Short Papers 2008

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

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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.
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.
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.
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.
Physically Based Modeling of Ice with Bubbles
(The Eurographics Association, 2008) Madrazo, Carlos; Okada, Minoru; Katerina Mania and Eric Reinhard
Bubbles are an important characteristic that determine the appearance of ice. In this paper the authors propose a strategy in order to construct geometric representations of ice that integrates bubbles in an ice cube and visualize them. Bubble characteristics depend on the velocity of ice formation and levels of air concentration of water that in this paper are determined by simulating ice and bubble formation processes together. Simplified physics of heat transfer and a level set method are used in order to evolve the ice-water interface and a simplified model of bubbles as spheres is discussed. Experimental result shows that the shape of ice during formation resembles the one of actual ice. The algorithm has a potential to include more complex physics for better accuracy
Removing Artifacts Due To Frequency-Domain Processing of Light-Fields
(The Eurographics Association, 2008) Intwala, Chintan; Georgeiv, Todor; Katerina Mania and Eric Reinhard
In previous works, light-field capture has been analyzed in spatio-angular representation. A light-field camera samples the optical signal within a single photograph by multiplexing the 4D radiance onto the physical 2D surface of the sensor. Besides sampling the light field spatially, methods have been developed for multiplexing the radiance in the frequency domain by optically mixing different spatial and angular frequency components. The mathematical method for recovering the multiplexed spatial and angular information from the frequency representation is very straightforward. However, the results are prone to lots of artifacts due to limitations inherent to frequency-domain processing of images. In this paper, we try understand the characteristics of these artifacts. Furthermore, we study the effect and sources of artifacts that affect the quality of the results and present various methods for the removal of artifacts.
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.
Video Carving
(The Eurographics Association, 2008) Chen, Billy; Sen, Pradeep; Katerina Mania and Eric Reinhard
We present a technique for summarizing a video into a short segment, while preserving the important events in the original. While many techniques remove whole frames from the video stream when condensing it, we observe that these deleted frames need not come from a single time step. More generally, deleted frames are 'sheets' through the space-time volume. This leads to an algorithm whereby sheets are incrementally carved from the video cube to shorten the length of a video. The problem of finding these sheets is formulated as a min-cut problem, whose solution can be mapped to a sheet.We show results by creating short, viewable summaries of long video sequences.
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.
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.
A Novel Approach to Support Quality of Experience in Remote Visualization on Mobile Devices
(The Eurographics Association, 2008) Paravati, Gianluca; Sanna, Andrea; Lamberti, Fabrizio; Ciminiera, Luigi; Katerina Mania and Eric Reinhard
This paper proposes a novel approach to support Quality of Experience (QoE) in remote visualization on mobile devices. Image resolution, frame rate, compression ratio, color depth, and device throughput are simultaneously considered in order to provide users valuable visualization experiences. User requirements are used by a QoE manager to estimate values for the above parameters, thus providing an optimal usage of the network bandwidth. Experimental results show how the proposed methodology can efficiently support remote visualization on mobile devices such as Personal Digital Assistants and smartphones allowing the user to obtain satisfactory visualization sessions.
Recognition of Human Actions using Layered Hidden Markov Models
(The Eurographics Association, 2008) Perdikis, Serafeim; Tzovaras, Dimitrios; Strintzis, Michael Gerasimos; Katerina Mania and Eric Reinhard
Human activity recognition has been a major goal of research in the field of human - computer interaction. This paper proposes a method which employs a hierarchical structure of Hidden Markov Models (Layered HMMs) in an attempt to exploit inherent characteristics of human action for more efficient recognition. The case study concerns actions of the arms of a seated subject and depends on the assumption of a static office environment. The first layer of HMMs detects short, primitive motions with direct targets, while every upper layer processes the previous layer inference to recognize abstract actions of longer time granularities. The results demonstrate the efficiency, the tolerance on noise interpolation and the high degree of person - invariance of the method.
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.
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
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.
Physically-Based Interactive Sand Simulation
(The Eurographics Association, 2008) Pla-Castells, Marta; García-Fernandez, Ignacio; Martinez-Dura, Rafael J.; Katerina Mania and Eric Reinhard
The interactive simulation of 3D terrains has been approached from several perspectives. Due to the complexity of the system involved, most of the models proposed focus on a visually realistic animation of the scene, rather than on a physically-based accurate simulation of a granular system. Those models lack generality when interacting with the environment; in most cases, no reaction forces are computed, considering only soil deformation. This limitation reduces their usability in applications such as driving simulators. We propose the use of a theoretical discrete model that considers normal forces for 3D real-time simulation of granular systems. We also extend this model to consider horizontal forces, allowing a wider range of interactions. Several numerical tests have been implemented and detailed results have been analyzed which show a good model performance.
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.
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.
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.

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