# GRAPP 2013 Abstracts

## Area 1 - Geometry and Modeling

Full Papers
Paper Nr: 34
Title:

### Rotationally Invariant 3D Shape Contexts using Asymmetry Patterns

Authors:

#### Federico M. Sukno, John L. Waddington and Paul F. Whelan

Abstract: This paper presents an approach to resolve the azimuth ambiguity of 3D Shape Contexts (3DSC) based on asymmetry patterns. We show that it is possible to provide rotational invariance to 3DSC at the expense of a marginal increase in computational load, outperforming previous algorithms dealing with the azimuth ambiguity. We build on a recently presented measure of approximate rotational symmetry in 2D defined as the overlapping area between a shape and rotated versions of itself to extract asymmetry patterns from a 3DSC in a variety of ways, depending on the spatial relationships that need to be highlighted or disabled. Thus, we define Asymmetry Patterns Shape Contexts (APSC) from a subset of the possible spatial relations present in the spherical grid of 3DSC; hence they can be thought of as a family of descriptors that depend on the subset that is selected. This provides great flexibility to derive different descriptors. We show that choosing the appropriate spatial patterns can considerably reduce the errors obtained with 3DSC when targeting specific types of points.

Paper Nr: 40
Title:

### An Efficient Alternative to Compute the Genus of Binary Volume Models

Authors:

#### Irving Cruz-Matías and Dolors Ayala

Abstract: In this paper we present a method to compute the Euler characteristic (χ) and the genus of a volume dataset. It uses an alternative decomposition model to represent binary volume datasets: the Compact Union of Disjoint Boxes (CUDB). The method is derived from the classical method used with a voxel model and the computation of c and the genus is achieved by analyzing the connectivity among boxes and using a CUDB connectedcomponent labeling process. We have tested our method both with phantom and real datasets and we show that it is more efficient than previous methods based on the voxel model, and other alternative models.

Paper Nr: 42
Title:

### A GPU-based Method for Generating quasi-Delaunay Triangulations based on Edge-flips

Authors:

#### Cristobal A. Navarro, Nancy Hitschfeld-Kahler and Eliana Scheihing

Abstract: The Delaunay edge-flip technique is a practical method for transforming any existing triangular mesh S into a mesh T(S) that satisfies the Delaunay condition. In this paper we present an iterative GPU-based method capable of improving triangulations under the Delaunay criteria. This method is based on the edge-flip technique and its implementation is fully integrable with the OpenGL rendering pipeline. Since the algorithm uses an e value to handle co-circular or close to co-circular point configurations, we can not guarantee that all triangles fulfill the Delaunay condition. However, we have compared the triangulations generated by our method with the ones generated by the Triangle software and by the CGAL library and we obtained less than 0.05% different triangles. Based on our experimental results, we report speedups from 14× to 50× against Lawson’s sequential algorithm and of approximately 3× against the O(nlog n) CGAL’s and Triangle’s constructive algorithms while processing bad quality triangulations.

Paper Nr: 45
Title:

### Parametric Curve Reconstruction from Point Clouds using Minimization Techniques

Authors:

#### Oscar E. Ruiz, C. Cortés, M. Aristizábal, Diego A. Acosta and Carlos A. Vanegas

Abstract: Curve reconstruction from noisy point samples is central to surface reconstruction and therefore to reverse engineering, medical imaging, etc. Although Piecewise Linear (PL) curve reconstruction plays an important role, smooth (C^1-, C^2-,...) curves are needed for many applications. In reconstruction of parametric curves from noisy point samples there remain unsolved issues such as (1) high computational expenses, (2) presence of artifacts and outlier curls, (3) erratic behavior of self-intersecting curves, and (4) erratic excursions at sharp corners. Some of these issues are related to non-Nyquist (i.e. sparse) samples. In response to these shortcomings, this article reports the minimization-based fitting of parametric curves for noisy point clouds. Our approach features: (a) Principal Component Analysis (PCA) pre-processing to obtain a topologically correct approximation of the sampled curve. (b) Numerical, instead of algebraic, calculation of roots in point-to-curve distances. (c) Penalties for curve excursions by using point cloud – to - curve and curve – to – point cloud. (d) Objective functions which are economic to minimize. The implemented algorithms successfully deal with self - intersecting and / or non-Nyquist samples. Ongoing research includes self-tuning of the algorithms and decimation of the point cloud and the control polygon.

Paper Nr: 55
Title:

### A Low Cost Visual Hull based Markerless System for the Optimization of Athletic Techniques in Outdoor Environments

Authors:

#### A. El-Sallam, M. Bennamoun, F. Sohel, J. Alderson, A. Lyttle and T. Warburton

Abstract: We propose a low cost 3D markerless motion analysis system for the optimization of athletic performance during training sessions. The system utilizes eight calibrated and synchronized High Definition (HD) cameras in order to capture a video of an athlete from different viewpoints. An improved kernel density estimation (KDE) based background segmentation algorithm is proposed to segment the athlete’s silhouettes from their background in each video frame. The silhouettes are then reprojected to reconstruct the 3D visual hull (VH) of the athlete. The center of the VH as an approximate representation of the body center of mass is then tracked over a number of frames. A set of motion analysis parameters are finally estimated and compared to the ones obtained by an outdoor state of the art marker-based system (Vicon). The proposed system is aimed at sports such as javelin, pole vault, and long jump and was able to provide comparable results with the Vicon system.

Paper Nr: 76
Title:

### A Graph-based Software Tool for the CAD Modeling of Mechanical Assemblies

Authors:

#### Stanislao Patalano, Ferdinando Vitolo and Antonio Lanzotti

Abstract: The challenge of reducing designing time for new mechanical assemblies, especially in the context of large companies, encourages the use of methods and tools aimed to support designing activities and to re-use the company know-how. Furthermore, the design choices must be rapidly check to avoid errors that could cause delay or expensive re-designing. In such a context, the graph theory and related algorithms could be used to define a transfer function, easily to implement, that governs a software tool able to support the designing activities. Therefore, the paper presents a designing approach, based on the graph theory, aimed to generate the geometric modeling of mechanical assemblies. The approach and the software tool are useful both for designer and companies that want to customize and improve such activities. Finally, the paper shows the case study related to the design of a transversal manual gearbox and the generation of a GUI, developed in MatLAB® environment, to validate the approach.

Short Papers
Paper Nr: 16
Title:

### Musculoskeletal System Modelling - Interpolation Method for Muscle Deformation

Authors:

#### Jana Hájková and Josef Kohout

Abstract: In this paper we present an interpolation method that was derived from the muscle deformation algorithm computed on the gradient domain deformation technique. The method uses linear constraints to preserve the local shape of the muscle and the non-linear volume constraints to preserve the volume of the mesh. The Gauss-Newton method with Lagrange multipliers is used as the main computation algorithm and the inter-polation approach serves especially to smooth up deformation steps. Thanks to the interpolation of main bones movement positions by several temporally interpositions, the large distances are optimized and the muscles of the musculoskeletal model are deformed in a more realistic way. The method was implemented in C++ language, using VTK framework and was integrated into the human body framework. Despite the fact that the current implementation is not optimised, all muscles tested were processed in a few minutes on commodity hardware, which is much faster in comparison with the traditional FEM approaches.

Paper Nr: 32
Title:

### Surface Mesh Qualities

Authors:

#### Marco Attene

Abstract: 3D surface models are often stored as indexed face sets, whereas algorithms can typically treat only a subset of the so-representable surfaces. Besides this gap between “potential” input and “allowed” input, more and more algorithms specify their input requirements at a high level of abstraction (e.g. “natural” shapes), and this makes it difficult to automatically assess the appropriateness of a specific model. In this article, surface meshes are analyzed in terms of indexed face sets and are characterized based on a collection of “qualities”. Qualities of a surface mesh represent the peculiarities of both the surface and its combinatorial representation, can be combined to formally define input requirements of algorithms, can be exploited to effectively estimate high-level categorizations of 3D objects in a collection, and can be used to quickly produce benchmarks for geometry processing algorithms starting from unstructured digital libraries.

Paper Nr: 37
Title:

### TriSI: A Distinctive Local Surface Descriptor for 3D Modeling and Object Recognition

Authors:

#### Yulan Guo, Ferdous Sohel, Mohammed Bennamoun , Min Lu and Jianwei Wan

Abstract: Local surface description is a critical stage for surface matching. This paper presents a highly distinctive local surface descriptor, namely TriSI. From a keypoint, we first construct a unique and repeatable local reference frame (LRF) using all the points lying on the local surface. We then generate three spin images from the three coordinate axes of the LRF. These spin images are concatenated and further compressed into a TriSI descriptor using the principal component analysis technique. We tested our TriSI descriptor on the Bologna Dataset and compared it to several existing methods. Experimental results show that TriSI outperformed existing methods under all levels of noise and varying mesh resolutions. The TriSI was further tested to demonstrate its effectiveness in 3D modeling. Experimental results show that it can accurately perform pairwise and multiview range image registration. We finally used the TriSI descriptor for 3D object recognition. The results on the UWA Dataset show that TriSI outperformed the state-of-the-art methods including spin image, tensor and exponential map. The TriSI based method achieved a high recognition rate of 98.4%.

Paper Nr: 38
Title:

### A Unified Spectral Embedding for Shape Correspondence

Authors:

#### Zizhao Wu, Ruyang Shou and Xinguo Liu

Abstract: Spectral embedding, as one of shape representative techniques, takes hold of many researchers’ attention in field of shape correspondence. One of the biggest challenges of spectral correspondence method is that embeddings of different shapes need to be aligned in the embedding space in order to eliminate sign flip and ordering ambiguity of their eigenfunctions, before seeking for correspondence. In this paper, we introduce a spectral correspondence method by embedding shapes in a unified space simultaneously. In the unified embedding space, the sample points of the same shape with small intrinsic distances, and from different shapes with high similarity, are close to each other. Our unified embedding can be used for correspondence directly, without need of alignment. Furthermore, the unified embedding captures both the spatial arrangement and the feature similarity. Shape correspondence is achieved with such embedding by minimizing an objective function. Results show the efficiency of our method.

Paper Nr: 64
Title:

### A Compact Representation for Topological Decompositions of Non-manifold Shapes

Authors:

#### David Canino and Leila De Floriani

Abstract: Simplicial complexes are extensively used for discretizing digital shapes in several applications. A structural description of a non-manifold shape can be obtained by decomposing the input shape into a collection of meaningful components with a simpler topology. Here, we consider a unique decomposition of a non-manifold shape into nearly manifold parts, known as the \emph{Manifold-Connected decomposition}, that we extend in arbitrary dimension. We present the \emph{Compact MC-Graph}, an efficient and graph-based representation for this decomposition, which can be combined with any topological data structure for encoding the underlying components. We present the main properties of this representation as well as algorithms for its generation. We also show that this representation may be more compact than many topological data structures, which do not explicitly describe the non-manifold structure of a shape.

Posters
Paper Nr: 46
Title:

### Cage-free Spatial Deformations

Authors:

#### M. Àngels Cerveró, Àlvar Vinacua and Pere Brunet

Abstract: We propose a new deformation scheme for polygonal meshes through generalized barycentric coordinates that does not require any explicit cage definition. Our system infers the connectivity of the control points defined by the user and computes the coordinates using this structure. This allows the user to incrementally position the control points (or delete them) wherever he considers more suitable. This freedom gives more control, precision and locality to the deformation process.

Paper Nr: 69
Title:

### Determination of Force Fields for Ode-based and Skeleton Driven Character Animation

Authors:

#### L. H. You, X. S. Yang, X. Jin, E. Chaudhry and Jian J. Zhang

Abstract: In the existing work, character modelling and animation are two separate tasks. After a character model is built, a lot of time and efforts are still required to animate the character model. Ordinary differential equation-based surface modelling and animation using physically based deformable curves to define and deform skin surfaces of 3D character models. With such a technique, character modelling and animation can be integrated into a unified framework by introducing time-dependent varying force fields into ordinary differential equations. This paper addresses the issue of determination of the force fields and proposes three models, i. e. linear transformation model, interpolation model and extrapolation model, to obtain time-dependent varying force fields. Some application examples are presented which demonstrates the force fields obtained from the three models create believable skin deformations of character models.

Paper Nr: 71
Title:

### Character Modeling using Physically based Deformable Curves

Authors:

#### L. H. You, E. Chaudhry, X. Jin, X. S. Yang and Jian J. Zhang

Abstract: Curve and physically based surface modelling techniques are becoming more and more active in geometric modelling of three-dimension (3D) objects since the former can create 3D models easily and quickly and the latter can produce more realistic appearances. In this paper, we present a curve and physically based surface modelling technique to create 3D models of virtual characters. This technique is based on physically based curve deformation. With such a technique, a character model is created from a number of surface patches. Each surface patch is obtained from physically based deformable curves. We introduce sculpting forces into a vector-valued ordinary differential equation to control the physically based deformations of curves. By describing concentrated sculpting forces with a sine series, we present an efficient analytical solution of the ordinary differential equation which can determine physically based curve deformations quickly. An example of character modelling is presented to demonstrate the application of our proposed technique.

Paper Nr: 85
Title:

### Statistical Analysis of Joint Determination for Skeleton Driven Animation of Human Hands

Authors:

#### E. Chaudhry, L. H. You, X. Jin and Jian J. Zhang

Abstract: Skeleton driven character animation is the most popular animation technique. It has been widely applied in the current computer animation industry. Correct determination of joint positions plays a very important role in creating realistic skin deformation of character animation. Current various approaches of skeleton driven character animation have not addressed this issue. In this paper, we propose a statistical method to determine the correct joint position using the statistical data analysis of different X-ray joint images. First, we measure different joint positions from sample X-ray images. Then, we statistically analyse the data, and obtain relative mean and maximum and minimum positions together with the relative range of joints which are used to determine correct joint positions.

## Area 2 - Rendering

Full Papers
Paper Nr: 25
Title:

### Hierarchical Design of Continuous Line Illustrations

Authors:

#### Fernando J. Wong and Shigeo Takahashi

Abstract: A hierarchical approach for designing continuous line illustrations, drawings that consist of a single line, is presented throughout this paper. Users specify a graph that will guide the overall shape of the line illustration, and proceed to assign a series of child graphs to many of its vertices. A line illustration can then be generated by taking all of these graphs into account, allowing us to produce complex drawings that are composed of several objects. Our approach also allows us to preserve the overall structure and orientation of the line as graphs are inserted or removed from the illustration. We also propose a variety of visual enhancements for our illustrations based on the specified hierarchical graph information and provide several result examples that demonstrate the effectiveness of our approach.

Paper Nr: 44
Title:

### GPU Cost Estimation for Load Balancing in Parallel Ray Tracing

Authors:

#### Biagio Cosenza, Carsten Dachsbacher and Ugo Erra

Abstract: Interactive ray tracing has seen enormous progress in recent years. However, advanced rendering techniques requiring many million rays per second are still not feasible at interactive speed, and are only possible by means of highly parallel ray tracing. When using compute clusters, good load balancing is crucial in order to fully exploit the available computational power, and to not suffer from the overhead involved by synchronization barriers. In this paper, we present a novel GPU method to compute a cost map: a per-pixel cost estimate of the ray tracing rendering process. We show that the cost map is a powerful tool to improve load balancing in parallel ray tracing, and it can be used for adaptive task partitioning and enhanced dynamic load balancing. Its effectiveness has been proven in a parallel ray tracer implementation tailored for a cluster of workstations.

Paper Nr: 50
Title:

### FlexRender: A Distributed Rendering Architecture for Ray Tracing Huge Scenes on Commodity Hardware

Authors:

#### Bob Somers and Zoë J. Wood

Abstract: As the quest for more realistic computer graphics marches steadily on, the demand for rich and detailed imagery is greater than ever. However, the current "sweet spot" in terms of price, power consumption, and performance is in commodity hardware. If we desire to render scenes with tens or hundreds of millions of polygons as cheaply as possible, we need a way of doing so that maximizes the use of the commodity hardware that we already have at our disposal. We propose a distributed rendering architecture based on message-passing that is designed to partition scene geometry across a cluster of commodity machines, allowing the entire scene to remain in-core and enabling parallel construction of hierarchical spatial acceleration structures. The design uses feed-forward, asynchronous messages to allow distributed traversal of acceleration structures and evaluation of shaders without maintaining any suspended shader execution state. We also provide a simple method for throttling work generation to keep message queueing overhead small. The results of our implementation show roughly an order of magnitude speedup in rendering time compared to image plane decomposition, while keeping memory overhead for message queuing around 1%.

Paper Nr: 51
Title:

### Interactive Rendering of Complex 3D-Treemaps with a Comparative Performance Evaluations

Authors:

#### Matthias Trapp, Sebastian Schmechel and Jürgen Döllner

Abstract: 3D-Treemaps are an important visualization technique for hierarchical views. In contrast to 2D-Treemaps, height can be used to map one additional attribute of the data items. Using the Treemap technique in combination with large datasets (more than 500k) a fast rendering and interaction techniques that are beyond collapsing/uncollapsing nodes is still one of the main challenges. This paper presents a novel rendering technique that enables the image synthesis of geometrical complex 3D-Treemaps in real-time. The fully hardware accelerated approach is based on shape generation using geometry shaders. This approach offers increased rendering performance and low update latency compared to existing techniques and through it enables new real-time interaction techniques to large datasets.

Short Papers
Paper Nr: 4
Title:

### Complex Plane Transformations for Manipulation and Visualization of Panoramas

Authors:

#### Leonardo Sacht and Luiz Velho

Abstract: We present a method for manipulation and visualization of wide-angle images using transformations defined on the complex plane C. We map the unit sphere S2 to C using the stereographic projection, multiply the complex plane by a given complex number, and map the result back to the sphere using the inverse of the stereographic projection. Since all these transformations preserve angle, we obtain a result containing only distortions due to the latitude/longitude representation of the sphere, which were already present in the input image. We then explore the possibility given by our technique of mapping wide fields of view to narrower ones. This makes possible to apply perspective projection to wider fields of view, leading to a natural generalization of the perspective projection in the context of panoramic images. Our results are generated in real-time and compare competitively with state-of-the-art methods used to project the viewing sphere to the image plane.

Paper Nr: 70
Title:

### Statistical Inverse Lighting

Authors:

#### Eduardo Fernández and Gonzalo Besuievsky

Abstract: Inverse lighting techniques allows to obtain the unknown light sources parameters, such as light position or flux emission, from desired lighting intentions. In this paper we present a new inverse lighting technique that uses the statistical mean and variance of the illuminated scene to obtain optimal solutions for a given lighting intention. This technique allows to explore a huge number of full radiosity solutions in a short time, reducing in this way drastically the optimization time required.

Paper Nr: 78
Title:

### Generalized Haptic Relief Atlas for Rendering Surface Detail

Authors:

#### Victor Theoktisto, Marta Fairen and Isabel Navazo

Abstract: A fast global approach that encodes haptic surface relief detail using an image-based Hybrid Rugosity Mesostructure Atlas (HyRMA) shell is presented. It is based on a depth/normal texture computed from surface differences of the same mesh object at different resolutions (a dense one with thousands/millions of triangles, and a highly decimated version). Per-face local depth differences are \emph{warped} from volume space into tangent space, and stored in a sorted relief atlas. Next, the atlas is sampled by a vertex/fragment shader pair, \emph{unwarped}, displacing the pixels at each face of the decimated mesh to render the original mesh detail with quite fewer triangles. We achieve accurate correspondence between visualization of surface detail and perception of its fine features without compromising rendering framerates, with some loss of detail at mesostructure holes''.

Paper Nr: 84
Title:

### Integrating Occlusion Culling and Hardware Instancing for Efficient Real-time Rendering of Building Information Models

Authors:

#### Mikael Johansson

Abstract: This paper presents an efficient approach for integrating occlusion culling and hardware instancing. The work is primarily targeted at Building Information Models (BIM), which typically share characteristics addressed by these two acceleration techniques separately – high level of occlusion and frequent reuse of building components. Together, these two acceleration techniques complement each other and allows large and complex BIMs to be rendered in real-time. Specifically, the proposed method takes advantage of temporal coherence and uses a lightweight data transfer strategy to provide an efficient hardware instancing implementation. Compared to only using occlusion culling, additional speedups of 1.25x-1.7x is achieved for rendering large BIMs received from real-world projects. These speedups are measured in viewpoints that represents the worst case scenarios in terms of rendering performance when only occlusion culling is utilized.

Posters
Paper Nr: 20
Title:

### Rendering Synthetic Objects into Full Panoramic Scenes using Light-depth Maps

Authors:

#### Aldo René Zang, Dalai Felinto and Luiz Velho

Abstract: This photo realistic rendering solution address the insertion of computer generated elements in a captured panorama environment. This pipeline supports productions specially aiming at spherical displays (e.g., fulldomes). Full panoramas have been used in computer graphics for years, yet their common usage lays on environment lighting and reflection maps for conventional displays. With a keen eye in what may be the next trend in the filmmaking industry, we address the particularities of those productions, proposing a new representation of the space by storing the depth together with the light maps, in a full panoramic light-depth map. Another novelty in our rendering pipeline is the one-pass solution to solve the blending of real and synthetic objects simultaneously without the need of post processing effects.

## Area 3 - Animation and Simulation

Full Papers
Paper Nr: 13
Title:

### Hybrid Particle Lattice Boltzmann Shallow Water for Interactive Fluid Simulations

Authors:

#### Jesus Ojeda and Antonio Susín

Abstract: We introduce a hybrid approach for the simulation of fluids based in the Lattice Boltzmann Method for Shallow Waters and particle systems. Our modified LBM Shallow Waters can handle arbitrary underlying terrain and arbitrary fluid depth. It also introduces a novel and simplified method of tracking dry-wet regions. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle, as breaking waves, are detected and automatically turned into splash particles. Albeit we use a simple ballistic particle system, our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, yet dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on commodity hardware.

Paper Nr: 18
Title:

### A Statistical Model for Coupled Human Shape and Motion Synthesis

Authors:

#### Alina Kuznetsova, Nikolaus F. Troje and Bodo Rosenhahn

Abstract: Due to rapid development of virtual reality industry, realistic modeling and animation is becoming more and more important. In the paper, we propose a method to synthesize both human appearance and motion given semantic parameters, as well as to create realistic animation of still meshes and to synthesize appearance based on a given motion. Our approach is data-driven and allows to correlate two databases containing shape and motion data. The synthetic output of the model is evaluated quantitatively and in terms of visual plausibility.

Paper Nr: 53
Title:

### Adaptively Simulating Inhomogeneous Elastic Deformation

Authors:

#### Sei Imai, Yonghao Yue, Bing-Yu Chen and Tomoyuki Nishita

Abstract: In this paper, we present an adaptive approach for simulating elastic deformation of homogeneous and inhomogeneous objects based on continuum mechanics. In typical adaptive simulation approaches, the deforming elastic object is usually subdivided to form a tree structure on the fly. However, they are not directly applicable for inhomogeneous elastic deformation, since the elasticity matrix, which describes the stiffness, of each element in each resolution is difficult to estimate at runtime. Furthermore, as most multi-resolution approaches, it is usually required that the stiffness of the object should either be uniform all throughout its body or consist of a collection of uniform parts, otherwise the elasticity matrices for the elements in coarse levels cannot be determined. Hence, we propose a bottom-up sampling approach to estimate the elasticity matrices for all elements in all levels based on a given stiffness function. Moreover, the subdivision process is also moved to the off-line preprocessing stage with the elasticity matrix estimation to reduce the runtime computational cost while achieving the adaptive simulation by adaptively selecting the simulation level on the fly. Therefore, we can efficiently simulate the deformation of an elastic object even with spatially varying stiffness.

Short Papers
Paper Nr: 33
Title:

### The Case for Physics Visualization in an Animator’s Toolset

Authors:

#### Ari Shapiro and Andrew W. Feng

Abstract: By associating physical properties with a digital character’s joint and bones, we are able to visualize explicitly a number of properties that can help animators develop high-quality animation. For example, proper ballistic arcs can be shown to demonstrate proper timing and location of a character during flight. In addition, a center of mass that accurately reflects the posture of the character can be shown to help with a balanced appearance during walking or running. In addition, motion properties not previously considered, such as angular momentum, can be easily identified when blatantly violated by an animator. However, very few inhouse or commercial system employ such tools, despite their nearly transparent use in an animator’s workflow and their utility in generating better-quality motion. In this paper, we argue the case for incorporating such toolset, describe an algorithm for implementing the tools, and detail that types of uses for such a tool.

Paper Nr: 36
Title:

### Directable Animation of Non-photorealistic Fluids

Authors:

#### Viraj Churi, Gaurav Bhagwat and Parag Chaudhuri

Abstract: This paper presents a method to control and direct a physically-based fluid simulation with user defined strokes. Strokes are interpreted as flowlines and introduce a smooth velocity field in their vicinity that allows the fluid simulation to be easily directed by an animator. We also allow the fluid to interact with arbitrarily shaped obstacles and have variable viscosity during the simulation. The strokes can be alive for a finite duration and are registered to a timeline to give keyframing like control to the animator over the physics driven simulation.

Paper Nr: 59
Title:

### Virtual Avatars Signing in Real Time for Deaf Students

Authors:

#### Lucía Vera, Inmaculada Coma, Julio Campos, Bibiana Martínez and Marcos Fernández

Abstract: This paper describes a speech and text translator from Spanish into Spanish Sign Language, that tries to solve some of the problems that deaf people find when they access and attend specific training courses. In addition to the translator system, a set of real-time avatar animations representing the signs are used. The creation process of such avatars is also described. The system can be used in courses where deaf and hearing people are sharing the same material and classroom, which contributes to improve the integration of this group of people to specific academic areas. The tool has been tested to obtain direct information with a group of deaf people from the Deaf Association of Seville.

Paper Nr: 61
Title:

### Simulating and Validating Facial Expressions using an Anatomically Accurate Biomechanical Model Derived from MRI Data - Towards Fast and Realistic Generation of Animated Characters

Authors:

#### Tim Wu, Peter Hunter and Kumar Mithraratne

Abstract: A detailed high-order (cubic-Hermite) finite element model of the human head was constructed from anatomical data segmented from MR images. The model includes a superficial soft-tissue mesh (skin, subcutaneous layer and superficial musculo-aponeurotic system), 20 muscles of facial expressions and several deep structures. Based on the theory of finite deformation elasticity together with large deformation contact constraints, quasi-static facial expressions were generated by activating transversely isotropic muscles that were accurately depicted by their respective anatomical geometries. Material (muscle-fat) heterogeneity was also introduced to capture the realistic formation of skin folds. Using the described approach, four facial expressions were simulated and compared with the surface data obtained from a 3D structured-light scanner. Predicted expressions showed good agreement with the experimental data.

Posters
Paper Nr: 31
Title:

### On the Characterization of a Speed-boat Motion for Real-time Motion Cueing

Authors:

#### Sergio Casas, Inmaculada Coma, José V. Riera and Marcos Fernández

Abstract: Motion platforms are not uncommon for car and flight VR simulators. However, the same is not true about watercraft. This paper presents an experimental characterization of a speed-boat in order to understand the nature and magnitude of a typical small watercraft motion. Unlike other studies, this work focuses on real-time simulation instead of on boat design issues. The purpose of the study is to guide the future process of designing and parameterizing a suitable motion platform for a VR application. The characterization is performed by placing two accelerometers, two gyroscopes, one GPS logger, one digital compass, and one digital anemometer on a speed-boat at several ranges of motion and maneuvering. We analyze tilt, speed, wind, steering, angular speed, acceleration and angular acceleration at both frequency and time domains. Characterization results show that at least a 3-DoF heave-pitch-roll motion platform should be used.

## Area 4 - Interactive Environments

Full Papers
Paper Nr: 12
Title:

### Using a Graphics Turing Test to Evaluate the Effect of Frame Rate and Motion Blur on Telepresence of Animated Objects

Authors:

#### M. Borg, S. S. Johansen, K. S. Krog, D. L. Thomsen and M. Kraus

Abstract: A limited Graphics Turing Test is used to determine the frame rate that is required to achieve telepresence of an animated object. For low object velocities of 2.25 and 4.5 degrees of visual angle per second at 60 frames per second a rotating object with no added motion blur is able to pass the test. The results of the experiments confirm previous results in psychophysics and show that the Graphics Turing Test is a useful tool in computer graphics. Even with simulated motion blur, our Graphics Turing Test could not be passed with frame rates of 30 and 20 frames per second. Our results suggest that 60 frames per second (instead of 30 frames per second) should be considered the minimum frame rate to achieve object telepresence and that motion blur provides only limited benefits.

Paper Nr: 19
Title:

### Structuring Interactions in a Hybrid Virtual Environment - Infrastructure & Usability

Authors:

#### Pablo Almajano, Enric Mayas, Inmaculada Rodriguez, Maite Lopez-Sanchez and Anna Puig

Abstract: Humans in the Digital Age are continuously exploring different forms of socializing on-line. In Social 3D Virtual Worlds (VW) people freely socialize by participating in open-ended activities in 3D simulated spaces. Moreover, VWs can also be used to engage humans in e-applications, the so called Serious VWs. Implicitly, these serious applications have specific goals that require structured environments where participants play specific roles and perform activities by following well-defined protocols and norms. In this paper we advocate for the use of Virtual Institutions (VI) to provide explicit structure to current Social 3D VWs. We refer to the resulting system as hybrid (participants can be both human and software agents) and structured Virtual Environments. Specifically, we present v-mWater (a water market, an e-government application deployed as a VI), the infrastructure that supports participants’ interactions, and the evaluation of its usability.

Paper Nr: 26
Title:

### Photo-based Multimedia Applications using Image Features Detection

Authors:

#### Rui Nóbrega and Nuno Correia

Abstract: This paper proposes a framework for the creation of interactive multimedia applications that take advantage of detected features from user-captured photos. The goal is to create games, architectural and space planning applications that interact with visual elements in the images such as walls, floors and empty spaces. The framework takes advantage of a semi-automatic algorithm to detect scene elements and camera parameters. Using the detected features, virtual objects can be inserted in the scene. In this paper several example applications are presented and discussed, and the reliability of the detection algorithm is compared with other systems. The presented solution analyses the photos using graph-cuts for segmentation, vanishing point detection and line analysis to detect the scene elements. The main advantage of the proposed framework is the semi-automatic creation of the tri-dimensional model to be used in mixed reality applications. This enables scenarios where the user can be responsible for the input scene without much prior knowledge or experience. The current implemented examples include a furniture positioning system and a snake game with a user-built maze in the real world. The proposed system is ideal for multimedia mobile applications where interaction is combined with the back camera of the device.

Paper Nr: 48
Title:

### DAAPMed: A Data-aware Anchor Point Selection Tool for Medical Models in VR Environments

Authors:

#### Eva Monclús Lahoya, Pere-Pau Vázquez and Isabel Navazo Álvaro

Abstract: There is a number of problems where the analysis of medical datasets requires the selection of anchoring points in 3D space, such as the measurement of anatomical structures (i.e. lengths of bones), pathological structures (i.e. tumors), and the measurement of other elements such as the air contents in the lungs or the gut. Previous research indicates that measurement tasks can be usually carried out more efficiently in VR environments than in desktop-based systems. However, there is a lack of tools for measurement support for medical models in VR environments. This paper presents a new VR-based interaction technique, Data-Aware Anchor Points for Medical models (DAAPMed), specially focused on the efficient selection of 3D points in datasets rendered using methods with semi-transparency such as Direct Volume Rendering. We will show that our method is effective, precise, and reduces the amount of movements required to set the anchor points as compared with other classical techniques based on clipping planes.

Paper Nr: 52
Title:

### Optimization of an Autostereoscopic Display for a Driving Simulator

Authors:

#### Eva Eggeling, Dieter W. Fellner, Andreas Halm and Torsten Ullrich

Abstract: In this paper, we present an algorithm to optimize a 3D stereoscopic display based on parallax barriers for a driving simulator. The main purpose of the simulator is to enable user studies in reproducible laboratory conditions to test and evaluate driving assistance systems. The main idea of our optimization approach is to determine by numerical analysis the best pattern for an autostereoscopic display with the best image separation for each eye, integrated into a virtual reality environment. Our implementation uses a differential evolution algorithm, which is a parallel, direct search method based on evolution strategies, because it converges fast and is inherently parallel. This allows an execution on a network of computers. The resulting algorithm allows optimizing the display and its corresponding pattern, such that a single user in the simulator environment sees a stereoscopic image without being supported by special eye-wear.

Paper Nr: 54
Title:

### Guiding Techniques for Collaborative Exploration in Multi-scale Shared Virtual Environments

Authors:

#### Thi Thuong Huyen Nguyen, Thierry Duval and Cédric Fleury

Abstract: Exploration of large-scale 3D Virtual Environments (VEs) is often difficult because of lack of familiarity with complex virtual worlds, lack of spatial information that can be offered to users and lack of sensory (visual, auditory, locomotive) details compared to the exploration of real environments. To address this problem, we present a set of metaphors for assisting users in collaborative navigation to perform common exploration tasks in shared collaborative virtual environments. Our propositions consist in three guiding techniques in the form of navigation aids to enable one or several users (called helping user(s)) to help one main user (called exploring user) to explore the VE efficiently. These three techniques consist in drawing directional arrows, lighting up path to follow, and orienting a compass to show a direction to the exploring user. All the three techniques are generic so they can be used for any kind of 3D VE, and they do not affect the main structure of the VE so its integrity is guaranteed. To compare the efficiency of these three guiding techniques, we have conducted an experimental study of a collaborative task whose aim was to find hidden target objects in a complex and multi-scale shared 3D VE. Our results show that although the directional arrows and compass surpassed the light source for the navigation task, these three techniques are completely appropriate for guiding a user in 3D complex VEs.

Paper Nr: 62
Title:

### SODA: A Scalability-Oriented Distributed & Anticipative Model for Collision Detection in Physically-based Simulations

Authors:

#### Steve Dodier-Lazaro, Quentin Avril and Valérie Gouranton

Abstract: In this paper, we propose a distributed and anticipative model for collision detection and propose a lead for distributed collision handling, two key components of physically-based simulations of virtual environments. This model is designed to improve the scalability of interactive deterministic simulations on distributed systems such as PC clusters. Our main contribution consists of loosening synchronism constraints in the collision detection and response pipeline to allow the simulation to run in a decentralized, distributed fashion. To do so, we setup a spatial subdivision grid, and assign a subset of the simulation space to each processor, made of contiguous cells from this grid. These processors synchronize only with their direct neighbors in the grid, and only when an object moves from one’s area to another. We rely on the rarity of such synchronizations to allow anticipative computing that will also work towards improving scalability. When synchronizations occur, we propose an arrangement of collision checks and rollback algorithms that help reduce the processing cost of synchronized areas’ bodies. We show potential for distributed load balancing strategies based on the exchange of grid cells, and explain how anticipative computing may, in cases of short computational peaks, improve user experience by avoiding frame-rate drop-downs.

Short Papers
Paper Nr: 8
Title:

### 3D Interaction Assistance in Virtual Reality: A Semantic Reasoning Engine for Context-awareness - From Interests and Objectives Detection to Adaptations

Authors:

#### Yannick Dennemont, Guillaume Bouyer, Samir Otmane and Malik Mallem

Abstract: This work aims to provide 3D interaction assistance in virtual environments depending on context. We designed and implemented a generic decision engine that can connect to our existing virtual reality applications through a set of tools. It uses an ontology and Conceptual Graphs (CGs) to represent knowledge, and First Order Logic to conduct semantic reasoning. Context information are gathered by virtual sensors in the application and interpreted by the engine. Multimodal assistance is provided by virtual actuators. Our first test scenario is about assistance to selection of objects or navigation towards objects: the engine automatically detects user’s interests and manages adaptations depending on user’s hand gestures, interactions history and type of task.

Paper Nr: 10
Title:

### User Awareness for Collaborative Multi-touch Interaction

Authors:

#### Markus Schlattmann, Yuelong Yu, Nils Gruendl, Manfred Bogen, Alexander Kulik, David d'Angelo, Bernd Froehlich and Reinhard Klein

Abstract: Multi-touch enables direct manipulation of graphical computer interfaces. This intuitive interaction paradigm rapidly became popular, particularly in the domain of individual mobile devices. Collaborative work on large scale multi-touch devices, instead, suffers from mutual interferences if many simultaneous touch events cannot be attributed to individual users. On the example of a large, adjustable, high-resolution (4K) multi-touch device, we describe a lightweight and robust method to solve this issue. An additional depth camera above the tabletop device tracks the users around the table and their respective hands. This environment tracking and the multi-touch sensor are automatically calibrated to the same coordinate system. We discuss relevant implementation details to help practitioners building similar systems. Besides improved multi-user coordination we reveal general usability benefits including the reduction of false positives. Exploiting the developed system, we implemented several novel test applications to analyze the capabilities of such a system with regard to different interaction metaphors. Finally, we combined several of the analyzed metaphors to a novel application serving as an intuitive multi-touch application and environment for seismic interpretation.

Paper Nr: 75
Title:

### Improving Symbol Salience in Augmented Reality

Authors:

#### Maria Beatriz Carmo, Ana Paula Cláudio, António Ferreira, Ana Paula Afonso and Raúl Simplício

Abstract: In augmented reality applications, users may experience difficulty in finding virtual symbols placed over images of the real world whenever the colour of the surrounding background becomes similar to the symbols’ colour. We investigated a set of adaptations to make virtual symbols more salient from the background, while maintaining the original semantics, and conducted a study to evaluate user preferences about the adaptations, which revealed that adding a border to the symbols was favoured by the majority of the participants. Next came colour luminosity adjustment and changing the colour of the letters inside the symbol; however the latter was only preferred against symbols with no adaptation, that is, it was never chosen when competing with the other adaptations. Enlarging the symbol was the least selected adaptation, followed by having no adaptation at all. These results suggest using adaptations based on border addition and colour luminosity adjustments in the representation of virtual symbols for augmented reality.

Paper Nr: 80
Title:

### The Perceptive Puppet - Seamless Embodiment Exchange between Real and Virtual Humans in Virtual Environments for Training

Authors:

#### Andrés Saraos Luna, Valérie Gouranton, Thomas Lopez and Bruno Arnaldi

Abstract: We present a novel mechanism that allows real and virtual humans to dynamically exchange the control of their embodiment in virtual environments. Such a mechanism raises two important issues: the possibility of dynamic embodiment exchanges between real humans and virtual humans and the continuity of actions of the team members after an exchange. To address these issues we introduce a new entity, the Perceptive Puppet that abstracts real and virtual humans into one common entity containing its own knowledge.

Posters
Paper Nr: 6
Title:

### On the Implementation of Servers for Large Scale CAR Systems based on Mobile Phones

Authors:

#### Víctor Fernández, Juan Manuel Orduña and Pedro Morillo

Abstract: This paper presents the experimental comparison of different server implementations for CAR systems based on mobile phones. The results show that the UDP-based implementation provides a significant improvement in system throughput, supporting more than one thousand client devices at interactive rates, at the cost of loosing a very small percentage of updating messages.

Paper Nr: 17
Title:

### Transfer of Juggling Skills Acquired in a Virtual Environment

Authors:

#### A. P. Hauge, C. S. Kragegaard, E. B. Kjæhr and M. Kraus

Abstract: This paper explores whether motoric skills acquired within a virtual training environment can be successfully transferred to the real world by comparing a virtual environment with a traditional learning environment. Specifically, a system for learning juggling with virtual balls was designed with a focus on approximating natural interaction. We propose a method of evaluating the acquisition and transfer of motoric skills through a virtual environment, which is compared to a traditional learning environment. Each environment was evaluated using various criteria ranging from improvement in skills to observations of performance. The findings suggest that a transfer of motoric skills and knowledge takes place for users of the virtual system with only little difference between the environments. They also suggest that a virtual environment can create a less frustrating learning experience.

Paper Nr: 23
Title:

### Comparing Touch and Tilt Interaction using an iPhone Game for Children

Authors:

#### David Furió, M.-Carmen Juan, Ignacio Seguí, M. José Vicent and Francisco Abad

Abstract: In this paper, we present a study that compares tilt and touch-screen interaction in a 2D iPhone game for children. The trials involved 58 children from 8 to 10 years old. The results showed that the children found touch-screen interaction easier. With regard to engagement and fun, no significant differences were found between the two interaction methods. However, differences between boys and girls were found with the score given to the game. Another interesting result is that the children had no preferred interaction method.

Paper Nr: 39
Title:

### Tactile and Tangible Interfaces in Handheld AR for Children

Authors:

#### Santiago González-Gancedo, M.-Carmen Juan, Ignacio Seguí and Francisco Abad

Abstract: This paper presents a comparative study between tangible user interfaces (TUIs) and tactile user interfaces (TacUIs) in handheld AR, with a contribution to the state of the art in HCI oriented to children. While TUIs work with the manipulation of physical objects, TacUIs work with virtual representations of them. In our evaluations to compare these two interactions with primary school children, we found that the TacUI was the fastest for completing the task, what makes it better suited for educational purposes. The TacUI was found easier to use by the children, although the TUI was found more solid and less slippery. Our conclusions should be of interest not only to educational researchers, but also to the general HCI community working on tangible and tactile interfaces.

Paper Nr: 43
Title:

### GPU-accelerated Real-time Markerless Human Motion Capture

Authors:

#### Christian Rau and Guido Brunnett

Abstract: We present a system for capturing human motions based on video data from multiple cameras. It realizes a 3-dimensional voxel-based reconstruction of the human together with an estimation of the pose of his complete body in each frame. The use of an underlying kinematic skeleton together with an idealized geometric model can guarantee a valid pose even in the face of occlusions caused by the incomplete spatial information gained from the cameras. The data-parallel nature of the used algorithms makes them well-suited for the implementation on modern graphics hardware. In this way the motion can be captured in real-time on a single PC despite the computation of a reconstruction accurate enough for a high quality pose estimation.

## Area 5 - Social Agents in Computer Graphics

Full Papers
Paper Nr: 21
Title:

### Generating Co-occurring Facial Nonmanual Signals in Synthesized American Sign Language

Authors:

#### Jerry Schnepp, Rosalee Wolfe, John McDonald and Jorge Toro

Abstract: Translating between English and American Sign Language (ASL) requires an avatar to display synthesized ASL. Essential to the language are nonmanual signals that appear on the face. In the past, these have posed a difficult challenge for signing avatars. Previous systems were hampered by an inability to portray simultaneously-occurring nonmanual signals on the face. This paper presents a method designed for supporting co-occurring nonmanual signals in ASL. Animations produced by the new system were tested with 40 members of the Deaf community in the United States. Participants identified all of the nonmanual signals even when they co-occurred. Co-occurring question nonmanuals and affect information were distinguishable, which is particularly promising because the two processes move an avatar’s brows in a competing manner. This brings the state of the art one step closer to the goal of an automatic English-to-ASL translator.

Paper Nr: 21
Title:

### Generating Co-occurring Facial Nonmanual Signals in Synthesized American Sign Language

Authors:

#### Jerry Schnepp, Rosalee Wolfe, John McDonald and Jorge Toro

Abstract: Translating between English and American Sign Language (ASL) requires an avatar to display synthesized ASL. Essential to the language are nonmanual signals that appear on the face. In the past, these have posed a difficult challenge for signing avatars. Previous systems were hampered by an inability to portray simultaneously-occurring nonmanual signals on the face. This paper presents a method designed for supporting co-occurring nonmanual signals in ASL. Animations produced by the new system were tested with 40 members of the Deaf community in the United States. Participants identified all of the nonmanual signals even when they co-occurred. Co-occurring question nonmanuals and affect information were distinguishable, which is particularly promising because the two processes move an avatar’s brows in a competing manner. This brings the state of the art one step closer to the goal of an automatic English-to-ASL translator.

Posters
Paper Nr: 63
Title:

### Affect Recognition during Active Game Playing based on Posture Skeleton Data

Authors:

#### Haris Zacharatos, Christos Gatzoulis and Yiorgos Chrysanthou

Abstract: The affective state of a player during game playing has a significant effect on the player’s motivation and engagement. Recognising player’s emotions during games can help game designers improve the user experience by providing sophisticated behaviours to the game characters and the system itself. This paper presents work-in-progress towards novel recognition of player’s emotions using posture skeleton data as input from non-intrusive interfaces. A database of samples of non-acted posture skeleton data was captured during active game playing using Microsoft Kinect’s sensors. Four observers were asked to annotate the selected postures with an emotion label from a given emotion set. Based on Cohen’s kappa, the agreement level of the observers was above or equal to ‘good’ with overall agreement levels that outperform existing benchmarks. The data was used in a series of experiments for training the system in recognising emotions. The results indicate that the compiled database of postures annotated with emotion labels performs considerably above chance level recognition of emotions and offers interesting research questions for improvements and future directions in the area.