Short Papers

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https://diglib.eg.org/handle/10.2312/279

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3D Isocontours Real-time Generation and Visualization of 3D Stepped Terrain Models
(The Eurographics Association, 2010) Glander, Tassilo; Trapp, Matthias; Döllner, Jürgen; H. P. A. Lensch and S. Seipel
Isocontours (also isopleths, isolines, level sets) are commonly used to visualize real-valued data defined over a 2D plane according to a set of given isovalues. To support the 3D landscape metaphor for information visualization, a 3D stepped terrain can be derived by lifting and extruding isolines to their particular isovalue, but typically requires triangulation of the resulting surface representation in a preprocessing step. We present a concept and rendering technique for triangle-based terrain models that provide interactive, adaptive generation and visualization of such stepped terrains without preprocessing. Our fully hardware-accelerated rendering technique creates additional step geometry for each triangle intersecting an iso-plane on-the-fly. Further, an additional interpolation schema facilitates smooth transition between established 3D terrain visualization and its stepped variant.
Adapting Precomputed Radiance Transfer to Real-time Spectral Rendering
(The Eurographics Association, 2010) Schwenk, Karsten; Franke, Tobias; Drevensek, Timm; Kuijper, Arjan; Bockholt, Ulrich; Fellner, Dieter W.; H. P. A. Lensch and S. Seipel
Spectral rendering takes the full visible spectrum into account when calculating light-surface interaction and can overcome the well-known deficiencies of rendering with tristimulus color models. We present a variant of the precomputed radiance transfer algorithm that is tailored towards real-time spectral rendering on modern graphics hardware. Our method renders diffuse, self-shadowing objects with spatially varying spectral reflectance properties under distant, dynamic, full-spectral illumination. To achieve real-time frame rates and practical memory requirements we split the light transfer function into an achromatic part that varies per vertex and a wavelengthdependent part that represents a spectral albedo texture map. As an additional optimization, we project reflectance and illuminant spectra into an orthonormal basis. One area of application for our research is virtual design applications that require relighting objects with high color fidelity at interactive frame rates.Spectral rendering takes the full visible spectrum into account when calculating light-surface interaction and can overcome the well-known deficiencies of rendering with tristimulus color models. We present a variant of the precomputed radiance transfer algorithm that is tailored towards real-time spectral rendering on modern graphics hardware. Our method renders diffuse, self-shadowing objects with spatially varying spectral reflectance properties under distant, dynamic, full-spectral illumination. To achieve real-time frame rates and practical memory requirements we split the light transfer function into an achromatic part that varies per vertex and a wavelengthdependent part that represents a spectral albedo texture map. As an additional optimization, we project reflectance and illuminant spectra into an orthonormal basis. One area of application for our research is virtual design applications that require relighting objects with high color fidelity at interactive frame rates.
Adaptive Collapsing on Bounding Volume Hierarchies for Ray-Tracing
(The Eurographics Association, 2010) Pinto, André Susano; H. P. A. Lensch and S. Seipel
Ray tracing is a computationally intensive process, several tree data structures and heuristics have been developed to optimize it. This paper presents a new heuristic in the area, based on collapsing some nodes in order to achieve a smaller expected number of node-tests. Two ways of using this heuristic in Bounding Volume Hierarchies are presented as well as the cost-model used to drive the heuristic development and measure it s efficiency. Some procedures on integrating this heuristic with other optimizations are also discussedRay tracing is a computationally intensive process, several tree data structures and heuristics have been developed to optimize it. This paper presents a new heuristic in the area, based on collapsing some nodes in order to achieve a smaller expected number of node-tests. Two ways of using this heuristic in Bounding Volume Hierarchies are presented as well as the cost-model used to drive the heuristic development and measure it s efficiency. Some procedures on integrating this heuristic with other optimizations are also discussed
Animating Sand as a Surface Flow
(The Eurographics Association, 2010) Zhu, Bo; Yang, Xubo; H. P. A. Lensch and S. Seipel
This paper presents a new efficient method for animating sand and other granular materials in 3D scenes. Our method couples 2D and 3D simulation techniques in a physically based way. A surface flow model of granular material-the BCRE model-is used to separate sand piles into two layers: a surface flowing layer and a static layer. The surface layer is simulated using discrete element method (DEM) to capture the detailed flowing behavior, while the invisible and static layer is represented by a height field for efficiency. The matter transfer between the two layers is modeled based on the surface flow equations through a particle interface. We demonstrate that our method leads to significant improvements of computational efficiency compared to standard discrete element method, without sacrificing the rich 3D animation effects.
Automatic Composition of Motion Capture Animation for Music Synchronization
(The Eurographics Association, 2010) Xu, Jianfeng; Takagi, Koichi; Kawada, Ryoichi; H. P. A. Lensch and S. Seipel
To enrich the music experience, automatic generation of a CG music visualizer is attracting more and more attention, where 3D animation is composed to synchronize with the music using motion capture data. In this paper, we present a novel approach for the above purpose, where both beat and intensity are employed to synchronize the motion with the music.We extend the conventional unstructured motion graphs to structured motion graphs (called weighted motion graphs) using motion beat and intensity, where a best path is searched by dynamic programming to obtain beat-level synchronization. Our objective function is designed for the following three aspects: motion quality, cost from beat synchronization, and cost from intensity synchronization. Our experiments with a user study demonstrate that the proposed approach can effectively generate attractive animations for music synchronization with much less computational cost than the state-of-the-art alternative.
Data-parallel Micropolygon Rasterization
(The Eurographics Association, 2010) Eisenacher, Christian; Loop, Charles; H. P. A. Lensch and S. Seipel
Abstract We implement a tile based sort-middle rasterizer in CUDA and study its performance characteristics when used as a backend for adaptive tessellation down to micropolygons. Tessellation and bucketing map very well to the data-parallel paradigm of CUDA, and the majority of time is spent with rasterization. Despite this, our fastest implementation is able to reach 30-50% of the hardware rasterization performance of an Nvidia GTX 280. Overall we are able to rasterize 4 M textured and Phong shaded microquads into a 1600x1200 framebuffer at 10-12 fps.Abstract We implement a tile based sort-middle rasterizer in CUDA and study its performance characteristics when used as a backend for adaptive tessellation down to micropolygons. Tessellation and bucketing map very well to the data-parallel paradigm of CUDA, and the majority of time is spent with rasterization. Despite this, our fastest implementation is able to reach 30-50% of the hardware rasterization performance of an Nvidia GTX 280. Overall we are able to rasterize 4 M textured and Phong shaded microquads into a 1600x1200 framebuffer at 10-12 fps.
Dynamic Cage-Driven 3D Range-Scan Alignment
(The Eurographics Association, 2010) Seversky, Lee M.; Yin, Lijun; H. P. A. Lensch and S. Seipel
This paper presents a novel and automatic approach for aligning range-scan data of objects exhibiting non-rigid, articulated motion using a cage-driven reduced deformable model. Reduced deformable models have previously been used for non-rigid registration. However, these approaches usually assume a model apriori or determine one in step with the registration which adds complexity. We choose a cage-based space deformation mapping as the reduced deformable model and formulate the scan alignment problem as a space deformation problem. This cagebased deformation mapping provides a compact deformation model which is inherently geometric. We seek the deformation of a source cage (and embedded geometry) that results in the best alignment of the source and target scans. The main advantage of our approach is that the reduced deformable model is constructed automatically from the underlying object geometry and is independent of the alignment procedure as it does not require explicit partitioning of the object into parts or the establishment of joints. Our alignment algorithm is completely automatic and does not require initial correspondences between the surfaces to be aligned.This paper presents a novel and automatic approach for aligning range-scan data of objects exhibiting non-rigid, articulated motion using a cage-driven reduced deformable model. Reduced deformable models have previously been used for non-rigid registration. However, these approaches usually assume a model apriori or determine one in step with the registration which adds complexity. We choose a cage-based space deformation mapping as the reduced deformable model and formulate the scan alignment problem as a space deformation problem. This cagebased deformation mapping provides a compact deformation model which is inherently geometric. We seek the deformation of a source cage (and embedded geometry) that results in the best alignment of the source and target scans. The main advantage of our approach is that the reduced deformable model is constructed automatically from the underlying object geometry and is independent of the alignment procedure as it does not require explicit partitioning of the object into parts or the establishment of joints. Our alignment algorithm is completely automatic and does not require initial correspondences between the surfaces to be aligned.
A Film Balloon Design System Integrated with Shell Element Simulation
(The Eurographics Association, 2010) Furuta, Yohsuke; Umetani, Nobuyuki; Mitani, Jun; Igarashi, Takeo; Fukui, Yukio; H. P. A. Lensch and S. Seipel
CAD systems that have user-friendly interfaces for assisting ordinary people to design objects is becoming common. Most of these systems combine a sketch interface with physical simulation. In this paper, we propose a system for designing balloons made of non-stretchy material such as aluminum foil, plastic film and paper. We implemented the system by using a finite element method that is based on discrete Kirchhoff triangle (DKT) shell elements and a sketch interface that enables users to easily design the realistic shape of an inflated balloon. The 2D pattern for the balloon design is generated automatically by our system. We evaluated our system by a user study with six elementary school children and their parents. These users designed target objects and responded to a questionnaire.
Finding Approximate Ambigrams and Making them Exact
(The Eurographics Association, 2010) Loviscach, Joern; H. P. A. Lensch and S. Seipel
Rotational ambigrams are arrangements of letters that can also be read upside down. Existing approaches to automatically create such ambigrams employ highly artificially-looking and difficult-to-read typefaces. In contrast to that, the ambigram generator introduced here is based on a vector graphics editor that ensures perfect symmetry. A major component is an algorithm to smoothly fuse different vector shapes. As not all words lend themselves to be converted into legible ambigrams, an optional preparatory step is included. In this step, a dictionary is searched for words that are shaped almost symmetrically so that meaningful input is provided to the editing stage.
gCubik+i Virtual 3D Aquarium: Interfacing a Graspable 3d Display with a Tabletop Display
(The Eurographics Association, 2010) Lopez-Gulliver, Roberto; Yoshida, Shunsuke; Makino, Mao; Yano, Sumio; Ando, Hiroshi; H. P. A. Lensch and S. Seipel
We propose gCubik+i as a new interactive platform that naturally interfaces a 3D display with a tabletop display. The proposed platform is suitable for group collaboration and it introduces two novel interaction paradigms to existing tabletop display applications: 1) natural switching between the shared working spaces of the table and the users hands; and 2) transforming static 2D images into interactive 3D images that can be viewed and manipulated as if holding a real object. This paper describes the conceptual design and prototype implementation of the gCubik+i platform along with a description of its 3D virtual aquarium application.
Hybrid Mesh Editing
(The Eurographics Association, 2010) Borosán, Péter; Howard, Reid; Zhang, Shaoting; Nealen, Andrew; H. P. A. Lensch and S. Seipel
Surface-based deformation and cage-based deformation are two popular shape editing paradigms. Surface-based methods are easy to use and produce high-quality results by preserving differential properties of the surface mesh, but are limited by their computational requirements. Cage-based methods produce results quickly but at the expense of usability and realism, and typically require manual construction of suitable cages. We introduce a hybrid approach that combines the two methods. The user can perform edits on an automatically-generated simplified version of an input shape using As-rigid-as-possible surface modeling, and the edit is propagated to the original shape by a precomputed space deformation based on Mean value coordinates. We analyze deformation quality and running time for a variety of cage sizes. High-quality results are obtained for meshes on the order of 100K vertices at interactive rates by using cages with app. 5% of the vertices of the original shape.
Interactive Creation of Virtual Worlds Using Procedural Sketching
(The Eurographics Association, 2010) Smelik, Ruben M.; Tutenel, Tim; Kraker, Klaas Jan de; Bidarra, Rafael; H. P. A. Lensch and S. Seipel
Procedural modelling is an attractive alternative to cut down the costs of manual content creation for virtual worlds. We discuss our declarative modelling approach to the creation of 3D virtual worlds, which integrates a variety of procedural techniques in order to enable a non-specialist user to interactively create a complete 3D virtual world in minutes. In particular, we introduce procedural sketching, a novel paradigm which allows designers to quickly specify and see the effects of their procedural modelling operations, and describe its main features as implemented in our prototype system SketchaWorld. Two main interaction modes are described, for specifying the landscape and terrain features, respectively. Our approach automatically fits all generated terrain features with their surroundings, for example by smoothing out rough terrain for roads, or creating a bridge to cross a river. It is concluded that this approach provides designers with the productivity gain of procedural methods, while still allowing for fine user control and actively supporting iterative modelling.
Interactive Rendering to View-Dependent Texture-Atlases
(The Eurographics Association, 2010) Trapp, Matthias; Döllner, Jürgen; H. P. A. Lensch and S. Seipel
The image-based representation of geometry is a well known concept in computer graphics. Due to z-buffering, the derivation of such representations using render-to-texture delivers only information of the closest fragments with respect to the virtual camera. Often, transparency-based visualization techniques, e.g., ghosted views, also require information of occluded fragments. These can be captured using multi-pass rendering techniques such as depthpeeling or stencil-routed A-buffers on a per-fragment basis. This paper presents an additional rendering technique that enables the derivation of image-based representations on a per-object level within a single rendering pass. We use a dynamic 3D texture atlas that is parameterized on a per-frame basis. Prior to rasterization, the primitives are transformed to their respective position within the texture atlas, using vertex-displacement in screen space.The image-based representation of geometry is a well known concept in computer graphics. Due to z-buffering, the derivation of such representations using render-to-texture delivers only information of the closest fragments with respect to the virtual camera. Often, transparency-based visualization techniques, e.g., ghosted views, also require information of occluded fragments. These can be captured using multi-pass rendering techniques such as depthpeeling or stencil-routed A-buffers on a per-fragment basis. This paper presents an additional rendering technique that enables the derivation of image-based representations on a per-object level within a single rendering pass. We use a dynamic 3D texture atlas that is parameterized on a per-frame basis. Prior to rasterization, the primitives are transformed to their respective position within the texture atlas, using vertex-displacement in screen space.
Path Regeneration for Interactive Path Tracing
(The Eurographics Association, 2010) Novák, Jan; Havran, Vlastimil; Dachsbacher, Carsten; H. P. A. Lensch and S. Seipel
Rendering of photo-realistic images at interactive frame rates is currently an extensively researched area of computer graphics.Many of these approaches attempt to utilize the computational power of modern graphics hardware for ray tracing based methods. When using path tracing algorithms the ray paths are highly incoherent, hence we propose an efficient technique that minimizes the divergence in execution flow and ensures full utilization by intelligently regenerating the paths. We analyze the conditions under which our improvements provide the highest speedup, and demonstrate the performance of the overall system by rendering interactive previews of global illumination solutions using (bidirectional) path tracing with progressive refinement.Rendering of photo-realistic images at interactive frame rates is currently an extensively researched area of computer graphics.Many of these approaches attempt to utilize the computational power of modern graphics hardware for ray tracing based methods. When using path tracing algorithms the ray paths are highly incoherent, hence we propose an efficient technique that minimizes the divergence in execution flow and ensures full utilization by intelligently regenerating the paths. We analyze the conditions under which our improvements provide the highest speedup, and demonstrate the performance of the overall system by rendering interactive previews of global illumination solutions using (bidirectional) path tracing with progressive refinement.
Procedural Descriptions of Anisotropic Noisy Textures by Example
(The Eurographics Association, 2010) Gilet, Guillaume; Dischler, Jean-Michel; Soler, Luc; H. P. A. Lensch and S. Seipel
This short paper introduces a new approach to automate the creation of procedural anisotropic noisy textures by using an example. As for past approaches that allow one to obtain procedural descriptions of stochastic textures, it uses a sum of multi-scale noise functions and a combined spectral / histogram-based approach. The improvement, here, consists in better controlling the spectral domain by using Gabor noise functions. This allows us to extend the range of textures that can be addressed, while bringing a number of advantages compared to classical examplebased texture synthesis: extreme compactness, continuous definition over infinite space, easy extension to solid (even animated solid) textures and straight texture value computation in the fragment shader.This short paper introduces a new approach to automate the creation of procedural anisotropic noisy textures by using an example. As for past approaches that allow one to obtain procedural descriptions of stochastic textures, it uses a sum of multi-scale noise functions and a combined spectral / histogram-based approach. The improvement, here, consists in better controlling the spectral domain by using Gabor noise functions. This allows us to extend the range of textures that can be addressed, while bringing a number of advantages compared to classical examplebased texture synthesis: extreme compactness, continuous definition over infinite space, easy extension to solid (even animated solid) textures and straight texture value computation in the fragment shader.
Ray Tracing using Hierarchies of Slab Cut Balls
(The Eurographics Association, 2010) Källberg, Linus; Larsson, Thomas; H. P. A. Lensch and S. Seipel
In this paper, bounding volume trees of slab cut balls are evaluated and compared with other types of trees for ray tracing. A novel tree construction algorithm is proposed, which utilizes a relative orientation heuristic between parent and child nodes. Also, a fast intersection test between a ray and a slab cut ball is presented. Experimental comparisons to other commonly used enclosing shapes reveal that the slab cut ball is attractive. In particular, the slab cut ball outperforms the sphere in all tested scenes with speed-up factors between 1 and 4.
Real-Time Ray Tracing Using Nvidia OptiX
(The Eurographics Association, 2010) Ludvigsen, Holger; Elster, Anne Cathrine; H. P. A. Lensch and S. Seipel
Modern GPUs with their several hundred cores and more accessible programming models are becoming attractive devices for compute-intensive applications. They are particularly well suited for applications, such as image processing, where the end result is intended to be displayed via the graphics card. One of the more versatile and powerful graphics techniques is ray tracing. However, tracing each ray of light in a scene is very computational expensive and have traditionally been preprocessed on CPUs over hours, if not days. In this paper, Nvidia s new OptiX ray tracing engine is used to show how the power of modern graphics cards, such as the Nvidia Quadro FX 5800, can be harnessed to ray trace several scenes that represent real-life applications in real-time speeds ranging from 20.63 to 67.15 fps. Near-perfect speedup is demonstrated on dual GPUs for scenes with complex geometries. The impact on ray tracing of the recently announced Nvidia Fermi processor, is also discussed.Modern GPUs with their several hundred cores and more accessible programming models are becoming attractive devices for compute-intensive applications. They are particularly well suited for applications, such as image processing, where the end result is intended to be displayed via the graphics card. One of the more versatile and powerful graphics techniques is ray tracing. However, tracing each ray of light in a scene is very computational expensive and have traditionally been preprocessed on CPUs over hours, if not days. In this paper, Nvidia s new OptiX ray tracing engine is used to show how the power of modern graphics cards, such as the Nvidia Quadro FX 5800, can be harnessed to ray trace several scenes that represent real-life applications in real-time speeds ranging from 20.63 to 67.15 fps. Near-perfect speedup is demonstrated on dual GPUs for scenes with complex geometries. The impact on ray tracing of the recently announced Nvidia Fermi processor, is also discussed.
Segmental Brush Synthesis with Stroke Images
(The Eurographics Association, 2010) Ando, Ryoichi; Tsuruno, Reiji; H. P. A. Lensch and S. Seipel
We present a new approach for synthesizing realistic brush strokes exploiting recent works of texture synthesis from stroke images. (See Figure 1). In our method, stroke images are automatically decomposed into a sequence of quad segments and stitched together along the path of user s input to produce final image. Numbers of methods using textures on digital painting have been explored; our usage of texture is novel in that the source image is typically a photo and the synthesis is fast enough to achieve realtime feedback. In contrast to previous methods, our approach allows a large variety of artistic brushes to be interactively simulated fairly so that unique media which haven t caught attention yet such as lipsticks or finger paint, are well reproduced. We shall show some artworks created using our method and demonstrate feasibility of our algorithm.We present a new approach for synthesizing realistic brush strokes exploiting recent works of texture synthesis from stroke images. (See Figure 1). In our method, stroke images are automatically decomposed into a sequence of quad segments and stitched together along the path of user s input to produce final image. Numbers of methods using textures on digital painting have been explored; our usage of texture is novel in that the source image is typically a photo and the synthesis is fast enough to achieve realtime feedback. In contrast to previous methods, our approach allows a large variety of artistic brushes to be interactively simulated fairly so that unique media which haven t caught attention yet such as lipsticks or finger paint, are well reproduced. We shall show some artworks created using our method and demonstrate feasibility of our algorithm.We present a new approach for synthesizing realistic brush strokes exploiting recent works of texture synthesis from stroke images. (See Figure 1). In our method, stroke images are automatically decomposed into a sequence of quad segments and stitched together along the path of user s input to produce final image. Numbers of methods using textures on digital painting have been explored; our usage of texture is novel in that the source image is typically a photo and the synthesis is fast enough to achieve realtime feedback. In contrast to previous methods, our approach allows a large variety of artistic brushes to be interactively simulated fairly so that unique media which haven t caught attention yet such as lipsticks or finger paint, are well reproduced. We shall show some artworks created using our method and demonstrate feasibility of our algorithm.
Simple and Robust Iterative Importance Sampling of Virtual Point Lights
(The Eurographics Association, 2010) Georgiev, Iliyan; Slusallek, Philipp; H. P. A. Lensch and S. Seipel
We present a simple and practical algorithm for importance sampling virtual point lights (VPLs) [Kel97], suitable for multi-pass rendering. During VPL distribution, a Russian roulette decision accepts each VPL proportionally to its estimated contribution to the final image. As a result, more VPLs are concentrated in areas that illuminate the visible parts of the scene, at the cost of a negligible performance overhead in the preprocessing phase. As VPLs are sampled independently and proportionally to their camera importance, the algorithm is trivial to parallelize and remains efficient for low sampling rates. We show that this sampling scheme is well suited to both well illuminated scenes as well as for difficult visibility conditions. Moreover, in contrast to bidirectional and Metropolis VPL sampling [SIMP06, SIP07], the algorithm is fast and very simple to implement, and uses a single Monte Carlo sampler, making it easier to maintain good stratification.We present a simple and practical algorithm for importance sampling virtual point lights (VPLs) [Kel97], suitable for multi-pass rendering. During VPL distribution, a Russian roulette decision accepts each VPL proportionally to its estimated contribution to the final image. As a result, more VPLs are concentrated in areas that illuminate the visible parts of the scene, at the cost of a negligible performance overhead in the preprocessing phase. As VPLs are sampled independently and proportionally to their camera importance, the algorithm is trivial to parallelize and remains efficient for low sampling rates. We show that this sampling scheme is well suited to both well illuminated scenes as well as for difficult visibility conditions. Moreover, in contrast to bidirectional and Metropolis VPL sampling [SIMP06, SIP07], the algorithm is fast and very simple to implement, and uses a single Monte Carlo sampler, making it easier to maintain good stratification.
Skeleton Based As-Rigid-As-Possible Volume Modeling
(The Eurographics Association, 2010) Zhang, Shaoting; Nealen, Andrew; Metaxas, Dimitris; H. P. A. Lensch and S. Seipel
Shape deformation and editing are important for animation and game design. Based on as-rigid-as-possible (ARAP) surface modeling, an efficient approach is proposed to approximately preserve the volume of an object with large-scale deformations. The classical ARAP surface modeling uses two-stage iterations to recover rotations and preserve edge lengths. However, there is no volume preserving constraint, which may cause undesired artifacts. We show that the volume can be roughly kept by leveraging the skeleton information. First a skeleton is selected, and points are evenly generated on the skeleton. Then each point is correlated with several vertices on the surface of the object. The connectivity between the skeleton and the surface is defined as skeleton edges, which can be easily added into the linear system of the ARAP method as additional rows without breaking the manifoldness or sacrificing speed. Since this linear system is able to preserve the lengths of both the surface and skeleton edges, the area of cross sections and the volume between cross sections can be approximately preserved. In our experiments, we show that the rotations are natural and volumes are roughly kept. The system achieves real time performance for surface meshes with 5k vertices.

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