Short Papers 2008

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

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Rendering Method for Flat Origami
(The Eurographics Association, 2008) Mitani, Jun; Katerina Mania and Eric Reinhard
In flat Origami (Origami which is folded flat), some cases exist that have a closed-loop in the overlap order of faces after they are folded. It is difficult to display this shape correctly on the screen when Origami is expressed by sets of plane polygons of zero thickness as is generally used in CG because all faces are placed on the same plane. In the present paper, we propose a new rendering technique to solve this problem. In the proposed method, we prepare a matrix that represents the overlap relation between two faces and a face ID buffer, the concept of which is similar to a Z buffer in the z-buffer algorithm. With this buffer, the face located in the uppermost is monitored in each pixel at the rendering stage. We render the shape on the face ID buffer using a scanline algorithm and display the folded shape by outputting the result in which the edges are extracted. Moreover, we render the shape in technical illustration style by coloring each vertex according to the number of mountain and valley folds connected to the vertex. In addition, we propose a simple pseudo shading algorithm.
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.
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.
Shadowed Relighting of Dynamic Geometry with 1D BRDFs
(The Eurographics Association, 2008) Nowrouzezahrai, Derek; Kalogerakis, Evangelos; Simari, Patricio; Fiume, Eugene; Katerina Mania and Eric Reinhard
We present a method for synthesizing the dynamic self-occlusion of an articulating character in real-time (> 170Hz) while incorporating reflection effects from 1D BRDFs under dynamic lighting and view conditions. We introduce and derive a general operator form for convolving spherical harmonics (SH) occlusion vectors with arbitrary 1D BRDF kernels. This operator, coupled with a compact linear model for predicting SH occlusion over articulating meshes, segments the BRDF and visibility terms of the direct illumination integral. We illustrate our results on a thin-membrane translucency model and the normalized Phong BRDF.
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 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.
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.
Post Facto Registration Tools for Urban Modelling
(The Eurographics Association, 2008) Morvan, Yann; Hinks, Tommy; Carr, Hamish; Laefer, Debra F.; O'Sullivan, Carol; Morrish, W. Sean; Katerina Mania and Eric Reinhard
Urban modelling applications require high-precision geometric models both for graphical rendering and for engineering purposes. While geometric models, photographic images and laser-scanned point clouds are ideally co-registered to national coordinate grids at the time of acquisition, the quantity and diversity of data sources means that registration must often be performed post facto. Moreover, the sheer size of urban point clouds prevents automated conversion and registration of the entire data set at once. We describe an interactive tool that manages the workflow for converting urban-scale point clouds to grid-registered geometric models. Our 'user in the loop' approach lets us leverage natural human understanding of the data to bypass issues of scale.
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.
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
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.
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.
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.
Real-Time Volumetric Tests Using Layered Depth Images
(The Eurographics Association, 2008) Trapp, Matthias; Doellner, Juergen; Katerina Mania and Eric Reinhard
This paper presents a new approach for performing efficiently 3D point-in-volume tests for solid and arbitrary complex shapes. It classifies a 3D point as inside or outside of a solid specified by 3D polygonal geometry. Our technique implements a basic functionality that offers a wide range of applications such as clipping, collision detection, interactive rendering of multiple 3D lenses as well as rendering using multiple styles. It is based on an extension of layered depth images (LDI) in combination with shader programs. An LDI contains layers of unique depth complexity and is represented by a 3D volume texture. The test algorithm transforms a 3D point into an LDI texture space and, then, performs ray marching through the depth layers to determine its classification. We show how to apply real-time volumetric tests to implement 3D clipping and rendering using multiple styles. In addition, we discuss limitations and possible improvements.
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.
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.
Mining Motifs from Human Motion
(The Eurographics Association, 2008) Meng, Jingjing; Yuan, Junsong; Hans, Mat; Wu, Ying; Katerina Mania and Eric Reinhard
Mining frequently occurring temporal motion patterns (motion motifs) is important for understanding, organizing and retrieving motion data. However, without any a priori knowledge of the motifs, such as their lengths, contents, locations and total number, it remains a challenging problem due to the enormous computational cost involved in analyzing huge motion databases. Moreover, since the same motion motif can exhibit different temporal and spatial variations, it prevents directly applying existing data mining methods to motion data. In this paper, we propose an efficient motif discovery method which can handle both spatial and temporal variations of motion data. We translate the motif discovery problem into finding continuous paths in a matching trellis, where each continuous path corresponds to an instance of a motif. A tree-growing method is introduced to search for the continuous paths constrained by a branching factor, and to accommodate intra-pattern variations of motifs. By using locality-sensitive hashing (LSH) to find the approximate matches and build the trellis, the overall complexity of our algorithm is only sub-quadratic to the size of the database, and is of linear memory cost. Experimental results on a data set of 32,260 frames show that our method can effectively discover meaningful motion motifs regardless of their spatial and temporal variations.
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.

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