A terrestrial 3D laser scanner: accuracy tests

used for surveying, documentation and solid modeling of three-dimensional monuments, sites and scenes. One of these systems is the Cyrax 2400, which is of great interest because of its rapidity of scanning and creation of 3D models (1000 points/sec. – range 1.5 to 100 m). However, it is important to assess the accuracy of the models obtained with this and similar instruments, especially in the measurement of complex 3D objects. Some recent measurements with the Cyrax system have allowed us to perform the tests presented in this paper. The measured object was an historic building (XV century) near the city of Ferrara (Italy). We studied the accuracy achieved in the positioning of natural points and targets situated on parts of the building. The 3D positioning of these points and targets were carried out with different object-scanner distances (from 5 to 100 m) and with different inclinations of the laser impulses; the aim was to systematically evaluate the parameters determining the measurement accuracy of the laser scanner. To perform these assessments, the targets and natural points were also measured with traditional high-accuracy topographic instrumentation. The results of the Cyrax measurement were then compared with those of the topographic measurement