Michele Russo

A Multi-Resolution Methodology for the 3D Modeling of Large and Complex Archeological Areas

This article reports on a multi-resolution and multi-sensor approach developed for the accurate and detailed 3D modeling of the entire Roman Forum in Pompei, Italy. The archaeological area, approximately 150 × 80 m, contains more than 350 finds spread all over the forum as well as larger mural structures of previous buildings and temples. The interdisciplinary 3D modeling work consists of a multi-scale image- and range-based digital documentation method developed to fulfill all the surveying and archaeological needs and exploit all the intrinsic potentialities of the actual 3D modeling techniques. The data resolution spans from a few decimeters down to few millimeters. The employed surveying methodologies have pros and cons which will be addressed and discussed. The results of the integration of the different 3D data in seamlessly textured 3D model are finally presented and discussed.

Performance Evaluation of Triangulation Based Range Sensors

The performance of 2D digital imaging systems depends on several factors related with both optical and electronic processing. These concepts have originated standards, which have been conceived for photographic equipment and bi-dimensional scanning systems, and which have been aimed at estimating different parameters such as resolution, noise or dynamic range. Conversely, no standard test protocols currently exist for evaluating the corresponding performances of 3D imaging systems such as laser scanners or pattern projection range cameras. This paper is focused on investigating experimental processes for evaluating some critical parameters of 3D equipment, by extending the concepts defined by the ISO standards to the 3D domain. The experimental part of this work concerns the characterization of different range sensors through the extraction of their resolution, accuracy and uncertainty from sets of 3D data acquisitions of specifically designed test objects whose geometrical characteristics are known in advance. The major objective of this contribution is to suggest an easy characterization process for generating a reliable comparison between the performances of different range sensors and to check if a specific piece of equipment is compliant with the expected characteristics.

Massive 3D Digitization of Museum Contents

The goal of the 3D-ICONS European Project is to provide EUROPEANA (www.europeana.eu) with accurate 3D models of architectural and archaeological monuments and buildings of remarkable cultural importance. The purpose of this paper is to describe the specific processing pipeline that has been set for digitizing a significant part of the Civic Archaeological Museum in Milan (Italy). All the technical and logistic aspects needed for capturing 3D models in a Museum environment, the implication with IPR, and the metadata acquisition, are covered. The main issue is generating a good result by the technical point of view, minimizing the impact on the usual Museum activity during the 3D capturing operations, shortening in the meantime the processing time to the minimal allowed by the different applicable techniques. This condition has led different choices related to the survey technologies (laser scanning and image based modeling) and the related data processing. Both technical and descriptive metadata have been collected for each item acquired, for generating a record of data searchable on EUROPEANA, with the addition of new metadata not defined in the minimal record, for making traceable the path leading to the generated digital content. The paper gives a general discussion of such issues with some specific examples referred to the large set of 3D objects digitized within the 3D-ICONS project.

Range sensors on marble surfaces: quantitative evaluation of artifacts

While 3D imaging systems are widely available and used, clear statements about the possible influence of material properties over the acquired geometrical data are still rather few. In particular a material very often used in Cultural Heritage is marble, known to give geometrical errors with range sensor technologies and whose entity reported in the literature seems to vary considerably in the different works. In this article a deep investigation with different types of active range sensors used on four types of marble surfaces, has been performed. Two triangulation-based active sensors employing laser stripe and white light pattern projection respectively, and one PW-TOF laser scanner have been used in the experimentation. The analysis gave rather different results for the two categories of instruments. A negligible light penetration came out from the triangulation-based equipment (below 50 microns with the laser stripe and even less with the pattern projection device), while with the TOF system this came out to be two orders of magnitude larger, quantitatively evidencing a source of systematic errors that any surveyor engaged in 3D scanning of Cultural Heritage sites and objects should take into account and correct.

A multidisciplinary approach to 3D survey and reconstruction of historical buildings

The aim of this research is to suggest a methodology based on 3D survey and reconstructive modeling, suitable to increase the actual knowledge of an historical building and supporting its historical interpretation. The case study used for testing the proposed methodology is the huge Chartreuse of Pavia, with a special focus on a relatively unexplored portion of the monument. The survey, based on 3D laser scanning and orthoimages, integrated by historical studies and other complementary information (thermoluminescence dating, IR imaging, hystorical analysis), allowed to read all the architectural aspects hidden in this highly architecturally stratified monument, improving in this way the comprehension of the buildings transformations in time. A 3D reconstruction approach was then suggested, merging several information of different nature, from the actual geometry of the building to the interpretation of historical documents, suggesting a sequence of diachronic models as virtual narration of the historical evolution. On other hand the 3D models were used to obtain a cross-validation of the historical evolution hypotheses developed by experts in the various disciplines involved in the project. The data collected were exploited through a web portal in order to enhance the readability of tangible and intangible heritage associated to that Chartreuse portion, nowadays not accessible to common public.

Multi-scalar 3D digitization of Cultural Heritage using a low-cost integrated approach

In the architectural survey field, one of the main aspects to consider during a 3D digitization is the multi-scalar geometrical complexity of the artifact to acquire, besides other fundamental factors connected with the different aims of communication. Since the widespread of range-sensors has provided extremely versatile instruments able to easily acquire huge amount of data that can be processed for different uses and users and changing communication aims, the possibility to survey and restore high-quality 3D multi-resolution models has become an urgent need. Despite these developments, these technologies are still very expensive, need expertise and present persistent bottlenecks both in the reverse modeling process and in time consuming. In order to overcome these critical aspects and taking advantage of recent improvements of automated image-based technologies based on the Structure from Motion approach, this contribution presents some first results of investigations on the reliability of these low-cost technologies for the 3D digitization of Cultural Heritage. One of the main aims of these investigations rely on developing a procedure that could ease the work of surveyors called to represent artifacts at an architectural scale using fast and low-cost technologies. 3D models derived using the selected low-cost image-based technologies were compared among each other and with a 3D laser scanner gold standard acquisition. These investigations led to qualitative and quantitative evaluations and to considerations on times and skills required by all tested technologies. Strengths and weaknesses are highlighted, suggesting the best solution with respect to the optimization of all considered aspects. Finally, integration of different technologies are presented, as it represents the best solution in multi-scalar contexts.

Low cost characterization of TOF range sensors resolution

The core of the paper is focused on the experimental characterization of four different 3D laser scanners based on Time of Flight principle, through the extraction of resolution, accuracy and uncertainty parameters from specifically designed 3D test objects. The testing process leads to four results: z-uncertainty, xy-resolution z-resolution and z-accuracy. The first is obtained by the evaluation of random residuals from the 3D capture of a planar target, the second from the scanner response to an abrupt z-jump, and the last two from direct evaluation of the image extracted by different geometric features progressively closer each other. The aim of this research is to suggest a low cost characterization process, mainly based on calibrated test object easy to duplicate, that allow an objective and reliable comparison between 3D TOF scanner performances.

3D digitizing a whole museum: A metadata centered workflow

Massive 3D digitization has never been attempted before as in the framework of the 3D-ICONS European project, whose purpose is populating Europeana - an Internet portal for accessing to millions of books, paintings, films and archival records that have been digitized throughout Europe - with at least 3000 3D models of important archaeological and artistic objects. A correspondingly high number of metadata associated to the 3D models has to be managed and supplied to Europeana in order to make usable the whole set of 3D models generated within the project. This paper presents a possible workflow that allows to collect in advance all the metadata needed for the following Europeana publication phase; assign coherent and univocal IDs to the digitized objects; track the work progress adding technical metadata to the descriptive ones at the digitization stage.

A virtual connection between past and present: The digital revival of Cham's Architecture (Vietnam)

The traditional approach for understanding an archaeological site, mainly focused on excavations and stratigraphic examination of findings through the archaeological analysis, is still the main way for hypothesizing its most probable interpretation. As demonstrated in several case studies 3D digital acquisition techniques may greatly help for applications such as site and findings documentation, digital stratigraphy, 3D GIS or virtual interaction between experts. In addition, an accurate geometrical representation in digital form may be used, once integrated by archaeological considerations, as a starting point for creating virtual reconstructions of the site, embedding the most probable hypotheses. However, this last step might be critical for a apparently trivial reason: with very few exceptions the archaeological skill for interpreting some ruins and the technological skill for 3D modeling the corresponding site reconstruction are owned by different individuals or group of scholars. The aim of this paper is to describe a widespread 3D documentation of a site and a possible reconstruction process step by step, starting from a laser scan survey and a set of historical documents, focusing on a reasonable multi-disciplinary concurrent interaction to reach the best virtual reconstruction solutions. This path may help both archaeologists to better focus their thoughts through a detailed visual representation, and the technological experts to avoid misleading details in the final virtual reconstruction. The case study regards a group of Cham temples located in the My Son site, an UNESCO archeological area in Vietnam.