Laser Scanning and close range photogrammetry: Towards a single measuringtool dedicated to architecture and archaeology.

In this research we began to develop a software tool for survey of the artistic and architectural heritage that combines the techniques of the laser scanning and photogrammetry, suitable to specific cases of architecture and archaeology. The fundamental idea of the project is in the existence of a previous model of surveyed object (base of knowledge), model that will serve for elaborating a geometric and theoretical description, devoted, on one side, to drive the process of measure, (laser scanning or photogrammetry), and, from the other, to define a complete representation of the object, where the measures and the architectural hypotheses coexist (expert system). Our target is to experiment a method of survey speditive and integrated, according to different techniques, that acquires information on architectural objects on which exists an emergency due to external factors (environmental degrade or pollution, catastrophic events as landslides or earthquakes, war events), or there is the impossibility of an enjoyable access (excavations on various overlapped layers, sites of difficulty access or underwater). The method of search articulates in three phases: A. The laser scanning that allows to model objects in the three dimensions with a frequency of measurements that could not be acquired in the same time with the traditional methods. The software, used for the data management acquired by the series of information coming from the laser, creates a 3D triangular model (mesh) on which applies textures with bidimensional information necessary to get the final result. The laser scanning generally asks for the survey of an object from different angle to analyse the parts in shade or hidden, but it is not always easy to put opportunely the laser sensor in the most appropriate point. B. We have developed an analogous approach in photogrammetry: using some photos shouted without too many references, it is possible to integrate the parts in shade or lacking, coming from the laser scanning. A survey based on the approximate geometry of the object and on the ?autocorrelation? allows to get automatically an ?irregular mesh? with an appropriate structure. The orientation phase uses the data furnished by the scanner to direct the photogrammetric measurements in the same axial system of reference. C. The last phase uses an ?expert system? based on the knowledge of the representation of the object measured with the purpose to reconstruct a architectural or archaeological object based on the real measures and on the theoretical model in collaboration with architects or with archaeologists. The object on which such method is experimented is an Etruscan amphora recovered in the wreck of the Grand Ribaud F, near Hyeres, France, and studied by Doctor Luc Long, administrator of the cultural heritage of the DRASSM of Marseille, France. The principal objective of the survey of the artistic and architectural patrimony is to furnish a precise documentation of status quo of surveyed objects (monuments, buildings, objects and archaeological sites) for their maintenance and protection as base for scientific and restoration studies as well as for the presentation to the public. The survey of complexes architectural or archaeological objects, not planar or with mouldings and decorative elements, asks for high-density spatial and high resolution data, that can be produced by new techniques combined of laser scanning and photogrammetry. -