Review and Comparison of Techniques for Terrestrial 3d-view Georeferencing

In the paper a presentation of existing georeferencing technique and a comparison between them is given. This is based on general considerations as well as on results two test applications carried out in the university laboratory, and at the ancient church of San Pietro al Monte in Civate (Lombardia, Italy). Two main ground constraints are currently used for the cultural heritage laser scanning survey: the use of targets as Ground Control Points, and the Direct Georeferencing approach, based on fixing the instrument position and attitude derived by external information (stationing over known points, levelling, azimuth orientation, use of INS/GPS in case of open and wide settlements). Moreover, nowadays several instruments can be used themselves as a total station to directly determine the stand-points coordinates as well. Both techniques can be adopted in a separate way, but they can be also integrated. The selection of a specific solution will depend upon the required accuracy for georeferencing, but can be driven also by special operational needs (available time, number of people involved, difficulty to get the site). On the other hand, an alternative solution to compute scan registration with a minimum ground control is given by the surface matching algorithms.