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

88 5. Kinematic Laser Scanningmirror about one axis. The missing third dimension is generated by the motion of the scanner bya test trolley.means ofThe following sections discuss the key elements that are necessary to perform kinematic applications. First,the test trolley, the calibration track line and the characteristics and particularities of the test laboratory aredescribed. Second, the laser scanner is investigated regarding the determination of a rotation time that maydefine a time tag. The third part involves the total station, which determines the position of the moving testtrolleyon the calibration track line. Thefocus is on the processing of the acquired data with the purposeof using this data for kinematic applications. Last, someaspects regarding the synchronization of the data,which were acquired by the two instruments, the laser scanner and the total station, are discussed.Although the data acquisition and registration processes differ for static laser scanning applications andkinematic laser scanning applications, data processing and modeling and visualization aspectsare similar.Thus, the remarks of Chapter 4 regarding these aspects are also applicable for kinematic laser scanning.5.1 Test Trolley on Calibration Track LineThe laser scanner is mounted on the test trolley, which moves alongthe calibration track line. The laserscanneroperates in the profiler mode. This means the laser beam only rotates in a 2D plane. The resultingcoordinates, regarding the relative local scanner system, are only2D coordinates. Theas well as the missing third dimension for 3D coordinates, have to be acquired byabsolute position,additional sensors. Thethird dimension is generated by an automated total station, which is tracking the moving test trolley.use of a total station also allows for the inclusion of the 3D coordinates in an absolute reference system.TheSurveying in kinematic applications requires not only the position of the moving trolley in 3D coordinates,but also additional information on the orientation of the test trolley. The latter is essential since varyingorientations of the trolley lead to variations in the local reference system. The orientation can be describedby three attitude angles, which define the orientation of the local system with respect to the absolute system.In summary, the information required to generate 3D point clouds, which are acquired by the moving laserscanner, in an absolute coordinate system are:• position vectors of the point cloud in the local scanner system x\• rotation matrices described by three attitude anglesthat define the orientation of the local scannersystem with respect to the absolute coordinate system• position vectors of the moving local scanner system with respect to the absolute coordinate systemxa.Mathematically, the position vectors for the point cloud with respect to the absolute reference system canbe calculated byp = xa + R- xi. (5.1)The rotation matrix R influences the position vectors p such that with growingdistances from the laserscanner, an erroneous rotation increases errors in the position of the points.This is known as the lever armeffect. The shorter the object range, the less the position error. In addition, the translation vector xa onlycauses a constant shift of all the points.each point.The setup for kinematic laser scanning is shown in FigureThus, an erroneous translation vector has the same influence on5.1. The laser scanner is mounted on the testtrolley and is equipped with a prism on top of the laser scanner. The trolley moves alongthe track line and