Short Papers 2008

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https://diglib.eg.org/handle/10.2312/266

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Adaptive Remeshing of Non-Manifold Surfaces
(The Eurographics Association, 2008) Zilske, Michael; Lamecker, Hans; Zachow, Stefan; Katerina Mania and Eric Reinhard
We present a unified approach for consistent remeshing of arbitrary non-manifold triangle meshes with additional user-defined feature lines, which together form a feature skeleton. Our method is based on local operations only and produces meshes of high regularity and triangle quality while preserving the geometry as well as topology of the feature skeleton and the input mesh.
Artificial Mosaics by Gradient Vector Flow
(The Eurographics Association, 2008) Battiato, Sebastiano; Blasi, Gianpiero Di; Gallo, Giovanni; Guarnera, Giuseppe Claudio; Puglisi, Giovanni; Katerina Mania and Eric Reinhard
In this paper a novel approach for artificial mosaic generation is proposed. Gradient Vector Flow computation together with heuristics to maximise the covered mosaic area are used. The high frequency details are managed in a global way allowing to preserve the mosaic-style also for small ones. Experiments and comparisons with previous works confirm the effectiveness of the proposed algorithm.
Boolean Operations for Free-form Models Represented in Geometry Images
(The Eurographics Association, 2008) Fu, Yan; Zhou, Bingfeng; Katerina Mania and Eric Reinhard
We present a Boolean operation algorithm for free-form solid models represented in geometry images. By taking advantage of the regular data organization of geometry images, our algorithm can perform efficient surface division using boundary-fill algorithm which is previously used for digital image processing. A quadtree subdivision scheme is also applied to the geometry images to accelerate the intersection line calculation. Experimental result shows that the algorithm can generate well-defined closed triangle meshes for Boolean operations. The resulted triangle mesh can also be converted into a geometry image for further processing.
Compensation of the Light Attenuation with Depth of Images Captured by a Confocal Microscope Using a MRF Deformation Model and Graph Cuts
(The Eurographics Association, 2008) Capek, Martin; Michalek, Jan; Janacek, Jiri; Kubinova, Lucie; Hana, Karel; Smrcka, Pavel; Katerina Mania and Eric Reinhard
We study series of fluorescent optical sections, i.e. three-dimensional (3D) biomedical images, captured by a confocal laser scanning microscope (CLSM). Fluorescent image intensities of optical sections from deep layers of the specimen are often darker than intensities of sections from the top layers due to absorption and scattering of both excitation and fluorescent light. To solve this problem we apply a Markov Random Field (MRF) model including an efficient deformation model for tracking structures within the 3D images for computation of optical flow. We approach the corresponding optimization problem by the graph cuts. Image intensities of optical sections are recomputed according to the found optical flow, since the flow gives us evaluation of their proper brightness. Finally, the light attenuation with depth is compensated by matching accumulative histograms of optical sections of the original series with respect to optical sections improved by the optical flow. By this approach we obtain an algorithm that is less sensitive to changes of structures within series (especially to their enlargement and diminishing) than algorithms based purely on histogram matching, warping or equalization.
Contact Skinning
(The Eurographics Association, 2008) Duriez, Christian; Courtecuisse, Hadrien; Alcalde, Juan-Pablo de la Plata; Bensoussan, Pierre-Jean; Katerina Mania and Eric Reinhard
In this paper, we propose a new approach to model interactions through a skinning method. Skinning is a frequently used technique to animate a mesh based on skeleton motion. In the case of a hand motion sequence used to manipulate and grasp virtual objects, it is essential to accurately represent the contact between the virtual objects and the animated hand. To improve the level of realism, our approach allows to accurately solve friction contact laws. In addition, contact constraints defined on the surface of the hand can be applied onto the skeleton to produce plausible motion. We illustrate our work through two examples: the real-time simulation of a grasping task and a character animation based on motion capture.
Crowds in Context: Evaluating the Perceptual Plausibility of Pedestrian Orientations
(The Eurographics Association, 2008) Peters, Christopher; Ennis, Cathy; McDonnell, Rachel; O'Sullivan, Carol; Katerina Mania and Eric Reinhard
We describe a work-in-progress evaluating the plausibility of pedestrian orientations. While many studies have focused on creating accurate or fast crowd simulation models for populating virtual cities or other environments, little is known about how humans perceive the characteristics of generated scenes. Our initial study, reported here, consists of an evaluation based on static imagery reconstructed from annotated photographs, where the orientations of individuals have been modified. An important focus in our research is the consideration of the effects of the context of the scene on the evaluation, in terms of nearby individuals, objects and the constraints of the walking zone. This work could prove significant for improving and informing the creation of computer graphics pedestrian models. Our particular aim is to inform level-of-detail models
Efficient Soft Tissue Modelling Using Charged Particle Control Points
(The Eurographics Association, 2008) Buckley, Oliver; John, Nigel W.; Katerina Mania and Eric Reinhard
As the performance levels of personal computers increases so does the desire for more realistic and immersive software and simulation. An area where this is particularly the case is that of medical training simulation, where there is an increasing demand for high fidelity virtual environments. However, realistically modeling of soft tissue deformation still poses a considerable challenge especially when haptic feedback is required. This paper presents a new approach to soft tissue deformation using a novel Charged Particle method to control the haptic rendering while also adding a further level of realism by incorporating independent high resolution visualization to the simulation.
Efficient Spherical Harmonics Lighting with the Preetham Skylight Model
(The Eurographics Association, 2008) Habel, Ralf; Mustata, Bogdan; Wimmer, Michael; Katerina Mania and Eric Reinhard
We present a fast and compact representation of a skylight model for spherical harmonics lighting, especially for outdoor scenes. This representation allows dynamically changing the sun position and weather conditions on a per frame basis. We chose the most used model in real-time graphics, the Preetham skylight model, because it can deliver both realistic colors and dynamic range and its extension into spherical harmonics can be used to realistically light a scene. We separate the parameters of the Preetham skylight model s spherical harmonics extension and perform a polynomial two-dimensional non-linear least squares fit for the principal parameters to achieve both negligible memory and computation costs. Additionally, we execute a domain specific Gibbs phenomena suppression to remove ringing artifacts.
Efficient Visualization of Architectural Models from a Structure and Motion Pipeline
(The Eurographics Association, 2008) Farenzena, Michela; Fusiello, Andrea; Gherardi, Riccardo; Katerina Mania and Eric Reinhard
State of the art three dimensional reconstruction pipelines can nowadays produce models up to several million polygons without any human intervention from a set of digital images or video. Such models are able to stretch the rendering capabilities of current hardware. We propose to augment a typical structure from motion pipeline with two additional steps, automatic fitting of high-level solid primitives and relief maps extraction, thus recovering both the overall structure of a building and its fine geometry. This not only gives birth to a more tractable and semantic model of the imaged scene, but allows for efficient and compelling rendering. We substantiate our claims showing a complete example of the described system.
Evaluation of a Mobile MR Geovisualisation Interface
(The Eurographics Association, 2008) Liarokapis, Fotis; Katerina Mania and Eric Reinhard
This paper presents experimental results of a mobile mixed reality interface designed for geovisualization of 3D realistic urban environments which allows dynamic switching between three visualization domains: a virtual reality; an augmented reality and a mixed reality interface to get the best possible representation for visual exploration. On each domain, four different types of geovisualisation and navigation aids can be superimposed including georeferenced 3D maps, 2D digital maps, spatial 3D sound and 3D/2D textual annotations. Interaction is performed using keyboard, mouse, menus and tangible ways. To gather user requirements about urban and virtual navigation and to assess the effectiveness of mobile interface, a two-stage evaluation was performed.
FMDistance: A Fast and Effective Distance Function for Motion Capture Data
(The Eurographics Association, 2008) Onuma, Kensuke; Faloutsos, Christos; Hodgins, Jessica K.; Katerina Mania and Eric Reinhard
Given several motion capture sequences, of similar (but not identical) length, what is a good distance function? We want to find similar sequences, to spot outliers, to create clusters, and to visualize the (large) set of motion capture sequences at our disposal. We propose a set of new features for motion capture sequences. We experiment with numerous variations (112 feature-sets in total, using variations of weights, logarithms, dimensionality reduction), and we show that the appropriate combination leads to near-perfect classification on a database of 226 actions with twelve different categories, and it enables visualization of the whole database as well as outlier detection.
A Fragile Watermarking Scheme for Authentication of Semi-regular Meshes
(The Eurographics Association, 2008) Wang, Kai; Lavoue, Guillaume; Denis, Florence; Baskurt, Atilla; Katerina Mania and Eric Reinhard
This paper presents a fragile watermarking scheme for authentication of 3D semi-regular meshes. After one wavelet decomposition, the watermark is inserted by slightly modifying the norms and orientations of the obtained wavelet coefficient vectors. The inserted watermark is robust to the so-called content-preserving attacks including vertex reordering and similarity transformations. However, it is vulnerable to others attacks such as local and global geometric modifications and remeshing since the objective is to check the integrity of the mesh. Additionally, according to the watermark extraction result, these attacks can be precisely located on the surface of the attacked mesh in a blind way. Sufficient security level is also achieved by introducing secret keys and by using scalar Costa quantization scheme with appropriate parameter values. Experimental results demonstrate the efficacy of the proposed watermarking scheme.
Identification of Dynamic Mass Spring Parameters for Deformable Body Simulation
(The Eurographics Association, 2008) Lloyd, Bryn; Kirac, S.; Szekely, Gabor; Harders, Matthias; Katerina Mania and Eric Reinhard
Mass spring systems (MSS) are frequently used to simulate deformable objects because of their conceptual sim- plicity and computational speed. Unfortunately, the model parameters (spring coefficients, masses) are not related to material constitutive laws in an obvious way. In our earlier work we proposed a method, which can be used to relate the parameters of the MSS to constitutive models, often used in continuum mechanics. In this report we have used this strategy to develop new formulae for the dynamic MSS parameters, i.e. the masses and the damping coefficients. This is the first report which identifies the damper coefficients analytically. In this work we restrict our attention to triangular meshes. Experimental evidence is given in support of our results.
Improving Interaction Performance for Ray Tracing
(The Eurographics Association, 2008) Kurz, Daniel; Lux, Christopher; Springer, Jan P.; Froehlich, Bernd; Katerina Mania and Eric Reinhard
We have developed an approach for improving the performance of object manipulation in ray tracing systems. We assume that users alternate between navigating the scene and manipulating objects in the scene. We divide the scene in objects currently manipulated by the user and the non-interactive rest. Once a user stops navigating, we compute and store the first order reflections for the non-interactive objects. In a composition step only the manipulated objects need to be fully ray traced, while the stored reflections of the rest of the scene have to be tested only against the manipulated objects. In an initial evaluation we found that this approach significantly improves frame rates during object manipulation and thus increases interaction performance. Our approach directly extends to refraction and shadow rays. It could also be used for further ray generations beyond the first order effects, but the speedup would strongly depend on the actual scene and it would probably be less significant. Our approach is independent of the underlying spatial data structure and it neither reduces visual quality nor does it introduce visual artifacts within its constraints.
Interactive Stroke-Based NPR using Hand Postures on Large Displays
(The Eurographics Association, 2008) Grubert, Jens; Carpendale, Sheelagh; Isenberg, Tobias; Katerina Mania and Eric Reinhard
We explore the use of hand postures to interact with stroke-based rendering (SBR) on touch-sensitive large displays. In contrast to traditional WIMP interfaces, we allow people to directly engage with and influence a rendering. Our system allows the creation of new stroke primitives as well as provides mechanisms to distribute and then manipulate them on the canvas. We offer a set of natural mappings from hand postures to rendering parameterizations. The resulting system allows an intuitive exploration of SBR without the need for traditional desktop interfaces.
Knitty: 3D Modeling of Knitted Animals with a Production Assistant Interface
(The Eurographics Association, 2008) Igarashi, Yuki; Igarashi, Takeo; Suzuki, Hiromasa; Katerina Mania and Eric Reinhard
Knitty is an interactive design system for creating knitted animals. The user designs a 3D surface model using a sketching interface. The system automatically generates a knitting pattern and then visualizes the shape of the resulting 3D animal model by applying a simple physics simulation. The user can see the resulting shape before beginning the actual knitting. The system also provides a production assistant interface for novices. The user can easily understand how to knit each stitch and what to do in each step. In a workshop for novices, we observed that even children can design their own knitted animals using our system.
Laziness is a Virtue: Motion Stitching Using Effort Minimization
(The Eurographics Association, 2008) Li, Lei; McCann, James; Faloutsos, Christos; Pollard, Nancy; Katerina Mania and Eric Reinhard
Given two motion-capture sequences that are to be stitched together, how can we assess the goodness of the stitching? The straightforward solution, Euclidean distance, permits counter-intuitive results because it ignores the effort required to actually make the stitch. The main contribution of our work is that we propose an intuitive, first-principles approach, by computing the effort that is needed to do the transition (laziness-effort, or L-score ). Our conjecture is that, the smaller the effort, the more natural the transition will seem to humans. Moreover, we propose the elastic L-score which allows for elongated stitching, to make a transition as natural as possible. We present preliminary experiments on both artificial and real motions which show that our L-score approach indeed agrees with human intuition, it chooses good stitching points, and generates natural transition paths.
Level of Detail Flow Simulation
(The Eurographics Association, 2008) Klar, Gergely; Katerina Mania and Eric Reinhard
In this paper we present a framework to simulate visually plausible large scale flow of fluids or smoke. To maintain real-time speed, we define the simulation over a coarse grid which is refined with a more detailed grid at places where fine details may emerge, like around moving obstacles. The detailed grids also act as fixed frames of reference to the surrounded obstacles to prevent the need for working with moving boundaries in the flow.
Measuring and Enhancing the Legibility of GPU-rendered Text
(The Eurographics Association, 2008) Tycowicz, Christoph von; Loviscach, Joern; Katerina Mania and Eric Reinhard
Whereas the rendering of tiny typefaces in 2D applications has been perfected over decades, the legibility of text in 3D visualizations has rarely been addressed. This affects road signs, meters, screens, and books in virtual reality applications ranging from car driving simulators to digital lecture halls. To improve text rendering and display, we devised a lightweight psychovisual test to measure one prominent aspect of legibility. We subjected promising GPU-based methods for crisp minification to this test. It turned out that legibility may be improved without undue costs. Not all techniques whose results look appealing on first sight will, however, enhance legibility.
Microquad Soft Shadow Mapping Revisited
(The Eurographics Association, 2008) Schwarz, Michael; Stamminger, Marc; Katerina Mania and Eric Reinhard
Recently, real-time soft shadow research saw many important contributions from the class of soft shadow mapping algorithms, where approximate occluder geometry is reconstructed from a shadow map and backprojected onto the light source to determine its occlusion. An interesting approximation primitive is the microquad obtained from unprojected shadow map texel centers. However, its full potential has not yet been realized since correct clipping against the light and exact occlusion bitmask updates have previously been ignored motivated by performance considerations. In this paper, we first extend the microquad definition to also allow for triangles as micro-occluders. We then demonstrate how to determine the exact occlusion bitmask of a microquad with correct clipping.

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