Marco Callieri

MeshLab: an Open-Source Mesh Processing Tool

The paper presents MeshLab, an open source, extensible, mesh processing system that has been developed at the Visual Computing Lab of the ISTI-CNR with the helps of tens of students. We will describe the MeshLab architecture, its main features and design objectives discussing what strategies have been used to support its development. Various examples of the practical uses of MeshLab in research and professional frameworks are reported to show the various capabilities of the presented system.

Technical Section: Masked photo blending: Mapping dense photographic data set on high-resolution sampled 3D models

The technological advance of sensors is producing an exponential size growth of the data coming from 3D scanning and digital photography. The production of digital 3D models consisting of tens or even hundreds of millions of triangles is quite easy nowadays; at the same time, using high-resolution digital cameras it is also straightforward to produce a set of pictures of the same real object totalling more than 50M pixel. The problem is how to manage all this data to produce 3D models that could fit the interactive rendering constraints. A common approach is to go for mesh parametrization and texture synthesis, but finding a parametrization for such large meshes and managing such large textures can be prohibitive. Moreover, digital photo sampling produces highly redundant data; this redundancy should be eliminated while mapping to the 3D model but, at the same time, should also be efficiently used to improve the sampled data coherence and the appearance representation accuracy. In this paper we present an approach where a multivariate blending function weights all the available pixel data with respect to geometric, topological and colorimetric criteria. The blending approach proposed is efficient, since it mostly works independently on each image, and can be easily extended to include other image quality estimators. The resulting weighted pixels are then selectively mapped on the geometry, preferably by adopting a multiresolution per-vertex encoding to make profitable use of all the data available and to avoid the texture size bottleneck. Some practical examples on complex data sets are presented.

3D Models for Cultural Heritage: Beyond Plain Visualization

Digital technologies are transforming the way cultural heritage researchers, archaeologists, and curators work by providing new ways to collaborate, record excavations, and restore artifacts.

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.

3DHOP: 3D Heritage Online Presenter

Abstract 3D Heritage Online Presenter (3DHOP) is a framework for the creation of advanced web-based visual presentations of high-resolution 3D content. 3DHOP has been designed to cope with the specific needs of the Cultural Heritage (CH) field. By using multiresolution encoding, it is able to efficiently stream high-resolution 3D models (such as the sampled models usually employed in CH applications); it provides a series of ready-to-use templates and examples tailored for the presentation of CH artifacts; it interconnects the 3D visualization with the rest of the webpage DOM, making it possible to create integrated presentations schemes (3D + multimedia). In its design and development, we paid particular attention to three factors: easiness of use, smooth learning curve and performances. Thanks to its modular nature and a declarative-like setup, it is easy to learn, configure, and customize at different levels, depending on the programming skills of the user. This allows people with different background to always obtain the required power and flexibility from the framework. 3DHOP is written in JavaScript and it is based on the SpiderGL library, which employs the WebGL subset of HTML5, implementing plugin-free 3D rendering on many web browsers. In this paper we present the capabilities and characteristics of the 3DHOP framework, using different examples based on concrete projects.

High quality PTM acquisition: reflection transformation imaging for large objects

Reflection Transformation Imaging has proved to be a powerful method to acquire and represent the 3D reflectance properties of an object, displaying them as a 2D image. Recently, Polynomial Texture Maps (PTM), which are relightable images created from a set of photos of the object taken under several different lighting conditions, have been used in Cultural Heritage field to document and virtually inspect several sets of small objects, such as cuneiform tablets and coins. In this paper we explore the possibility of producing high quality PTM of medium or large size objects. The aim is to analyze the acquisition pipeline, resolving all the issues related to the size of the object, and the conditions of acquisition. We will discuss issues regarding acquisition planning and data gathering. We also present a new tool to interactively browse high resolution PTMs. Moreover, we perform some quality assessment considerations, in order to study the degradation of quality of the PTMs respect to the number and position of lights used to acquire the PTM. The results of our acquisition system are presented with some examples of PTMs of large artifacts like a sarcophagus of 2.4 × 1 m size. PTM can be a good alternative to 3D scanning for capturing and representing certain class of objects, like bas-relieves, having lower costs in terms of acquisition equipment and data processing time.

Flow-Based Local Optimization for Image-to-Geometry Projection

The projection of a photographic data set on a 3D model is a robust and widely applicable way to acquire appearance information of an object. The first step of this procedure is the alignment of the images on the 3D model. While any reconstruction pipeline aims at avoiding misregistration by improving camera calibrations and geometry, in practice a perfect alignment cannot always be reached. Depending on the way multiple camera images are fused on the object surface, remaining misregistrations show up either as ghosting or as discontinuities at transitions from one camera view to another. In this paper we propose a method, based on the computation of Optical Flow between overlapping images, to correct the local misalignment by determining the necessary displacement. The goal is to correct the symptoms of misregistration, instead of searching for a globally consistent mapping, which might not exist. The method scales up well with the size of the data set (both photographic and geometric) and is quite independent of the characteristics of the 3D model (topology cleanliness, parametrization, density). The method is robust and can handle real world cases that have different characteristics: low level geometric details and images that lack enough features for global optimization or manual methods. It can be applied to different mapping strategies, such as texture or per-vertex attribute encoding.

Documentation and interpretation of an archeological excavation: an experience with dense stereo reconstruction tools

An archeological excavation is usually a rapidly evolving environment: several factors (weather, costs, permissions) force the work to be concentrated in a few weeks. Moreover, excavating is essentially a mono-directional operation, which constantly modifies the state of the site. Since most of the interpretation is performed in a second stage, it is necessary to collect a massive amount of documentation (images, sketches, notes, measurements). In this paper we present an experiment of monitoring of an excavation in Uppakra, South Sweden, using dense stereo matching techniques. The archeologists were trained to collect a set of images every day; the set was used to produce a 3D model depicting the state of the excavation. In this way, it was possible to obtain a reliable geometric representation of the evolution of the excavation. The obtained model were also used by the archeologists, by the means of an open-source tool, to perform a site study and interpretation stage directly on the geometric data. The results of the experimentation show that dense stereo matching can be easily integrated with the daily work of archeologists in the context of an excavation, and it can provide a valuable source of data for interpretation, archival and integration of acquired material.

Visualization methods for molecular studies on the web platform

This work presents a technical solution for the creation of visualization schemes for biological data on the web platform. The proposed technology tries to overcome the standard approach of molecular/biochemical visualization tools, which generally provide a fixed set of visualization methods. This goal is reached by exploiting the capabilities of the WebGL API and the high level objects of the SpiderGL library, these features will give the users the possibility to implement an arbitrary visualization scheme, while keeping simple the implementation process. To better explain the philosophy and capabilities of this technology, we will describe the implementation of the web version of a specific visualization method, demonstrating how it can deal with both the requirements of scientific rigor in manipulating the data and the necessity to produce flexible and appealing rendering styles.