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Item Tutorial 2 - Level-of-Detail in Surface and Volume Modeling(Eurographics Association, 1999) De Floriani, Leila; Puppo, Enrico; Cignoni, Paolo; Scopigno, Roberto-Item Normal Enhancement for Interactive Non-photorealistic Rendering(Eurographics Association, 2002) Cignoni, Paolo; Scopigno, Roberto; Tarini, MarcoWe present a simple technique to improve the perception of shape of an object. Bump mapping is well-known in the computer graphics community for providing the impression of small-scale geometrical features (which actually are not there). Here, we propose a similar approach (variation of normals) for the purpose of enhancing perception of the given geometry. Our approach is based on a simple modification of the surface normals in order to enhance the geometric features of the object during the rendering. The enhanced normals produced by this approach can be used in any rendering technique. The technique presented is particularly well suited to improve the rendering of mechanical parts where common cheap shading techniques can often generate shading ambiguities.Item Stereo Light Probe(The Eurographics Association and Blackwell Publishing Ltd, 2008) Corsini, Massimiliano; Callieri, Marco; Cignoni, PaoloIn this paper we present a practical, simple and robust method to acquire the spatially-varying illumination of a real-world scene. The basic idea of the proposed method is to acquire the radiance distribution of the scene using high-dynamic range images of two reflective balls. The use of two light probes instead of a single one allows to estimate, not only the direction and intensity of the light sources, but also the actual position in space of the light sources. To robustly achieve this goal we first rectify the two input spherical images, then, using a region-based stereo matching algorithm, we establish correspondences and compute the position of each light. The radiance distribution so obtained can be used for augmented reality applications, photo-realistic rendering and accurate reflectance properties estimation. The accuracy and the effectiveness of the method have been tested by measuring the computed light position and rendering synthetic version of a real object in the same scene. The comparison with standard method that uses a simple spherical lighting environment is also shown.Item Practical quad mesh simplification(The Eurographics Association and Blackwell Publishing Ltd, 2010) Tarini, Marco; Pietroni, Nico; Cignoni, Paolo; Panozzo, Daniele; Puppo, EnricoIn this paper we present an innovative approach to incremental quad mesh simplification, i.e. the task of producing a low complexity quad mesh starting from a high complexity one. The process is based on a novel set of strictly local operations which preserve quad structure. We show how good tessellation quality (e.g. in terms of vertex valencies) can be achieved by pursuing uniform length and canonical proportions of edges and diagonals. The decimation process is interleaved with smoothing in tangent space. The latter strongly contributes to identify a suitable sequence of local modification operations. The method is naturally extended to manage preservation of feature lines (e.g. creases) and varying (e.g. adaptive) tessellation densities. We also present an original Triangle-to-Quad conversion algorithm that behaves well in terms of geometrical complexity and tessellation quality, which we use to obtain the initial quad mesh from a given triangle mesh.Item Joint Interactive Visualization of 3D Models and Pictures in Walkable Scenes(The Eurographics Association, 2012) Brivio, Paolo; Tarini, Marco; Cignoni, Paolo; Scopigno, Roberto; Andrea Fusiello and Michael WimmerThe 3D digitalization of buildings, urban scenes, and the like is now a mature technology. Highly complex, densely sampled, reasonably accurate 3D models can be obtained by range-scanners and even image-based reconstruction methods from dense image collections. Acquisition of naked geometry is not enough in Cultural Heritage applications, because the surface colors (e.g. pictorial data) are clearly of central importance. Moreover, the 3D geometry cannot be expected to be complete, lacking context, parts made of materials like glass and metal, difficult to reach surfaces, etc. Easily captured photographs are the natural source of the appearance data missing in the 3D geometry. In spite of the recent availability of reliable technologies to align 2D images on 3D data, the two sides of the dataset are not easy to combine satisfactorily in a visualization. Texture mapping techniques, perhaps the most obvious candidate for the task, assume strict content consistency (3D to 2D, and 2D to 2D) which these datasets do not and should not exhibit (the advantage of pictures consisting in their ability to feature details, lighting conditions, non-persistent items, etc. which are absent in the 3D models or in the other pictures). In this work, we present a simple but effective technique to jointly and interactively visualize 2D and 3D data of this kind. This technique is used within PhotoCloud [IV12], a flexible opensource tool which is being designed to browse, navigate, and visualize large, remotely stored 3D-2D datasets, and which emphasizes scalability, usability, and ability to cope with heterogeneous data from various sources.Item EUROGRAPHICS 2019: Short Papers Frontmatter(Eurographics Association, 2019) Cignoni, Paolo; Miguel, Eder; Cignoni, Paolo and Miguel, EderItem Statics Aware Grid Shells(The Eurographics Association and John Wiley & Sons Ltd., 2015) Pietroni, Nico; Tonelli, Davide; Puppo, Enrico; Froli, Maurizio; Scopigno, Roberto; Cignoni, Paolo; Olga Sorkine-Hornung and Michael WimmerWe introduce a framework for the generation of polygonal grid-shell architectural structures, whose topology is designed in order to excel in static performances. We start from the analysis of stress on the input surface and we use the resulting tensor field to induce an anisotropic non-Euclidean metric over it. This metric is derived by studying the relation between the stress tensor over a continuous shell and the optimal shape of polygons in a corresponding grid-shell. Polygonal meshes with uniform density and isotropic cells under this metric exhibit variable density and anisotropy in Euclidean space, thus achieving a better distribution of the strain energy over their elements. Meshes are further optimized taking into account symmetry and regularity of cells to improve aesthetics. We experiment with quad meshes and hex-dominant meshes, demonstrating that our grid-shells achieve better static performances than state-of-the-art grid-shells.Item Optimizing Free-Form Grid Shells with Reclaimed Elements under Inventory Constraints(The Eurographics Association and John Wiley & Sons Ltd., 2025) Favilli, Andrea; Laccone, Francesco; Cignoni, Paolo; Malomo, Luigi; Giorgi, Daniela; Bousseau, Adrien; Day, AngelaWe propose a method for designing 3D architectural free-form surfaces, represented as grid shells with beams sourced from inventories of reclaimed elements from dismantled buildings. In inventory-constrained design, the reused elements must be paired with elements in the target design. Traditional solutions to this assignment problem often result in cuts and material waste or geometric distortions that affect the surface aesthetics and buildability. Our method for inventory-constrained assisted design blends the traditional assignment problem with differentiable geometry optimization to reduce cut-off waste while preserving the design intent. Additionally, we extend our approach to incorporate strain energy minimization for structural efficiency. We design differentiable losses that account for inventory, geometry, and structural constraints, and streamline them into a complete pipeline, demonstrated through several case studies. Our approach enables the reuse of existing elements for new designs, reducing the need for sourcing new materials and disposing of waste. Consequently, it can serve as an initial step towards mitigating the significant environmental impact of the construction sector.Item Automatic Image-Based Coral Polyp Analysis through Multi-View Instance Segmentation(The Eurographics Association, 2025) Dutta, Somnath; Pavoni, Gaia; Corsini, Massimiliano; Ganovelli, Fabio; Cignoni, Paolo; Rossi, Paolo; Cenni, Elena; Simonini, Roberto; Grassi, Francesca; Cassanelli, Davide; Cattini, Stefano; Rovati, Luigi; Capra, Alessandro; Castagnetti, Cristina; Günther, Tobias; Montazeri, ZahraWe present an automated framework for counting and measuring the polyps of Cladocora caespitosa, a Mediterranean reefbuilding coral. To our knowledge, the most practical method for counting polyps currently involves ecologists' visual inspection of a 3D model. However, measuring polyps from the model can lead to inaccuracies due to distortions in the reconstruction. Our method integrates deep learning-based instance segmentation on 2D images with 3D models for unique polyp identification, ensuring precise biometric extraction. The proposed pipeline automates polyp detection, counting, and measurement while overcoming the limitations of manual in situ methods. Laboratory validation demonstrates its accuracy and efficiency, paving the way for scalable, high-resolution phenotyping, and field monitoring of Mediterranean coral populations.Item NOVA-3DGS: No-reference Objective VAlidation for 3D Gaussian Splatting(The Eurographics Association, 2025) Piras, Valentina; Bonatti, Amedeo Franco; Maria, Carmelo De; Cignoni, Paolo; Banterle, Francesco; Günther, Tobias; Montazeri, ZahraIn recent years, radiance field methods, and in particular 3D Gaussian Splatting (3DGS), have distinguished themselves in the field of image-based rendering and scene reconstruction techniques, gaining significant success in academia and being cited in numerous research papers. Like other methods, 3DGS requires a large and diverse dataset of images for network training as a fundamental step to ensure effectiveness and high-quality results. Consequently, the acquisition phase is highly time-consuming, especially considering that a portion of the acquired dataset is not actually used for training but is reserved for testing. This is necessary because all commonly used metrics for evaluating the quality of 3D reconstructions, such as PSNR and SSIM, are reference-based metrics; i.e., requiring a ground truth. In this work, we present NOVA, a study focused on no-reference evaluation of 3DGS renders, based on key metrics in this field: PSNR and SSIM.