habitat rupestre.pdf - Società Friulana di Archeologia

M. Pasquinienous light without, however, having to place numerous lightsources in the room, which would “dirty” the point cloud, wecan also use, for example, a light system that is connected directlyto the camera. (Fig. 2)The fact that identifying geometrical points in rupestrianspaces is difficult effects not only the choice of tools, but alsothe working process that needs to be carried out during a 3Dlaser scanning surveying session.The fact that during the registration of squired data it is necessaryto provide the software with precise and identifiablepoints of contact in the partial clouds taken from different scanpositions makes it necessary for the operator to prepare, in thescanning phase, the exact position of each target. 2 (Fig. 3)It is inconceivable, in fact, in the case of rupestrian architecture,that partial point clouds can be overlapped by choosingthe morphological points of contact on the point cloud at theend: this would, in effect, result in a loss of metric reliability.Time efficiency during the surveying process cannot, in ouropinion, be justified when the quality of the final product iscompromised.Therefore underground architectural surveying, includingdigital ones, must be accompanied by a series of precise solutions,which in other cases can, sometimes, be ignored byopting for simpler and faster operations.A recent experiment conducted during the survey of a sort ofunderground burial ground 3 underlined the need, in certainconditions, to experiment methods that are normally not takeninto consideration in this field. In the aforementioned case,they went on, for example, to scan the area with an up-sidedownscanner in order to acquire the points while avoidingthe problem of the characteristic circular ‘clouded zone’ abovethe scanner, so as to produce a correct ‘coverage’ of concavestructures that are otherwise difficult to reach. (Fig. 4)Another problem we must take into consideration when conductingan automatic survey of buried structures is the absoluteneed for a topographic base on which to register a correctoverlapping of the individual point clouds.In the case in which the areas to be surveyed are narrow andlong or built in succession with a single point of access to theoutside, the overlapping of the scans, even with the use of preciselyprepared targets, may lead to globally unacceptable errors(this can happen, for example, when it is impossible todoesn’t align the targets).Fig. 5 Use of a detailed 3d model to produce, during the post-production,plan and section drawings and prospectic cutaway.The possibility of bi-dimensional and tri-dimensional restitutionThe use of digital equipment, as well as making the measuringprocess faster and more reliable, allows the surveyor to putoff choices, which are otherwise binding in the first phase ofthe operation, until the time of restitution; an example is thatof the sectional planes (for plans and vertical sections) withwhich space can be represented. (Fig. 5)This allows us to overcome the problems described in thecourse of a traditional survey in rupestrian sites, which do notend with the measuring phase, but also have an effect on thegraphical restitution phase, the results of which are amplified.The arbitrariness of the choice of points to be measured istherefore solved prior, with the additional advantage of beingable to choose the level of detail of the individual scans basedon the objectives and the aim of the work in its totality.177volumeRicerca_OK_2012-11-15.indd 177 16/11/2012 15:03:07