Alessandro Gallo

A comparative analysis between active and passive techniques for underwater 3D reconstruction of close-range objects.

In some application fields, such as underwater archaeology or marine biology, there is the need to collect three-dimensional, close-range data from objects that cannot be removed from their site. In particular, 3D imaging techniques are widely employed for close-range acquisitions in underwater environment. In this work we have compared in water two 3D imaging techniques based on active and passive approaches, respectively, and whole-field acquisition. The comparison is performed under poor visibility conditions, produced in the laboratory by suspending different quantities of clay in a water tank. For a fair comparison, a stereo configuration has been adopted for both the techniques, using the same setup, working distance, calibration, and objects. At the moment, the proposed setup is not suitable for real world applications, but it allowed us to conduct a preliminary analysis on the performances of the two techniques and to understand their capability to acquire 3D points in presence of turbidity. The performances have been evaluated in terms of accuracy and density of the acquired 3D points. Our results can be used as a reference for further comparisons in the analysis of other 3D techniques and algorithms.

3D documentation and monitoring of the experimental cleaning operations in the underwater archaeological site of Baia (Italy)

The CoMAS project aims to develop new methodologies and tools for the restoration and conservation of submerged archaeological artefacts. One of the project goals is to study the cleaning operations that are intended to remove the living organisms (algae, sponges, molluscs, etc.). These organisms cause severe deteriorations of the artefacts and their removal is crucial for the subsequent phases of consolidation and protection. In particular, the Unit of Underwater Archaeology of the Istituto Superiore per la Conservazione ed il Restauro is experimenting and comparing different cleaning techniques and tools developed in the context of the CoMAS project. This comparison requires also a precise documentation of the test cases and a quantitative measurement of the effectiveness of the cleaning procedures. This paper describes the process that has been defined in order to document and monitor the results obtained through different cleaning experiments, conducted with different tools and utensils over various types of surfaces (marble, bricks, mortar, etc.) affected by several types of biological colonization. The process includes: 1) the 3D mapping of the experimental site; 2) the planning of the tests and the choice of the areas to be cleaned; 3) the 3D reconstruction of the selected areas; 4) the execution of cleaning operations; 5) the 3D acquisition of the cleaned areas; 6) the comparison of the 3D model of the areas before and after the cleaning; 7) the analysis of the data about the cleaning effectiveness. This process has been implemented during an experimentation carried out in the “Villa dei Pisoni”, located within the underwater archaeological site of Baia near Naples.

Multi-view 3D reconstruction of small stone samples deteriorated by Marine organisms

The diagnostic analysis of decay processes on small specimens is gaining importance in the restoration and maintenance of archeological finds. In this context, the 3D reconstruction is very useful for the study and identification of the different types of decay. In this paper we present the analysis conducted on two small specimens taken from an ancient underwater pavement, using a new technique for the 3D reconstruction of small sized objects based on a multi-view passive stereo technique applied on a sequence of macro images. In order to overcome the problems related to the use of macro lenses, such as the very small depth of field and the loss of sharpness due to diffraction, each image of the sequence is obtained by merging a stack of images acquired at different focus planes by the means of an image fusion algorithm. The experimentation involves a series of preliminary laboratory tests in which we validate the system accuracy and the 3D reconstruction of specimens taken from a marble pavement located in the underwater archeological site park of Baiae (Naples, Italy). The results show that with our approach it is possible to obtain high quality textured 3D models of objects with dimensions ranging from few millimeters to few centimeters, which can be usable both for interactive measurements and virtual presentations.

Design of an electric tool for underwater archaeological restoration based on a user centred approach

This paper describes a part of the contribution of the CoMAS project (“In situ conservation planning of Underwater Archaeological Artifacts”), funded by the Italian Ministry of Education, Universities and Research (MIUR), and run by a partnership of private companies and public research centers. The CoMAS project aims at the development of new materials, techniques and tools for the documentation, conservation and restoration of underwater archaeological sites in their natural environment. This paper details the results achieved during the project in the development of an innovative electric tool, which can efficiently support the restorers’ work in their activities aimed to preserve the underwater cultural heritage in its original location on the seafloor. In particular, the paper describes the different steps to develop an underwater electric cleaning brush, which is able to perform a first rough cleaning of the submerged archaeological structures by removing the loose deposits and the various marine organisms that reside on their surface. The peculiarity of this work consists in a user centred design approach that tries to overcome the lack of detailed users’ requirements and the lack of norms and guidelines for the ergonomic assessment of such kind of underwater tools. The proposed approach makes a wide use of additive manufacturing techniques for the realization and modification of prototypes to be employed for in-situ experimentation conducted with the final users. The user tests have been addressed to collect data for supporting the iterative development of the prototype.

DISEÑO Y CONSTRUCCIÓN DE UN CINCEL ELÉCTRICO PARA APLICACIONES SUBMARINAS

La arqueologia subacuatica se esta convirtiendo en un campo determinado de estudio e investigacion en patrimonio cultural, gracias a la mejora de materiales, tecnologias y metodologias de exploracion. El objetivo de la arqueologia subacuatica es mejorar y preservar los artefactos sumergidos sin extraerlos de los fondos marinos. Este documento describe las etapas de diseno y fabricacion de un cincel submarino electrico