synonymously[NIST, 2002]. However, there are slight differences in the nuances <strong>of</strong> these terms. One formal definition <strong>of</strong>calibration is given by [VIM, 1993]: