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Interlocking Pieces for Printing Tangible Cultural Heritage Replicas
(The Eurographics Association, 2014) Alemanno, Giuseppe; Cignoni, Paolo; Pietroni, Nico; Ponchio, Federico; Scopigno, Roberto; Reinhard Klein and Pedro Santos
We propose a technique to decompose a 3D digital shape into a set of interlocking pieces that are easy to be manufactured and assembled. The pieces are designed so that they can be represented as a simple height field and, therefore, they can be manufactured by common 3D printers without the usage of supporting material. The removal of the supporting material is often a burdensome task and may eventually damage the surface of the printed object. Our approach makes the final reproduction cheaper, accurate and suitable for the reproduction of tangible cultural heritages. Moreover, since the proposed technique decomposes the artwork in pieces, it also overcomes the working space limits of common printers. The decomposition of the input (high-resolution) triangular mesh is driven by a coarse polygonal base mesh (representing the target subdivision in pieces); the height fields defining each piece are generated by sampling distances along the normal of each face composing the base mesh. A innovative interlocking mechanism allows adjacent pieces to plug each other to compose the final shape. This interlocking mechanism is designed to preserve the height field property of the pieces and to provide a sufficient degree of grip to ensure the assembled structure shape to be compact and stable. We demonstrate the effectiveness of our approach and show its limitations with some practical reproduction examples.
High Dynamic Range Point Clouds for Real-Time Relighting
(The Eurographics Association and John Wiley & Sons Ltd., 2019) Sabbadin, Manuele; Palma, Gianpaolo; BANTERLE, FRANCESCO; Boubekeur, Tamy; Cignoni, Paolo; Lee, Jehee and Theobalt, Christian and Wetzstein, Gordon
Acquired 3D point clouds make possible quick modeling of virtual scenes from the real world.With modern 3D capture pipelines, each point sample often comes with additional attributes such as normal vector and color response. Although rendering and processing such data has been extensively studied, little attention has been devoted using the light transport hidden in the recorded per-sample color response to relight virtual objects in visual effects (VFX) look-dev or augmented reality (AR) scenarios. Typically, standard relighting environment exploits global environment maps together with a collection of local light probes to reflect the light mood of the real scene on the virtual object. We propose instead a unified spatial approximation of the radiance and visibility relationships present in the scene, in the form of a colored point cloud. To do so, our method relies on two core components: High Dynamic Range (HDR) expansion and real-time Point-Based Global Illumination (PBGI). First, since an acquired color point cloud typically comes in Low Dynamic Range (LDR) format, we boost it using a single HDR photo exemplar of the captured scene that can cover part of it. We perform this expansion efficiently by first expanding the dynamic range of a set of renderings of the point cloud and then projecting these renderings on the original cloud. At this stage, we propagate the expansion to the regions not covered by the renderings or with low-quality dynamic range by solving a Poisson system. Then, at rendering time, we use the resulting HDR point cloud to relight virtual objects, providing a diffuse model of the indirect illumination propagated by the environment. To do so, we design a PBGI algorithm that exploits the GPU's geometry shader stage as well as a new mipmapping operator, tailored for G-buffers, to achieve real-time performances. As a result, our method can effectively relight virtual objects exhibiting diffuse and glossy physically-based materials in real time. Furthermore, it accounts for the spatial embedding of the object within the 3D environment. We evaluate our approach on manufactured scenes to assess the error introduced at every step from the perfect ground truth. We also report experiments with real captured data, covering a range of capture technologies, from active scanning to multiview stereo reconstruction.
PileBars: Scalable Dynamic Thumbnail Bars
(The Eurographics Association, 2012) Brivio, Paolo; Tarini, Marco; Ponchio, Federico; Cignoni, Paolo; Scopigno, Roberto; David Arnold and Jaime Kaminski and Franco Niccolucci and Andre Stork
We introduce PileBars, a new class of animated thumbnail-bars supporting browsing of large image datasets (hundreds or thousands of images). Since the bar is meant to be just one element of a GUI, it covers only a small portion of the screen; yet it provides a global view of the entire dataset, without any scrolling panel. Instead, thumbnails are dynamically rearranged, resized and reclustered into adaptive layouts during the entire browsing process. The objective is to enable the user both to accurately pinpoint a specific image (even among semantically close ones), and to jump anywhere to ''distant'' parts of the dataset. The thumbnail layouts proposed maximize also the temporal coherence, thus allowing for smooth animations from one layout to the next. The system is very general: it can be driven by any application-specific image-to-image semantic distance function, and respects any user-defined total ordering of the images; the ordering can be either inferred from the semantic or be chosen independently from it, depending on the application. The applicability of the resulting system is tested in a number of practical applications and fits very well the issues in management of Cultural Heritage image collections.
Surface Light Field from Video Acquired in Uncontrolled Settings
(The Eurographics Association, 2013) Palma, Gianpaolo; Desogus, Nicola; Cignoni, Paolo; Scopigno, Roberto; -
This paper presents an algorithm for the estimation of the Surface Light Field using video sequences acquired moving the camera around the object. Unlike other state of the art methods, it does not require a uniform sampling density of the view directions, but it is able to build an approximation of the Surface Light Field starting from a biased video acquisition: dense along the camera path and completely missing in the other directions. The main idea is to separate the estimation of two components: the diffuse color, computed using statistical operations that allow the estimation of a rough approximation of the direction of the main light sources in the acquisition environment; the other residual Surface Light Field effects, modeled as linear combination of spherical functions. From qualitative and numerical evaluations, the final rendering results show a high fidelity and similarity with the input video frames, without ringing and banding effects.
Generalized Trackball for Surfing Over Surfaces
(The Eurographics Association, 2016) Malomo, Luigi; Cignoni, Paolo; Scopigno, Roberto; Giovanni Pintore and Filippo Stanco
We present an efficient 3D interaction technique: generalizing the well known trackball approach, this technique unifies and blends the two common interaction mechanisms known as panning and orbiting. The approach allows to inspect a virtual object by navigating over its surrounding space, remaining at a chosen distance and performing an automatic panning over its surface. This generalized trackball allows an intuitive navigation of topologically complex shapes, enabling unexperienced users to visit hard-to-reach parts better and faster than with standard GUI components. The approach is based on the construction of multiple smooth approximations of the model under inspection; at rendering time, it constrains the camera to stay at a given distance to these approximations. The approach requires negligible preprocessing and memory overhead and works well for both mousebased and touch interfaces. An informal user study confirms the impact of the proposed technique.
Detection of Geometric Temporal Changes in Point Clouds
(Copyright © 2016 The Eurographics Association and John Wiley & Sons Ltd., 2016) Palma, Gianpaolo; Cignoni, Paolo; Boubekeur, Tamy; Scopigno, Roberto; Chen, Min and Zhang, Hao (Richard)
Detecting geometric changes between two 3D captures of the same location performed at different moments is a critical operation for all systems requiring a precise segmentation between change and no‐change regions. Such application scenarios include 3D surface reconstruction, environment monitoring, natural events management and forensic science. Unfortunately, typical 3D scanning setups cannot provide any one‐to‐one mapping between measured samples in static regions: in particular, both extrinsic and intrinsic sensor parameters may vary over time while sensor noise and outliers additionally corrupt the data. In this paper, we adopt a multi‐scale approach to robustly tackle these issues. Starting from two point clouds, we first remove outliers using a probabilistic operator. Then, we detect the actual change using the implicit surface defined by the point clouds under a Growing Least Square reconstruction that, compared to the classical proximity measure, offers a more robust change/no‐change characterization near the temporal intersection of the scans and in the areas exhibiting different sampling density and direction. The resulting classification is enhanced with a spatial reasoning step to solve critical geometric configurations that are common in man‐made environments. We validate our approach on a synthetic test case and on a collection of real data sets acquired using commodity hardware. Finally, we show how 3D reconstruction benefits from the resulting precise change/no‐change segmentation.Detecting geometric changes between two 3D captures of the same location performed at different moments is a critical operation for all systems requiring a precise segmentation between change and no‐change regions. Unfortunately, typical 3D scanning setups cannot provide any oneto‐one mapping between measured samples in static regions: both extrinsic and intrinsic sensor parameters may vary over time while sensor noise and outliers additionally corrupt the data. In this paper, we adopt a multi‐scale approach to robustly tackle these issues, obtaining a robust segmentation near the temporal intersection of the scans and in the areas with different sampling density and direction.
A computer-assisted constraint-based system for assembling fragmented objects
(The Eurographics Association, 2013) Palmas, Gregorio; Pietroni, Nico; Cignoni, Paolo; Scopigno, Roberto; -
We propose a computer-assisted constraint-based methodology for virtual reassembly of Cultural Heritage (CH) artworks. Instead than focusing on automatic, unassisted reassembly, we targeted the scenarios where the reconstruction process is not be based on shape properties only but it is build over the experience and intuition of a CH expert. Our purpose is therefore to design a flexible interactive system, based on the selection of a set of constraints which relates different fragments, according to the understanding and experience of the CH operator. Once the user has defined those constraints, the system searches for a suitable solution, using a global energy minimization strategy that considers simultaneously all the pieces involved in the reconstruction process. Additionally, our framework provides the possibility to work in a hierarchical way, mimicking the traditional physical procedure that archaeologists use to reassemble tangible fractured objects. The frameworks is designed to work even with fragments that could have been severely damaged or eroded. On those datasets, automatic approaches may often fail, since the fractured regions do not contain enough geometric information to infer the correct matches. We present some successful uses of our framework on real application scenarios.
Harvesting Dynamic 3D Worlds from Commodity Sensor Clouds
(The Eurographics Association, 2016) Boubekeur, Tamy; Cignoni, Paolo; Eisemann, Elmar; Goesele, Michael; Klein, Reinhard; Roth, Stefan; Weinmann, Michael; Wimmer, Michael; Chiara Eva Catalano and Livio De Luca
The EU FP7 FET-Open project ''Harvest4D: Harvesting Dynamic 3D Worlds from Commodity Sensor Clouds'' deals with the acquisition, processing, and display of dynamic 3D data. Technological progress is offering us a wide-spread availability of sensing devices that deliver different data streams, which can be easily deployed in the real world and produce streams of sampled data with increased density and easier iteration of the sampling process. These data need to be processed and displayed in a new way. The Harvest4D project proposes a radical change in acquisition and processing technology: instead of a goaldriven acquisition that determines the devices and sensors, its methods let the sensors and resulting available data determine the acquisition process. A variety of challenging problems need to be solved: huge data amounts, different modalities, varying scales, dynamic, noisy and colorful data. This short contribution presents a selection of the many scientific results produced by Harvest4D. We will focus on those results that could bring a major impact to the Cultural Heritage domain, namely facilitating the acquisition of the sampled data or providing advanced visual analysis capabilities.
Anisotropic MatCap: Easy Capture and Reproduction of Anisotropic Materials
(The Eurographics Association, 2016) Magri, Dario; Cignoni, Paolo; Tarini, Marco; Giovanni Pintore and Filippo Stanco
We propose Anisotropic MatCap, a simple data structure based on a small volumetric texture that is able to represent, under a fixed lighting, the behavior of anisotropic materials. The data structure is designed to allow fast and practical capture of real-world anisotropic materials (like for example fabrics) and to be used in real-time renderings, requiring only negligible time and texture memory overheads. The resulting technique is suited for application scenarios where digital objects must be inspected by an end user, recreating the look of an object made of a captured anisotropic material and seen under the predetermined lighting conditions. The technique proved particularly useful for garments and cloth visualization and design.
State of The Art on Functional Fabrication
(The Eurographics Association, 2016) Sá, Asla Medeiros e; Echavarria, Karina Rodriguez; Pietroni, Nico; Cignoni, Paolo; A. Medeiros e Sa and N. Pietroni and K. Rodriguez Echavarria
Digital fabrication technologies are becoming of importance to a number of knowledge areas and sectors, including medicine, entertainment, design, engineering, education, arts and architecture, due to their accessibility and versatility. These technologies are changing the design of digital models, materials and manufacturing processes which enable to build previously unachievable physical objects. Since many constraints imposed on the design of objects have changed significantly, a growing research community is working on graphical tools and techniques to enable the conception, automation, production and usage of innovative and complex designs for fabrication. In the present work, we survey the state of the art of computer graphics contributions to functional fabrication design tools and techniques. By functional fabrication we understand the design and manufacture of physical objects which functionalities exploit the capabilities of digital fabrication technologies. These functionalities include improving the mechanics of a workpiece, producing articulated models, capturing aerodynamics, planning deformable workpieces and controlling the object’'s appearance and acoustics. The resulting design tools are clearly taking advantage of relevant computer graphics techniques. Furthermore, they are extending these techniques to realise new physical forms as well as bringing innovation to feed into the design space.

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