Terrestrial laser scanner data processing

The introduction of new terrestrial laser scanner devices in the survey field has increased the possibility of more accurate and complete 3D models of the acquired objects to be obtained. This happens, above all, in the architectural and archaeological survey field in which the shape of an object is usually remarkably complex. Acquisition with laser scanner devices is, in addition, very fast and cheap and the 3D models that are obtained are very useful for users. However, particular attention must be paid during the analysis, the processing and the modelling phases of the laser scanner data. The acquired data are often characterized by the presence of elevated noise (usually gross errors and outliers) which must be removed with ad hoc techniques before starting with the manipulation of the data. Usually architectural and archaeological objects have a very complex shape and one scan is not enough to obtain the complete description of the object. In these cases, in order to eliminate the shaded areas, two or more scans must be taken from different points of view of the same object. To obtain the final 3D model of the object it is therefore necessary to align and to georefer the single scans using suitable registration techniques. In addition, when it is necessary to align a large series of scans, the use of triangulation algorithms represents the only way to avoid distortions of the 3D model, in complete analogy with the case of long single strips in photogrammetry. All these aspects have been considered and a specific software that is able to correctly process terrestrial laser scanner data has been developed by the authors. The paper presents the algorithms and the solutions adopted in order to prepare the laser scanner data to th