Volume 28 (2009)

Permanent URI for this community

https://diglib.eg.org/handle/10.2312/142

Browse

Now showing 1 - 20 of 241

Collaborative Brushing and Linking for Co-located Visual Analytics of Document Collections
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Isenberg, Petra; Fisher, Danyel; H.-C. Hege, I. Hotz, and T. Munzner
Many real-world analysis tasks can benefit from the combined efforts of a group of people. Past research has shown that to design visualizations for collaborative visual analytics tasks, we need to support both individual as well as joint analysis activities. We present Cambiera, a tabletop visual analytics tool that supports individual and collaborative information foraging activities in large text document collections. We define collaborative brushing and linking as an awareness mechanism that enables analysts to follow their own hypotheses during collaborative sessions while still remaining aware of the group's activities. With Cambiera, users are able to collaboratively search through documents, maintaining awareness of each others' work and building on each others' findings.
Illuminated 3D Scatterplots
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Sanftmann, Harald; Weiskopf, Daniel; H.-C. Hege, I. Hotz, and T. Munzner
In contrast to 2D scatterplots, the existing 3D variants have the advantage of showing one additional data dimension, but suffer from inadequate spatial and shape perception and therefore are not well suited to display structures of the underlying data. We improve shape perception by applying a new illumination technique to the pointcloud representation of 3D scatterplots. Points are classified as locally linear, planar, and volumetric structures according to the eigenvalues of the inverse distance-weighted covariance matrix at each data element. Based on this classification, different lighting models are applied: codimension-2 illumination, surface illumination, and emissive volumetric illumination. Our technique lends itself to efficient GPU point rendering and can be combined with existing methods like semi-transparent rendering, halos, and depth or attribute based color coding. The user can interactively navigate in the dataset and manipulate the classification and other visualization parameters. We demonstrate our visualization technique by showing examples of multi-dimensional data and of generic pointcloud data.
GPU Rendering of Relief Mapped Conical Frusta
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Bhagvat, D.; Jeschke, S.; Cline, D.; Wonka, P.
This paper proposes to use relief-mapped conical frusta (cones cut by planes) to skin skeletal objects. Based on this representation, current programmable graphics hardware can perform the rendering with only minimal communication between the CPU and GPU. A consistent definition of conical frusta including texture parametrization and a continuous surface normal is provided. Rendering is performed by analytical ray casting of the relief-mapped frusta directly on the GPU. We demonstrate both static and animated objects rendered using our technique and compare to polygonal renderings of similar quality.
Progressive Lossless Mesh Compression Via Incremental Parametric Refinement
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Valette, Sebastien; Chaine, Raphaelle; Prost, Remy
In this paper, we propose a novel progressive lossless mesh compression algorithm based on Incremental Parametric Refinement, where the connectivity is uncontrolled in a first step, yielding visually pleasing meshes at each resolution level while saving connectivity information compared to previous approaches. The algorithm starts with a coarse version of the original mesh, which is further refined by means of a novel refinement scheme. The mesh refinement is driven by a geometric criterion, in spirit with surface reconstruction algorithms, aiming at generating uniform meshes. The vertices coordinates are also quantized and transmitted in a progressive way, following a geometric criterion, efficiently allocating the bit budget. With this assumption, the generated intermediate meshes tend to exhibit a uniform sampling. The potential discrepancy between the resulting connectivity and the original one is corrected at the end of the algorithm. We provide a proof-of-concept implementation, yielding very competitive results compared to previous works in terms of rate/distortion trade-off.
Scalable real-time animation of rivers
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Yu, Qizhi; Neyret, Fabrice; Bruneton, Eric; Holzschuch, Nicolas
Many recent games and applications target the interactive exploration of realistic large scale worlds. These worlds consist mostly of static terrain models, as the simulation of animated fluids in these virtual worlds is computationally expensive. Adding flowing fluids, such as rivers, to these virtual worlds would greatly enhance their realism, but causes specific issues: as the user is usually observing the world at close range, small scale details such as waves and ripples are important. However, the large scale of the world makes classical methods impractical for simulating these effects. In this paper, we present an algorithm for the interactive simulation of realistic flowing fluids in large virtual worlds. Our method relies on two key contributions: the local computation of the velocity field of a steady flow given boundary conditions, and the advection of small scale details on a fluid, following the velocity field, and uniformly sampled in screen space.
Shadowing Dynamic Scenes with Arbitrary BRDFs
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Nowrouzezahrai, Derek; Kalogerakis, Evangelos; Fiume, Eugene
We present a real-time relighting and shadowing method for dynamic scenes with varying lighting, view and BRDFs. Our approach is based on a compact representation of reflectance data that allows for changing the BRDF at run-time and a data-driven method for accurately synthesizing self-shadows on articulated and deformable geometries. Unlike previous self-shadowing approaches, we do not rely on local blocking heuristics. We do not fit a model to the BRDF-weighted visibility, but rather only to the visibility that changes during animation. In this manner, our model is more compact than previous techniques and requires less computation both during fitting and at run-time. Our reflectance product operators can re-integrate arbitrary low-frequency view-dependent BRDF effects on-the-fly and are compatible with all previous dynamic visibility generation techniques as well as our own data-driven visibility model. We apply our reflectance product operators to three different visibility generation models, and our data-driven model can achieve framerates well over 300Hz.
An Analytical Solution to Single Scattering in Homogeneous Participating Media
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Pegoraro, Vincent; Parker, Steven G.
Despite their numerous applications, efficiently rendering participating media remains a challenging task due to the intricacy of the radiative transport equation. As they provide a generic means of solving a wide variety of problems, numerical methods are most often used to solve the air-light integral even under simplifying assumptions. In this paper, we present a novel analytical approach to single scattering from isotropic point light sources in homogeneous media. We derive the first closed-form solution to the air-light integral in isotropic media and extend this formulation to anisotropic phase functions. The technique relies neither on pre-computation nor on storage, and we provide a practical implementation allowing for an explicit control on the accuracy of the solutions. Finally, we demonstrate its quantitative and qualitative benefits over both previous numerical and analytical approaches.
MultiClusterTree: Interactive Visual Exploration of Hierarchical Clusters in Multidimensional Multivariate Data
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Long, Tran Van; Linsen, Lars; H.-C. Hege, I. Hotz, and T. Munzner
Visual analytics of multidimensional multivariate data is a challenging task because of the difficulty in understanding metrics in attribute spaces with more than three dimensions. Frequently, the analysis goal is not to look into individual records but to understand the distribution of the records at large and to find clusters of records with similar attribute values. A large number of (typically hierarchical) clustering algorithms have been developed to group individual records to clusters of statistical significance. However, only few visualization techniques exist for further exploring and understanding the clustering results. We propose visualization and interaction methods for analyzing individual clusters as well as cluster distribution within and across levels in the cluster hierarchy. We also provide a clustering method that operates on density rather than individual records. To not restrict our search for clusters, we compute density in the given multidimensional multivariate space. Clusters are formed by areas of high density. We present an approach that automatically computes a hierarchical tree of high density clusters. To visually represent the cluster hierarchy, we present a 2D radial layout that supports an intuitive understanding of the distribution structure of the multidimensional multivariate data set. Individual clusters can be explored interactively using parallel coordinates when being selected in the cluster tree. Furthermore, we integrate circular parallel coordinates into the radial hierarchical cluster tree layout, which allows for the analysis of the overall cluster distribution. This visual representation supports the comprehension of the relations between clusters and the original attributes. The combination of the 2D radial layout and the circular parallel coordinates is used to overcome the overplotting problem of parallel coordinates when looking into data sets with many records. We apply an automatic coloring scheme based on the 2D radial layout of the hierarchical cluster tree encoding hue, saturation, and value of the HSV color space. The colors support linking the 2D radial layout to other views such as the standard parallel coordinates or, in case data is obtained from multidimensional spatial data, the distribution in object space.
High Dynamic Range Imaging and Low Dynamic Range Expansion for Generating HDR Content
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Banterle, Francesco; Debattista, Kurt; Artusi, Alessandro; Pattanaik, Sumanta; Myszkowski, Karol; Ledda, Patrick; Chalmers, Alan
In the last few years, researchers in the field of High Dynamic Range (HDR) Imaging have focused on providing tools for expanding Low Dynamic Range (LDR) content for the generation of HDR images due to the growing popularity of HDR in applications, such as photography and rendering via Image-Based Lighting, and the imminent arrival of HDR displays to the consumer market. LDR content expansion is required due to the lack of fast and reliable consumer level HDR capture for still images and videos. Furthermore, LDR content expansion, will allow the re-use of legacy LDR stills, videos and LDR applications created, over the last century and more, to be widely available. The use of certain LDR expansion methods, those that are based on the inversion of Tone Mapping Operators (TMOs), has made it possible to create novel compression algorithms that tackle the problem of the size of HDR content storage, which remains one of the major obstacles to be overcome for the adoption of HDR. These methods are used in conjunction with traditional LDR compression methods and can evolve accordingly. The goal of this report is to provide a comprehensive overview on HDR Imaging, and an in depth review on these emerging topics.
BTF Compression via Sparse Tensor Decomposition
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ruiters, Roland; Klein, Reinhard
In this paper, we present a novel compression technique for Bidirectional Texture Functions based on a sparse tensor decomposition. We apply the K-SVD algorithm along two different modes of a tensor to decompose it into a small dictionary and two sparse tensors. This representation is very compact, allowing for considerably better compression ratios at the same RMS error than possible with current compression techniques like PCA, N-mode SVD and Per Cluster Factorization. In contrast to other tensor decomposition based techniques, the use of a sparse representation achieves a rendering performance that is at high compression ratios similar to PCA based methods.
A Robust Illumination Estimate for Chromatic Adaptation in Rendered Images
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Wilkie, Alexander; Weidlich, Andrea
We propose a method that improves automatic colour correction operations for rendered images. In particular, we propose a robust technique for estimating the visible and pertinent illumination in a given scene. We do this at very low computational cost by mostly re-using information that is already being computed during the image synthesis process. Conventional illuminant estimations either operate only on 2D image data, or, if they do go beyond pure image analysis, only use information on the luminaires found in the scene. The latter is usually done with little or no regard for how the light sources actually affect the part of the scene that is being viewed. Our technique goes beyond that, and also takes object reflectance into account, as well as the incident light that is actually responsible for the colour of the objects that one sees. It is therefore able to cope with difficult cases, such as scenes with mixed illuminants, complex scenes with many light sources of varying colour, or strongly coloured indirect illumination.
A Statistical Model of Human Pose and Body Shape
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Hasler, N.; Stoll, C.; Sunkel, M.; Rosenhahn, B.; Seidel, H.-P.
Generation and animation of realistic humans is an essential part of many projects in today s media industry. Especially, the games and special effects industry heavily depend on realistic human animation. In this work a unified model that describes both, human pose and body shape is introduced which allows us to accurately model muscle deformations not only as a function of pose but also dependent on the physique of the subject. Coupled with the model s ability to generate arbitrary human body shapes, it severely simplifies the generation of highly realistic character animations. A learning based approach is trained on approximately 550 full body 3D laser scans taken of 114 subjects. Scan registration is performed using a non-rigid deformation technique. Then, a rotation invariant encoding of the acquired exemplars permits the computation of a statistical model that simultaneously encodes pose and body shape. Finally, morphing or generating meshes according to several constraints simultaneously can be achieved by training semantically meaningful regressors.
TopoPlan: a topological path planner for real time human navigation under floor and ceiling constraints
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Lamarche, F.
In this article we present TopoPlan, a topological planner dedicated to real-time humanoid path-planning and motion adaptation to floor and ceiling constraints inside complex static environments. This planner analyzes unstructured 3D triangular meshes in order to automatically determine their topology. The analysis is based on a prismatic spatial subdivision which is analyzed, taking into account humanoid characteristics, in order to extract navigable surfaces and precisely identify environmental constraints such as floors, ceilings, walls, steps and bottlenecks. The technique also provides a lightweight roadmap computation covering all accessible free space. We demonstrate the properties of our topological planner within the context of two reactive motion control processes: an on-the-fly trajectory optimization and foot print generation process that correctly handles climbing of complex staircases, and a reactive ceiling adaptation process that handles beam avoidance and motion adaptation to irregular floors and ceilings. We further show that the computation cost of these processes is compatible with the real time animation of several dozens of virtual humans.
eNVyMyCar: A Multiplayer Car Racing Game for Teaching Computer Graphics
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ganovelli, F.; Corsini, M.
The development of a computer game is widely used as a way of conveying concepts regarding Computer Science. There are several reasons for this: it stimulates creativity, it provides an immediate sense of achievement (when the code works), it typically covers all the aspects of an introductory course, and it is easy to find ideas just by looking around and finding stimulation from one s environment and from fellow students. In this paper we present eNVyMyCar, a framework for the collaborative/competitive development of a computer game, and report the experience of its use in two Computer Graphics courses held in 2007. We developed a multiplayer car racing game where the student s task is just to implement the rendering of the scene, while all the other aspects, communication and synchronization are implemented in the framework and are transparent to the developer. The innovative feature of our framework is that all on-line users can see the views produced by their fellow students. This motivates students to improve their work by comparing it with other students and picking up ideas from them. It also gives students an opportunity to show off to their classmates.
A Psychophysical Evaluation of Inverse Tone Mapping Techniques
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Banterle, Francesco; Ledda, Patrick; Debattista, Kurt; Bloj, Marina; Artusi, Alessandro; Chalmers, Alan
In recent years inverse tone mapping techniques have been proposed for enhancing low-dynamic range (LDR) content for a high-dynamic range (HDR) experience on HDR displays, and for image based lighting. In this paper, we present a psychophysical study to evaluate the performance of inverse (reverse) tone mapping algorithms. Some of these techniques are computationally expensive because they need to resolve quantization problems that can occur when expanding an LDR image. Even if they can be implemented efficiently on hardware, the computational cost can still be high. An alternative is to utilize less complex operators; although these may suffer in terms of accuracy. Our study investigates, firstly, if a high level of complexity is needed for inverse tone mapping and, secondly, if a correlation exists between image content and quality. Two main applications have been considered: visualization on an HDR monitor and image-based lighting.
Interactive Geometric Simulation of 4D Cities
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Weber, Basil; Mueller, Pascal; Wonka, Peter; Gross, Markus
We present a simulation system that can simulate a three-dimensional urban model over time. The main novelty of our approach is that we do not rely on land-use simulation on a regular grid, but instead build a complete and inherently geometric simulation that includes exact parcel boundaries, streets of arbitrary orientation, street widths, 3D street geometry, building footprints, and 3D building envelopes. The second novelty is the fast simulation time and user interaction at interactive speed of about 1 second per time step.
COBRA: Compression of the Basis for PCA Represented Animations
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Vasa, L.; Skala, V.
Manifold Homotopy via the Flow Complex
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Sadri, Bardia
It is known that the critical points of the distance function induced by a dense sample P of a submanifold ? of R?n are distributed into two groups, one lying close to ? itself, called the shallow, and the other close to medial axis of ?, called deep critical points. We prove that under (uniform) sampling assumption, the union of stable manifolds of the shallow critical points have the same homotopy type as ? itself and the union of the stable manifolds of the deep critical points have the homotopy type of the complement of ?. The separation of critical points under uniform sampling entails a separation in terms of distance of critical points to the sample. This means that if a given sample is dense enough with respect to two or more submanifolds of R?n, the homotopy types of all such submanifolds together with those of their complements are captured as unions of stable manifolds of shallow versus those of deep critical points, in a filtration of the flow complex based on the distance of critical points to the sample. This results in an algorithm for homotopic manifold reconstruction when the target dimension is unknown.
Gromov-Hausdorff Stable Signatures for Shapes using Persistence
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Chazal, Frederic; Cohen-Steiner, David; Guibas, Leonidas J.; Memoli, Facundo; Oudot, Steve Y.
We introduce a family of signatures for finite metric spaces, possibly endowed with real valued functions, based on the persistence diagrams of suitable filtrations built on top of these spaces. We prove the stability of our signatures under Gromov-Hausdorff perturbations of the spaces. We also extend these results to metric spaces equipped with measures. Our signatures are well-suited for the study of unstructured point cloud data, which we illustrate through an application in shape classification.
Geometry Images of Arbitrary Genus in the Spherical Domain
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Gauthier, M.; Poulin, P.
While existing spherical parameterization algorithms are limited to genus-0 geometrical models, we believe a wide class of models of arbitrary genus can also benefit from the spherical domain. We present a complete and robust pipeline that can generate spherical geometry images from arbitrary genus surfaces where the holes are explicitly represented. The geometrical model, represented as a triangle mesh, is first made topologically equivalent to a sphere by cutting each hole along its generators, thus performing genus reduction. The resulting genus-0 model is then parameterized on the sphere, where it is resampled in a way to preserve connectivity between holes and to reduce the visual impact of seams due to these holes. Knowing the location of each pair of boundary components in parametric space, our novel sampling scheme can automatically choose to scale down or completely eliminate the associated hole, depending on geometry image resolution, thus lowering the genus of the reconstructed model. We found our method to scale better than other geometry image algorithms for higher genus models. We illustrate our approach on remeshing, level-of-detail rendering, normal mapping and topology editing.

Browse

Browsing Volume 28 (2009) by Issue Date

Results Per Page

Sort Options