TERRESTRIAL LASER SCANNERS WITH A NARROW FIELD OF VIEW: THE EFFECT ON 3D RESECTION SOLUTIONS

Abstract

Three-dimensional (3D) resection is used to locate an unknown, occupied station in object space, given observations to three or more known, unoccupied targets. Considering the emerging technology of terrestrial laser scanning, 3D resection may be used to determine the position and orientation of a scanner head in a project coordinate system. Some scanner manufacturers have equipped their instruments with facilities to position and orient the scanner over a known point thus permitting all data collected from that location to be directly georeferenced. As a result, resection is not necessary but is optional. However, due to the hardware design path that other scanner manufacturers have pursued, their systems do not have these facilities. These laser scanning systems must use the process of 3D resection to locate the scanner in object space. Furthermore, these scanners (at the time of writing in October 2002) also possess a relatively narrow field of view (angular-wise, 40° in the vertical and 40° in the horizontal). Consequently, this restricts the placement of control targets relied upon for resection. This paper describes an investigation into the effect of control geometry on resection solutions and how errors from computed resection parameters are manifested in georeferenced scan data and measurements derived from these data. Results using simulated and real data show that the positional accuracy may be considerably worse than the (manufacturer) advertised point accuracies.