Range data are acquired separately from the outer and inner side of the walls. Two single laser
scanner stations are used at a mean distance of 25 m from the wall surface. The TLS is not set up
over a known point, so the position and orientation of the TLS is determined by resection from the
reference coordinate system defined by high precision topography. Additionally, taking into
account that the GX200 incorporates an automatic dual axis compensator, the TLS is carefully
levelled each time in order to define the vertical direction, providing a geometric constraint to
check the vertical direction of the reference coordinate system. While the resection process will
serve as an additional error source, it is a practical task to enable direct comparisons of vertical
directions from the topography and TLS data sources.