Volume 27 (2008)

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Preface, Table of Contents, Cover
(The Eurographics Association and Blackwell Publishing, Inc, 2008)
Efficient CPU-based Volume Ray Tracing Techniques
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Marmitt, Gerd; Friedrich, Heiko; Slusallek, Philipp
Recent research on high-performance ray tracing has achieved real-time performance even for highly complex surface models already on a single PC. In this report, we provide an overview of techniques for extending real-time ray tracing also to interactive volume rendering. We review fast rendering techniques for different volume representations and rendering modes in a variety of computing environments. The physically-based rendering approach of ray tracing enables high image quality and allows for easily mixing surface, volume and other primitives in a scene, while fully accounting for all of their optical interactions. We present optimized implementations and discuss the use of upcoming high-performance processors for volume ray tracing.
Streaming Surface Reconstruction Using Wavelets
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Manson, J.; Petrova, G.; Schaefer, S.
We present a streaming method for reconstructing surfaces from large data sets generated by a laser range scanner using wavelets. Wavelets provide a localized, multiresolution representation of functions and this makes them ideal candidates for streaming surface reconstruction algorithms. We show how wavelets can be used to reconstruct the indicator function of a shape from a cloud of points with associated normals. Our method proceeds in several steps. We first compute a low-resolution approximation of the indicator function using an octree followed by a second pass that incrementally adds fine resolution details. The indicator function is then smoothed using a modified octree convolution step and contoured to produce the final surface. Due to the local, multiresolution nature of wavelets, our approach results in an algorithm over 10 times faster than previous methods and can process extremely large data sets in the order of several hundred million points in only an hour.
Particle Level Set Advection for the Interactive Visualization of Unsteady 3D Flow
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Cuntz, Nicolas; Kolb, Andreas; Strzodka, Robert; Weiskopf, Daniel; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
Typically, flow volumes are visualized by defining their boundary as iso-surface of a level set function. Grid-based level sets offer a good global representation but suffer from numerical diffusion of surface detail, whereas particlebased methods preserve details more accurately but introduce the problem of unequal global representation. The particle level set (PLS) method combines the advantages of both approaches by interchanging the information between the grid and the particles. Our work demonstrates that the PLS technique can be adapted to volumetric dye advection via streak volumes, and to the visualization by time surfaces and path volumes. We achieve this with a modified and extended PLS, including a model for dye injection. A new algorithmic interpretation of PLS is introduced to exploit the efficiency of the GPU, leading to interactive visualization. Finally, we demonstrate the high quality and usefulness of PLS flow visualization by providing quantitative results on volume preservation and by discussing typical applications of 3D flow visualization.
A Prism-Free Method for Silhouette Rendering in Inverse Displacement Mapping
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Chen, Ying-Chieh; Chang, Chun-Fa
Silhouette is a key feature that distinguishes displacement mapping from normal mapping. However the silhouette rendering in the GPU implementation of displacement mapping (which is often called inversed displacement mapping) is tricky. Previous approaches rely mostly on construction of additional extruding prism-like geometry, which slows down the rendering significantly. In this paper, we proposed a method for solving the silhouette rendering problem in inverse displace mapping without using any extruding prism-like geometry. At each step of intersection finding, we continuously bends the viewing ray according to the current local tangent space associated with the surface. Thus, it allows mapping a displacement map onto an arbitrary curved surface with more accurate silhouette. While our method is simple, it offers surprisingly good results over Curved Relief Map (CRM) [OP05] in many difficult or degenerated cases.
Surface Reconstruction From Non-parallel Curve Networks
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Liu, L.; Bajaj, C.; Deasy, J. O.; Low, D. A.; Ju, T.
Building surfaces from cross-section curves has wide applications including bio-medical modeling. Previous work in this area has mostly focused on connecting simple closed curves on parallel cross-sections. Here we consider the more general problem where input data may lie on non-parallel cross-sections and consist of curve networks that represent the segmentation of the underlying object by different material or tissue types (e.g., skin, muscle, bone, etc.) on each cross-section. The desired output is a surface network that models both the exterior surface and the internal partitioning of the object. We introduce an algorithm that is capable of handling curve networks of arbitrary shape and topology on cross-section planes with arbitrary orientations. Our algorithm is simple to implement and is guaranteed to produce a closed surface network that interpolates the curve network on each cross-section. Our method is demonstrated on both synthetic and bio-medical examples.
Sketching and Composing Widgets for 3D Manipulation
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Schmidt, Ryan; Singh, Karan; Balakrishnan, Ravin
We present an interface for 3D object manipulation in which standard transformation tools are replaced with transient 3D widgets invoked by sketching context-dependent strokes. The widgets are automatically aligned to axes and planes determined by the user s stroke. Sketched pivot-points further expand the interaction vocabulary. Using gestural commands, these basic elements can be assembled into dynamic, user-constructed 3D transformation systems. We supplement precise widget interaction with techniques for coarse object positioning and snapping. Our approach, which is implemented within a broader sketch-based modeling system, also integrates an underlying widget history to enable the fluid transfer of widgets between objects. An evaluation indicates that users familiar with 3D manipulation concepts can be taught how to efficiently use our system in under an hour.
Curvature-Domain Shape Processing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Eigensatz, Michael; Sumner, Robert W.; Pauly, Mark
We propose a framework for 3D geometry processing that provides direct access to surface curvature to facilitate advanced shape editing, filtering, and synthesis algorithms. The central idea is to map a given surface to the curvature domain by evaluating its principle curvatures, apply filtering and editing operations to the curvature distribution, and reconstruct the resulting surface using an optimization approach. Our system allows the user to prescribe arbitrary principle curvature values anywhere on the surface. The optimization solves a nonlinear least-squares problem to find the surface that best matches the desired target curvatures while preserving important properties of the original shape. We demonstrate the effectiveness of this processing metaphor with several applications, including anisotropic smoothing, feature enhancement, and multi-scale curvature editing.
Volume and Isosurface Rendering with GPU-Accelerated Cell Projection*
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Marroquim, R.; Maximo, A.; Farias, R.; Esperanca, C.
We present an efficient Graphics Processing Unit GPU-based implementation of the Projected Tetrahedra (PT) algorithm. By reducing most of the CPU-GPU data transfer, the algorithm achieves interactive frame rates (up to 2.0 M Tets/s) on current graphics hardware. Since no topology information is stored, it requires substantially less memory than recent interactive ray casting approaches. The method uses a two-pass GPU approach with two fragment shaders. This work includes extended volume inspection capabilities by supporting interactive transfer function editing and isosurface highlighting using a Phong illumination model.
Geometry Textures and Applications
(The Eurographics Association and Blackwell Publishing Ltd, 2008) De Toledo, Rodrigo; Wang, Bin; Levy, Bruno
Geometry textures are a novel geometric representation for surfaces based on height maps. The visualization is done through a graphics processing unit (GPU) ray casting algorithm applied to the whole object. At rendering time, the fine-scale details (mesostructures) are reconstructed preserving original quality. Visualizing surfaces with geometry textures allows a natural level-of-detail (LOD) behaviour. There are numerous applications that can benefit from the use of geometry textures. In this paper, besides a mesostructure visualization survey, we present geometry textures with three possible applications: rendering of solid models, geological surfaces visualization and surface smoothing.
Free Form Incident Light Fields
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Unger, J.; Gustavson, S.; Larsson, P.; Ynnerman, A.
This paper presents methods for photo-realistic rendering using strongly spatially variant illumination captured from real scenes. The illumination is captured along arbitrary paths in space using a high dynamic range, HDR, video camera system with position tracking. Light samples are rearranged into 4-D incident light fields (ILF) suitable for direct use as illumination in renderings. Analysis of the captured data allows for estimation of the shape, position and spatial and angular properties of light sources in the scene. The estimated light sources can be extracted from the large 4D data set and handled separately to render scenes more efficiently and with higher quality. The ILF lighting can also be edited for detailed artistic control.
Detail-In-Context Visualization for Satellite Imagery
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Boettger, Joachim; Preiser, Martin; Balzer, Michael; Deussen, Oliver
We use the complex logarithm as a transformation for the visualization and navigation of highly complex satellite and aerial imagery. The resulting depictions show details and context with greatly different scales in one seamless image while avoiding local distortions. We motivate our approach by showing its relations to the ordinary perspective views and classical map projections. We discuss how to organize and process the huge amount of imagery in realtime using modern graphics hardware with an extended clipmapping technique. Finally, we provide details and experiences concerning the interpretation of and interaction with the resulting representations.
Irradiance Gradients in the Presence of Participating Media and Occlusions
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Jarosz, Wojciech; Zwicker, Matthias; Jensen, Henrik Wann
In this paper we present a technique for computing translational gradients of indirect surface reflectance in scenes containing participating media and significant occlusions. These gradients describe how the incident radiance field changes with respect to translation on surfaces. Previous techniques for computing gradients ignore the effects of volume scattering and attenuation and assume that radiance is constant along rays connecting surfaces. We present a novel gradient formulation that correctly captures the influence of participating media. Our formulation accurately accounts for changes of occlusion, including the effect of surfaces occluding scattering media. We show how the proposed gradients can be used within an irradiance caching framework to more accurately handle scenes with participating media, providing significant improvements in interpolation quality.
A Hierarchical Segmentation of Articulated Bodies
(The Eurographics Association and Blackwell Publishing Ltd, 2008) De Goes, Fernando; Goldenstein, Siome; Velho, Luiz
This paper presents a novel segmentation method to assist the rigging of articulated bodies. The method computes a coarse-to-fine hierarchy of segments ordered by the level of detail. The results are invariant to deformations, and numerically robust to noise, irregular tessellations, and topological short-circuits. The segmentation is based on two key ideas. First, it exploits the multiscale properties of the diffusion distance on surfaces, and then it introduces a new definition of medial structures, composing a bijection between medial structures and segments. Our method computes this bijection through a simple and fast iterative approach, and applies it to triangulated meshes.
Discrete Multi-Material Interface Reconstruction for Volume Fraction Data
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Anderson, John C.; Garth, C.; Duchaineau, Mark A.; Joy, Kenneth I.; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
We present the results from a user study looking at the ability of observers to mentally integrate wind direction and magnitude over a vector field. The data set chosen for the study is an MM5 (PSU/NCAR Mesoscale Model) simulation of Hurricane Lili over the Gulf of Mexico as it approaches the southeastern United States. Nine observers participated in the study. This study investigates the effect of layering on the observer's ability to determine the magnitude and direction of a vector field. We found a tendency for observers to underestimate the magnitude of the vectors and a counter-clockwise bias when determining the average direction of a vector field. We completed an additional study with two observers to try to uncover the source of the counter-clockwise bias. These results have direct implications to atmospheric scientists, but may also be able to be applied to other fields that use 2D vector fields.
Table of Contents and Cover
(The Eurographics Association and Blackwell Publishing Ltd, 2008)
Automatic Facsimile of Chinese Calligraphic Writings
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Xu, Songhua; Jiang, Hao; Jin, Tao; Lau, Francis C.M.; Pan, Yunhe
Articulated Object Reconstruction and Markerless Motion Capture from Depth Video
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Pekelny, Yuri; Gotsman, Craig
We present an algorithm for acquiring the 3D surface geometry and motion of a dynamic piecewise-rigid object using a single depth video camera. The algorithm identifies and tracks the rigid components in each frame, while accumulating the geometric information acquired over time, possibly from different viewpoints. The algorithm also reconstructs the dynamic skeleton of the object, thus can be used for markerless motion capture. The acquired model can then be animated to novel poses. We show the results of the algorithm applied to synthetic and real depth video.
A Screen Space Quality Method for Data Abstraction
(The Eurographics Association and Blackwell Publishing Ltd., 2008) Johansson, Jimmy; Cooper, Matthew; A. Vilanova, A. Telea, G. Scheuermann, and T. Moeller
The rendering of large data sets can result in cluttered displays and non-interactive update rates, leading to time consuming analyses. A straightforward solution is to reduce the number of items, thereby producing an abstraction of the data set. For the visual analysis to remain accurate, the graphical representation of the abstraction must preserve the significant features present in the original data. This paper presents a screen space quality method, based on distance transforms, that measures the visual quality of a data abstraction. This screen space measure is shown to better capture significant visual structures in data, compared with data space measures. The presented method is implemented on the GPU, allowing interactive creation of high quality graphical representations of multivariate data sets containing tens of thousands of items
Fast Soft Self-Shadowing on Dynamic Height Fields
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Snydre, John; Nowrouzezahrai, Derek
We present a new, real-time method for rendering soft shadows from large light sources or lighting environments on dynamic height fields. The method first computes a horizon map for a set of azimuthal directions. To reduce sampling, we compute a multi-resolution pyramid on the height field. Coarser pyramid levels are indexed as the distance from caster to receiver increases. For every receiver point and every azimuthal direction, a smooth function of blocking angle in terms of log distance is reconstructed from a height difference sample at each pyramid level. This function s maximum approximates the horizon angle. We then sum visibility at each receiver point over wedges determined by successive pairs of horizon angles. Each wedge represents a linear transition in blocking angle over its azimuthal extent. It is precomputed in the order-4 spherical harmonic (SH) basis, for a canonical azimuthal origin and fixed extent, resulting in a 2D table. The SH triple product of 16D vectors representing lighting, total visibility, and diffuse reflectance then yields the soft-shadowed result. Two types of light sources are considered; both are distant and low-frequency. Environmental lights require visibility sampling around the complete 360 azimuth, while key lights sample visibility within a partial swath. Restricting the swath concentrates samples where the light comes from (e.g. 3 azimuthal directions vs. 16-32 for a full swath) and obtains sharper shadows. Our GPU implementation handles height fields up to 1024 x 1024 in real-time. The computation is simple, local, and parallel, with performance independent of geometric content.

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