Paolo Pingi

A low cost 3D scanner based on structured light

Automatic 3D acquisition devices (often called 3D scanners) allow to build highly accurate models of real 3D objects in a cost‐ and time‐effective manner. We have experimented this technology in a particular application context: the acquisition of Cultural Heritage artefacts. Specific needs of this domain are: medium‐high accuracy, easy of use, affordable cost of the scanning device, self‐registered acquisition of shape and color data, and finally operational safety for both the operator and the scanned artefacts. According to these requirements, we designed a low‐cost 3D scanner based on structured light which adopts a new, versatile colored stripe pattern approach. We present the scanner architecture, the software technologies adopted, and the first results of its use in a project regarding the 3D acquisition of an archeological statue.

Visualization and 3D data processing in the David restoration

The program of scientific investigations planned in the framework of the restoration of Michelangelos David produced several useful guidelines for defining and developing innovative ways to process and visualize 3D data in cultural heritage applications. Our ultimate goal was to include 3D graphics among the tools which can help restorers select the proper restoration procedures for the task at hand and objectively assess restoration results. For this, the David restoration was an ideal test bed to demonstrate the usefulness of digital 3D models and visualization tools in a restoration project. Because a complex set of scientific investigations was planned before and after the restoration intervention, we could try various methodologies to support restorers and scientists with visualization tools based on 3D digital models.

VCLab''s tools for 3D range data processing

Post-processing of 3D scanned data is still the bottleneck for a wider diffusion of this technology. In this paper we describe our second generation tools for processing 3D scanned data. In particular, our tools support: range maps alignment, range maps merge (or fusion), mesh simplification and color attribute management. This software package has been implemented by scratch and encompasses both up-to-date solutions and some original methods (merging, simplification, color management and, in part, alignment). The paper presents the architecture of the tools, the features supported and algorithms used; finally, an evaluation of its use in the framework of a complex acquisition in the Cultural Heritage domain (3D scanning of a bronze statue) is reported.

The Marching Intersections algorithm for merging range images

AbstractA new algorithm for the integration of partially overlapping range images into a triangular mesh is presented. The algorithm consists of three main steps: it locates the intersections between the range surfaces and a reference grid chosen by the user, then merges all nearly coincident and redundant intersections according to a proximity criterion, and, finally, reconstructs the merged surface(s) from the filtered intersection set. Compared with previous methods, which adopt a volumetric approach, our algorithm shows lower computational costs and improves the accuracy of the surfaces produced. It takes into account the quality of the input measurements and is able to patch small holes corresponding to the parts of the 3D scanned object that were not observed by the acquisition device. The algorithm has been tested on several datasets of range maps; graphical and numeric results are reported.

Marching intersections: an efficient resampling algorithm for surface management

The paper presents a simple and efficient algorithm for the removal of small topological inconsistencies and high frequency details from surface models. The method, called marching intersections (MI), adopts a volumetric approach and acts as a resampling filter. All the intersection points between the input model and the lines of a user selected 3D reference grid are located and then, beginning from these intersections, an output surface is reconstructed. MI, which presents good characteristics in terms of efficiency, compactness, and quality of the output models, can be also used: for the conversion between different representation schemes; to perform logical operations on geometric models; for the topological simplification of surfaces; and for the simplification of huge meshes, i.e. meshes too large to be allocated in main memory during the simplification process. All these aspects are discussed in the paper and timing and graphic results are presented.

Exploiting the scanning sequence for automatic registration of large sets of range maps

Range map registration is still the most time consuming phase in the processing of 3D scanning data. This is because real scanning sets are composed of hundreds of range maps and their registration is still partially manual. We propose a new method to manage complex scan sets acquired by following a regular scanner pose pattern. Our goal is to define an initial adjacency graph by coarsely aligning couples of range maps that we know are partially overlapping thanks to the adopted scanning strategy. For a pair of partially overlapping range maps, our iterative solution locates pairs of correspondent vertices through the computation of a regular n×n kernel which takes into account vertex normals and is defined in the 2D space of the range map (represented in implicit 2D format rather than as a triangle mesh in 3D space). The shape-characterization kernel and the metrics defined give a sufficiently accurate shape matching, which has been proven to fit well the requirements of automatic registration. This initial set of adjacency arcs can then be augmented by the automatic identification of the other significant arcs, by adopting a criterion based on approximate range map overlap computation. With respect to the solutions present in literature, the simplifications and assumptions adopted make our solution specifically oriented to complex 3D scanning campaigns (hundreds of range maps). The proposed method can coarsely register range maps in parallel with the acquisition activity and this is a valuable help in assessing on site the completeness of the sampling of large objects.

Digital reconstruction of the Arrigo VII funerary complex

The results of a project aimed to the study, reconstruction and presentation to the public of a monument disassembled and dispersed, the mausoleum of the emperor Arrigo VII, are presented here. We used modern 3D graphics for the acquisition of accurate digital models of all the elements of the funerary complex, to draw hypothesis on its original architecture, and finally to present all this knowledge to the museum public. Issues emerged during 3D scanning are discussed. The multimedia museum presentation was implemented with an interactive visualization system, which was extended to manage standard multimedia data together with 3D geometry.

Digital representation and multimodal presentation of archeological graffiti at Pompei

Graffiti is a special form of art which gives us important knowledge on culture and social life of a lost civilization. Unfortunately, they are usually engraved on soft and non durable materials. The project described here originated from the request for a new approach to the preservation, study and ubiquitous access to Pompeis graffiti. A multidisciplinary team was setup to design a new methodology to support the digital acquisition, the study and the presentation to the public of this peculiar type of Cultural Heritage. We have investigated the use of 3D scanning technologies and graphics modelling to produce accurate digital reconstructions and to enhance them for an improved readability. The specific issues have been considered and ad hoc solutions have been devised. In terms of presentation, we have provided both visual media (interactive visualization) and physical reproduction, obtained by adopting modern rapid reproduction techniques. The work described is a sort of preliminary feasibility study: we are now planning to apply this methodology on a much wider scale at Pompei.

Using optically scanned 3D data in the restoration of Michelangelo's David

Modern 3D scanning technologies allow to reconstruct 3D digital representations of Cultural Heritage artifacts in a semi-automatic way, characterized by very high accuracy and wealth of details. The availability of an accurate digital representation opens several possibilities of utilization to experts (restorers, archivists, museum curators), or to ordinary people (students, museum visitors). 3D scanned data are commonly used for the production of animations, interactive visualizations, or virtual reality applications. A much more exciting opportunity is to use these data in the restoration of Cultural Heritage artworks. The integration between 3D graphic and restoration represents an open research field where many new supporting tools are required; the David restoration project has given several starting points and guidelines to the definition and development of innovative solutions. Digital 3D models can be used in two different but not subsidiary modes: as an instrument for the execution of specific investigations and as a supporting media for the archival and integration of all the restoration-related information, gathered with the different studies and analysis performed on the artwork. In this paper we present some recent work done in the framework of the Michelangelos David restoration project. A 3D model of the David was reconstructed by the Digital Michelangelo Project, using laser-based 3D scanning technology. We have developed some tools to make those data accessible and useful in the restoration. Preliminary results are reported here together with some directions for further research.

Restoring David using 3D

Refurbishing Michelangelos David has produced several useful restoration guidelines. These guidelines can help restorers select the proper procedures for the task and, objectively, assess the results. The work also has helped us develop innovative ways to process and visualize 3D data in cultural heritage projects. The David restoration was an ideal test bed. We try various methodologies to support restorers and scientists with visualization tools based on 3D digital models. 3D digital models can be a tool for undertaking specific investigations, or as supporting media for archiving and integrating the restoration-related information.