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Item Adaptive Clipping of Splats to Models with Sharp Features(The Eurographics Association, 2014) Ivo, Rafael; Ganovelli, Fabio; Vidal, Creto; Scopigno, Roberto; Andrea GiachettiSplat-based models are a good representation because of its absense of topology, making complex modeling operations easier, but keeping the same approximation ratio from triangular meshes. However corners cannot be properly represented by splats without clipping them. We present a new method for clipping splats in models with sharp features. Each splat is an ellipse equipped with a few parameters that allow to define how the ellipse can be clipped against a bidimensional rational Bézier curve and thus it can be used for all those surfaces that show a large number of edge features and different sampling rate around them. The simple and uniform data used to define the clipping curve makes easy the implementation in GPU. We designed and implemented an automatic computation of the clipping curves and a pipeline for sampling a generic surface with splats and render it. In this paper we show how this technique outperforms the previous clipping techniques in precision for objects such as mechanical parts and CAD- like models keeping the rendering speed.Item Two Examples of GPGPU Acceleration of Memory-intensive Algorithms(The Eurographics Association, 2010) Marras, Stefano; Mura, Claudio; Gobbetti, Enrico; Scateni, Riccardo; Scopigno, Roberto; Enrico Puppo and Andrea Brogni and Leila De FlorianiThe advent of GPGPU technologies has allowed for sensible speed-ups in many high-dimension, memory-intensive computational problems. In this paper we demonstrate the e ectiveness of such techniques by describing two applications of GPGPU computing to two di erent subfields of computer graphics, namely computer vision and mesh processing. In the first case, CUDA technology is employed to accelerate the computation of approximation of motion between two images, known also as optical flow. As for mesh processing, we exploit the massivelyparallel architecture of CUDA devices to accelerate the face clustering procedure that is employed in many recent mesh segmentation algorithms. In both cases, the results obtained so far are presented and thoroughly discussed, along with the expected future development of the work.Item Practical and Robust MLS-based Integration of Scanned Data(The Eurographics Association, 2008) Fiorin, Valentino; Cignoni, Paolo; Scopigno, Roberto; Vittorio Scarano and Rosario De Chiara and Ugo ErraThe paper proposes a set of techniques for improving the quality of MLS surfaces reconstructed from point clouds that are composed by the union of many scanned range maps. The main idea of those techniques is that the range-map structure should be exploited during the reconstruction process and not lost in the uniform point soup that is usually fed into reconstruction algorithms; on this purpose a set of per-range-map weighting schemes are proposed. The presented weighting schemes allow to cope with some of the various issues that usually arise during the integration of point clouds composed by set of range maps, like tangible alignment errors, anisotropic error on sensor data and sensible difference in sampling quality.Item Generalized Trackball for Surfing Over Surfaces(The Eurographics Association, 2016) Malomo, Luigi; Cignoni, Paolo; Scopigno, Roberto; Giovanni Pintore and Filippo StancoWe 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.Item Automating Large 3D Dataset Publication in a Web-Based Multimedia Repository(The Eurographics Association, 2016) Potenziani, Marco; Fritsch, Bernhard; Dellepiane, Matteo; Scopigno, Roberto; Giovanni Pintore and Filippo StancoOnline publishing of almost every type of 3D data has become a quasi-standard routine. Nevertheless, the integration in a web page of a single 3D model, or of a predefined restricted set of models, raises different issues compared to an efficient and effective integration of thousands of them in an online repository. In this case it is mandatory to have an automatized pipeline to prepare and homogenize the dataset. The pipeline should be able to automatically wrap 3D data in all conditions, and display every single model with the best scene setup without any (or with a minimal) interaction by the database maintainers. This paper, retracing the steps of a recent real application case, aims at showing all the faced issues (and the adopted solutions) to publish a large and heterogeneous three-dimensional dataset in a web specialized repository. We want to introduce a valid and reusable strategy, starting from the description of the pipeline adopted for data pre-processing and moving to the choices made in the 3D viewer implementation. The paper concludes with a discussion on the actual state of the integration of 3D data with the other multimedia informative layers.Item Multiple Uses of 3D Scanning for the Valorization of an Artistic Site: the Case of Luni(The Eurographics Association, 2008) Dellepiane, Matteo; Callieri, Marco; Paribeni, Emanuela; Sorge, Elena; Sulfaro, Nino; Marianelli, Veronica; Scopigno, Roberto; Vittorio Scarano and Rosario De Chiara and Ugo ErraThe heritage site of Luni is a very interesting location, which tells the story of an ancient roman colony, and of an area where different cultures left their heritage. In particular, the remains of the pediments of an ancient temple represent a very interesting case and an open field of study for art historians. The scanning of a group of statue belonging to the pediments showed that the produced 3D models could be used in several ways, not only for archival and presentation purposes but also to provide interactive support for the work of the restorers and the scholars. In particular, the use of 3D models to propose and validate hypothesis about the original position of the fragments in the context of the fronton could be an alternative solution to the direct manipulation of them. Moreover, the analysis of the original color of the statues, and the representation different hypothesis about the ancient appearance can be produced through the interactive editing of the 3D models of the statues. In this paper we present the scanning campaign which resulted in the acquisition of five statues,the preliminary results of some of the uses of the models produced with acquired data, and a brief description of other possible future applications of them. This shows how 3D scanning can be considered by now a mature technology for the support of restoration and preservation of Cultural Heritage.Item Mutual Correspondences: An Hybrid Method for Image-to-geometry Registration(The Eurographics Association, 2010) Sottile, Michele; Dellepiane, Matteo; Cignoni, Paolo; Scopigno, Roberto; Enrico Puppo and Andrea Brogni and Leila De FlorianiImage registration is an important task in several applications of Computer Graphics and Computer Vision. Among the large number of proposed approaches, currently there is no solution which is automatic and robust enough to handle any general case. The most robust methods usually require a significant intervention by the user to specify many 2D-3D correspondences, while automatic techniques often rely on strong assumptions about the quality of 2D and 3D data. In this paper we present Mutual Correspondences, which is based on a minimization function which combines correspondences based and Mutual Information based approaches, and takes advantage of the strong points of both. Mutual Correspondences give the user the possibility to "guide" Mutual Information with only a few 2D- 3D correspondences. The proposed approach results in a wider convergence range and in higher registration accuracy, regardless of the quality of both the image and the 3D model. Mutual Correspondences were applied on some practical cases, where state-of-the-art approaches tended to fail, and they provided a mean to obtain accurate results. This led to a simple, robust and practical approach that can provide a way to register images in a few seconds.Item Improving 2D-3D Registration by Mutual Information using Gradient Maps(The Eurographics Association, 2010) Palma, Gianpaolo; Corsini, Massimiliano; Dellepiane, Matteo; Scopigno, Roberto; Enrico Puppo and Andrea Brogni and Leila De FlorianiIn this paper we propose an extension for the algorithms of image-to-geometry registration by Mutual Information( MI) to improve the performance and the quality of the alignment. Proposed for the registration of multi modal medical images, in the last years MI has been adapted to align a 3D model to a given image by using different renderings of the model and a gray-scale version of the input image. A key aspect is the choice of the rendering process to correlate the 3D model to the image without taking into account the texture data and the lighting conditions. Even if several rendering types for the 3D model have been analyzed, in some cases the alignment fails for two main reasons: the peculiar reflection behavior of the object that we are not able to reproduce in the rendering of the 3D model without knowing the material characteristics of the object and the lighting conditions of the acquisition environment; the characteristics of the image background, especially non uniform background, that can degrade the convergence of the registration. To improve the quality of the registration in these cases we propose to compute the MI between the gradient map of the 3D rendering and the gradient map of the image in order to maximize the shared data between them.Item Stereo-browsing from Calibrated Cameras(The Eurographics Association, 2014) Baldacci, Andrea; Ganovelli, Fabio; Corsini, Massimiliano; Scopigno, Roberto; Andrea GiachettiModern Structure-from-Motion (SfM) methods enable the registration of a set of cameras and the reconstruction of the corresponding sparse point cloud of the object/location depicted in the input images. Despite the quality of such techniques they often fail where the input point cloud has a very low density thus decreasing the final user experience. On the other side, modern image-based rendering (IBR) techniques try to avoid a full reconstruction of the geometry by empowering the user with interfaces for the smooth navigation of the acquired images. In such methods, images viewed from viewpoints in-between the actual cameras are generated in some way, for example by using a textured proxy or by warping properly the input images. Usual navigation interfaces, however, neglect to use the inherent nature of such set of cameras which, despite having a wide-baseline, are often well spatially organized as they usually maintain a good overlap between images, varying smoothly both the position and the orientation of the camera. Given such a set of registered cameras, we present a framework for the stereoscopic exploration of the object/location depicted using any type of stereoscopic devices. In the proposed system, the users can have a full tridimensional experience without the need of a complete 3D reconstruction. Our method starts by building a graph where each node is associated to a calibrated camera that represents a virtual eye. Two virtual eyes give a stereo pair. Along each edge of this graph we can instantiate a novel virtual camera using simple linear interpolation of the extrinsic parameters and we can generate its corresponding novel view by using known IBR techniques. This, in practice, extends the domain of the possible views from the discrete set of acquired cameras to a continuous domain given by our graph. Combining any couple of cameras that we can pick on this graph we obtain the set of all possible stereo pairs, that is the codomain of our graph. We give a formal definition of this space, that we called StereoSpace. Built on this, we designed our prototype system for the stereoscopic exploration of photo collections.Item Design and Fabrication of Grid-shells Mockups(The Eurographics Association, 2016) Tonelli, Davide; Pietroni, Nico; Cignoni, Paolo; Scopigno, Roberto; Giovanni Pintore and Filippo StancoStatics Aware Voronoi Grid-shells have been recently introduced in the Architectural Geometry field. These are innovative gridshells endowed with a polygonal topology, whose geometry is structurally optimized by means of a novel algorithm [PTP+15]. Although being structurally effective as proved in [TPP+16] and arguably aesthetically charming, so far these grid-shells have struggled to attract architects' interest. We propose a method to fabricate a mockup of the grid shell by using modern additive 3D printing and laser cutting technologies. We also show how the realised mockup can be used to perform a preliminary validation of the simulated static performances of the grid-shell structure.