Short Papers

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

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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.
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.
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.
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.
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.
Skeleton Computation of an Image Using a Geometric Approach
(The Eurographics Association, 2010) Martinez, Jonas; Vigo, Marc; Pla-Garcia, Nuria; Ayala, Dolors; H. P. A. Lensch and S. Seipel
In this work we develop two algorithms to compute the skeleton of a binary 2D image. Both algorithms follow a geometric approach and work directly with the boundary of the image which is an orthogonal polygon (OP). One of these algorithms processes the edges of the polygon while the other one uses its vertices. Compared with a thinning method, the presented algorithms show a good performance. This is a work in progress as our final goal is to extend the vertex-based algorithm method to 3D in order to compute the surface skeleton of a binary volume.
Sliding Deformation: Shape Preserving Per-Vertex Displacement
(The Eurographics Association, 2010) Pinskiy, Dmitriy; H. P. A. Lensch and S. Seipel
We present a novel algorithm for deforming a locally smooth polygonal mesh by sliding its vertices over the surface. This sliding deformation creates the visual appearance of texture animation without requiring an explicit global surface parameterization or the overhead of storing texture coordinates. The proposed deformation algorithm can also be employed to slide vertices over the surface to increase or decrease resolution in desired regions. To produce the sliding displacement, we define a deformation space that couples the precision of a local parameterization with the advantages of a global parameterization, needed for consistency of displacements over the affected region. On demand, we establish a set of local parameterization spaces that minimize distortion error around each displaced vertex. To propagate the displacement direction across the set of spaces while ensuring coherency, we calculate a representation of global direction in each local space. To map a displaced vertex from the deformation space back to the surface with minimal distortion, we use the local parameterization space of the given vertex. Our method is inherently parallelizable, works on arbitrary topology, and provides a user-friendly, intuitive interface.
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.
A Spatially Adaptive Morphological Filter for Dual-Resolution Interface Tracking of Fluids
(The Eurographics Association, 2010) Söderström, Andreas; Museth, Ken; H. P. A. Lensch and S. Seipel
We present a novel surface-tracking technique for free-surface fluid animations. Unlike the semi-implicit Particle Level Set method (PLS) our interface-tracking approach is purely implicit and hence avoids some of the well-known issues like surface noise and inflated memory footprints. Where PLS augments the interface with Lagrangian tracker-particles, we instead employ a higher resolution level set represented as a DT-Grid. The synchronization of our dual-resolution level sets is facilitated by a novel Spatially Adaptive Morphological (SAM) filter that attempts to preserve fine details while still avoiding spurious topology changes and boundary violations. We demonstrate that our approach can achieve comparative results to the PLS, but with a fraction of the memory footprint. We also show how our technique can be used to effectively enhance thin interface sheets at the cost of volume gain.
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.
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.
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.
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.
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 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.
Volumetric Hand Reconstructions for Non-verbal Communication in Shared Virtual Environments
(The Eurographics Association, 2010) John, Christoph; Regenbrecht, Holger; Schwanecke, Ulrich; H. P. A. Lensch and S. Seipel
Enhancing desk-based computer environments with virtual reality technology requires natural interaction support, in particular hand tracking and visualization. In shared virtual environments hand tracking does not only support interaction with the virtual environment, but also provides a channel for non-verbal communication. This paper presents a tabletop user interface and its integration into a three-dimensional teleconferencing system. Dense volume reconstructions of hands based on a probabilistic Shape from Silhouette algorithm are applied for tracking and visualization. The interface integration employs the derived probabilistic hand reconstructions to interactively generate mesh models characterized as isosurfaces of probabilistic volume data. It will be shown, that meshes resulting from probabilistic volume reconstructions thereby exhibit superior detail in comparison to mesh models generated from non-probabilistic comparative approaches which represent the current state of the art.
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.
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.
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.

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