It is important to state that this section summarises only some of the work undertaken by a few of the members of the Task Force.
One area where terrestrial laser scanning has been accepted as a very useful tool is in cultural heritage, as it is a natural progression from photogrammetry and the two technologies do possess many similarities. Applications vary from detailed documentation and 3D modelling to close-range structural recording (eg Boehler et al. 2003a, b, Barber et al. 2002, Ioannidis & Tsakiri 2003, Tsakiri et al. 2003). On the other hand, most commercially available laser scanning systems make little attempt to integrate well into existing field survey practice, although many users such as the mining industry would benefit greatly from remote surveying tools.
A critical area of any new technology is the control check of the performance and metrological aspects of the instrumentation and field operation. Experiments to define the mechanical-optical stability of a number of instruments have indicated that the large weight of the currently available commercial laser scanners may be affecting a number of mechanical parameters such as eccentricity of axis (Ingensand et al. 2003).
The resolution and accuracy of the distance measurement provided by different types of long-range terrestrial scanners (pulse-range or frequency type) has been the subject of study of many groups. The experiments include comparison with EDM calibrated baselines (eg Boehler et al. 2003c, Licthi et al. 2000a, Gordon et al. 2001b) or laboratory tests with an interferometric calibration line (eg Ingensand et al. 2003). Most tests indicate that the range accuracy and resolution are within manufacturers' specifications.
Further to calibration analysis, the study for the establishment of suitable test sites and control facilities for laser scanner instruments is a topic under investigation (eg Iavarone & Martin 2003). It is important for the test facilities to provide adequate range and dispersion of control points in order to identify range and angular errors. Also, setting the standard practices involved in the collection and archiving of data from terrestrial laser scanners is a priority area for clients and contractors alike and there is work undertaken in this area by some members of the group (eg Barber et al. 2003).
A further advantage of the three-dimensional coordinate observations provided by the dense laser scan data sets is that these are coupled with returned laser beam intensity. They become, therefore, radiometric data, which results in extending the scanner's capability from a geometric sensor to a multi-spectral imaging system. Studies on spectral filtering and classification of the point clouds allow for more effective processing of the data in a spectral feature sense rather than being dependent on the spatial sampling resolution of a scanner (eg Licthi 2003, Lichti & Harvey 2002).
The use of terrestrial laser scanning in deformation monitoring engineering applications at first may be questioned because of the relatively large single-point precision (about 5-6mm). However, the dense data sets allow for surface-wise modelling instead of point-wise analysis and provide in this way an almost ten-fold improvement in accuracy at the resultant surface model (eg Gordon et al. 2001a). This approach has shown that the technology can be used alike in large scale deformation applications such as in dam slope monitoring (eg Lichti et al. 2000b) and in small scale studies such as in precision measurements of laboratory loading tests (eg Gordon et al. 2002, 2003a, b). By allowing the 3D representation of a structure or testing object, the analytical models representing the bending and deforming mechanisms can be developed thus enhancing the understanding of their structural mechanisms.
Benchmarking and validation of the terrestrial laser scanner data is usually performed using surveying and photogrammetric methods either in a point-wise sense or surface-wise approach. Comparison with GPS measurements (eg Lichti et al. 2000a) and photogrammetry-derived point coordinates (eg Lichti et al. 2002) has shown successful results. There is still the need to investigate rigorous methods of benchmarking the laser scanner data.
The above references are found in Bibliography for Terrestrial Laser Scanning in Deformation Monitoring