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

3.4 Instrumental Errors 51values of 0.2 mm and 0.3 mm, respectively. Thus, this deviation between the real and ideal center points isnearly in the same order as the precision, i.e. standard deviation, of the ideal offset. In summary,rotation center fits the ideal rotation center.the real14 98of the local scandatapoints14 97-adjusting cirlcecentre point (real)centre point (ideal)14 9614 9514 94£.14 9314 9214 9114 9014 89776 7 77 7 78 7 79 7 80 7 81 7 82 7 83 7 84 7 85 7 86y[m]Figure 3.26: Adjusting circle: The rotation center of the laser scanner fits to the ideal center and the data points fit tothe adjusting circle.Eccentricityof Scan CenterThe real physicalcenter of an instrument has to coincide to its idealcenter, otherwise offset parametershave to be taken into account. Disregarding this concept leads to an eccentricity of the real center, whichcauses a constant offset.Considering that the laser scanner captures the 3D environment, the eccentricityof the scan center has to be determined in three directions: x, y and z.Knowing the eccentricity easesthe use of the laser scanner for repeated measurements because this sensor can be used analogous to atotal station.Contrarily if the eccentricity is not known or not determinable, the laser scanner has to beoriented completely in 3D during the measurement procedure. Normally, this is the common practice inlaser scanning.However, there are some applications for which the knowledge of the eccentricity of thescan center is of advantage. In such applications, in-situ calibration is rarely possible and the eccentricity isof importance, e.g. deformation measurements, profile measurements of tunnels, scanningdefined by a lack of space. Thus, the knowledge of the eccentricity is not essential but helpful.The eccentricity of the scan center can be defined by three parameters: a vertical offset in heighthorizontal offsets. The vertical offset is defined by the heightof environmentsand twodifference between the internal scan centerand the center of reference and the horizontal offsets are defined by the two horizontal differences betweenthe internal scan center and the center of reference. The center of reference is represented by a well-knowncontrol point on which the laser scanner can be mounted.The calibration of the eccentricity was performed by means of a 3D coordinate transformation (six para¬meter transformation without a scale factor).The laser scanner was set up on a control point defining thecenter of reference.Several surrounding control points represented by sphereswere scanned. The centerpoints of the spheres were calculated by an adjustment procedure using the 'fix' adjustment.derived center points of the spheres and the position of the laser scanner as the originBased on the