Volume 28 (2009)

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https://diglib.eg.org/handle/10.2312/142

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Structure-Preserving Reshape for Textured Architectural Scenes
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Cabral, Marcio; Lefebvre, Sylvain; Dachsbacher, Carsten; Drettakis, George
Modeling large architectural environments is a difficult task due to the intricate nature of these models and the complex dependencies between the structures represented. Moreover, textures are an essential part of architectural models. While the number of geometric primitives is usually relatively low (i.e., many walls are at surfaces), textures actually contain many detailed architectural elements.We present an approach for modeling architectural scenes by reshaping and combining existing textured models, where the manipulation of the geometry and texture are tightly coupled. For geometry, preserving angles such as oor orientation or vertical walls is of key importance. We thus allow the user to interactively modify lengths of edges, while constraining angles. Our texture reshaping solution introduces a measure of directional autosimilarity to focus stretching in areas of stochastic content and to preserve details in such areas.We show results on several challenging models, and show two applications: Building complex road structures from simple initial pieces and creating complex game-levels from an existing game based on pre-existing model pieces.
Tactics-Based Behavioural Planning for Goal-Driven Rigid Body Control
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Zickler, Stefan; Veloso, Manuela
Controlling rigid body dynamic simulations can pose a difficult challenge when constraints exist on the bodies goal states and the sequence of intermediate states in the resulting animation. Manually adjusting individual rigid body control actions (forces and torques) can become a very labour-intensive and non-trivial task, especially if the domain includes a large number of bodies or if it requires complicated chains of inter-body collisions to achieve the desired goal state. Furthermore, there are some interactive applications that rely on rigid body models where no control guidance by a human animator can be offered at runtime, such as video games.In this work, we present techniques to automatically generate intelligent control actions for rigid body simulations. We introduce sampling-based motion planning methods that allow us to model goal-driven behaviour through the use of non-deterministic Tactics that consist of intelligent, sampling-based control-blocks, called Skills. We introduce and compare two variations of a Tactics-driven planning algorithm, namely behavioural Kinodynamic Rapidly Exploring Random Trees (BK-RRT) and Behavioural Kinodynamic Balanced Growth Trees (BK-BGT). We show how our planner can be applied to automatically compute the control sequences for challenging physics-based domains and that is scalable to solve control problems involving several hundred interacting bodies, each carrying unique goal constraints.
Structure from silhouettes: a new paradigm for fast sketch-based design of trees
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Wither, J.; Boudon, F.; Cani, M.-P.; Godin, C.
Modeling natural elements such as trees in a plausible way, while offering simple and rapid user control, is a challenge. This paper presents a method based on a new structure from silhouettes paradigm. We claim that sketching the silhouettes of foliage at multiple scales is quicker and more intuitive for a user than having to sketch each branch of a tree. This choice allows us to incorporate botanical knowledge, enabling us to infer branches that connect in a plausible way to their parent branch and have a correct distribution in 3D. We illustrate these ideas by presenting a seamless sketch-based interface, used for sketching foliage silhouettes from the scale of an entire tree to the scale of a leaf. Each sketch serves for inferring both the branches at that level and construction lines to serve as support for sub-silhouette refinement. When the user finally zooms out, the style inferred for the branching systems he has refined (in terms of branch density, angle, length distribution and shape) is duplicated to the unspecified branching systems at the same level. Meanwhile, knowledge from botany is again used for extending the branch distribution to 3D, resulting in a full, plausible 3D tree that fits the user-sketched contours. As our results show, this system can be of interest to both experts and novice users. While experts can fully specify all parts of a tree and over-sketch specific branches if required, any user can design a basic 3D tree in one or two minutes, as easily as sketching it with paper and pen.
Simulation of two-phase flow with sub-scale droplet and bubble effects
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Mihalef, Viorel; Metaxas, Dimitris; Sussman, Mark
We present a new Eulerian-Lagrangian method for physics-based simulation of fluid flow, which includes automatic generation of sub-scale spray and bubbles. The Marker Level Set method is used to provide a simple geometric criterion for free marker generation. A filtering method, inspired from Weber number thresholding, further controls the free marker generation (in a physics-based manner). Two separate models are used, one for sub-scale droplets, the other for sub-scale bubbles. Droplets are evolved in a Newtonian manner, using a density-extension drag force field, while bubbles are evolved using a model based on Stokes Law. We show that our model for sub-scale droplet and bubble dynamics is simple to couple with a full (macro-scale) Navier-Stokes two-phase flow model and is quite powerful in its applications. Our animations include coarse grained multiphase features interacting with fine scale multiphase features.
Bivariate Transfer Functions on Unstructured Grids
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Song, Yuyan; Chen, Wei; Maciejewski, Ross; Gaither, Kelly P.; Ebert, David S.; H.-C. Hege, I. Hotz, and T. Munzner
Multi-dimensional transfer functions are commonly used in rectilinear volume renderings to effectively portray materials, material boundaries and even subtle variations along boundaries. However, most unstructured grid rendering algorithms only employ one-dimensional transfer functions. This paper proposes a novel pre-integrated Projected Tetrahedra (PT) rendering technique that applies bivariate transfer functions on unstructured grids. For each type of bivariate transfer function, an analytical form that pre-integrates the contribution of a ray segment in one tetrahedron is derived, and can be precomputed as a lookup table to compute the color and opacity in a projected tetrahedron on-the-fly. Further, we show how to approximate the integral using the pre-integration method for faster unstructured grid rendering. We demonstrate the advantages of our approach with a variety of examples and comparisons with one-dimensional transfer functions.
Fast GPU-based Adaptive Tessellation with CUDA
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Schwarz, Michael; Stamminger, Marc
Compact surface descriptions like higher-order surfaces are popular representations for both modeling and animation. However, for fast graphics-hardware-assisted rendering, they usually need to be converted to triangle meshes. In this paper, we introduce a new framework for performing on-the-fly crack-free adaptive tessellation of surface primitives completely on the GPU. Utilizing CUDA and its flexible memory write capabilities, we parallelize the tessellation task at the level of single surface primitives. We are hence able to derive tessellation factors, perform surface evaluation as well as generate the tessellation topology in real-time even for large collections of primitives. We demonstrate the power of our framework by exemplarily applying it to both bicubic rational Bezier patches and PN triangles.
SecondSkin: An interactive method for appearance transfer
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Van Den Hengely, A.; Sale, D.; Dick, A. R.
SecondSkin estimates an appearance model for an object visible in a video sequence, without the need for complex interaction or any calibration apparatus. This model can then be transferred to other objects, allowing a non-expert user to insert a synthetic object into a real video sequence so that its appearance matches that of an existing object, and changes appropriately throughout the sequence. As the method does not require any prior knowledge about the scene, the lighting conditions, or the camera, it is applicable to video which was not captured with this purpose in mind. However, this lack of prior knowledge precludes the recovery of separate lighting and surface reflectance information. The SecondSkin appearance model therefore combines these factors. The appearance model does require a dominant light-source direction, which we estimate via a novel process involving a small amount of user interaction. The resulting model estimate provides exactly the information required to transfer the appearance of the original object to new geometry composited into the same video sequence.
Shape Decomposition using Modal Analysis
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Huang, Qi-Xing; Wicke, Martin; Adams, Bart; Guibas, Leonidas
We introduce a novel algorithm that decomposes a deformable shape into meaningful parts requiring only a single input pose. Using modal analysis, we are able to identify parts of the shape that tend to move rigidly. We define a deformation energy on the shape, enabling modal analysis to find the typical deformations of the shape. We then find a decomposition of the shape such that the typical deformations can be well approximated with deformation fields that are rigid in each part of the decomposition. We optimize for the best decomposition, which captures how the shape deforms. A hierarchical refinement scheme makes it possible to compute more detailed decompositions for some parts of the shape.Although our algorithm does not require user intervention, it is possible to control the process by directly changing the deformation energy, or interactively refining the decomposition as necessary. Due to the construction of the energy function and the properties of modal analysis, the computed decompositions are robust to changes in pose as well as meshing, noise, and even imperfections such as small holes in the surface.
Optimizing Structure Preserving Embedded Deformation for Resizing Images and Vector Art
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Huang, Qi-xing; Mech, Radomir; Carr, Nathan
Smart deformation and warping tools play an important part in modern day geometric modeling systems. They allow existing content to be stretched or scaled while preserving visually salient information. To date, these techniques have primarily focused on preserving local shape details, not taking into account important global structures such as symmetry and line features. In this work we present a novel framework that can be used to preserve the global structure in images and vector art. Such structures include symmetries and the spatial relations in shapes and line features in an image. Central to our method is a new formulation of preserving structure as an optimization problem. We use novel optimization strategies to achieve the interactive performance required by modern day modeling applications. We demonstrate the effectiveness of our framework by performing structure preservation deformation of images and complex vector art at interactive rates.
Table of Contents and Cover
(The Eurographics Association and Blackwell Publishing Ltd, 2009)
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Interior Distance Using Barycentric Coordinates
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Rustamov, R. M.; Lipman, Y.; Funkhouser, T.
This paper introduces a framework for defining a shape-aware distance measure between any two points in the interior of a surface mesh. Our framework is based on embedding the surface mesh into a high-dimensional space in a way that best preserves boundary distances between vertices of the mesh, performing a mapping of the mesh volume into this high-dimensional space using barycentric coordinates, and defining the interior distance between any two points simply as their Euclidean distance in the embedding space. We investigate the theoretical properties of the interior distance in relation to properties of the chosen boundary distances and barycentric coordinates, and we investigate empirical properties of the interior distance using diffusion distance as the prescribed boundary distance and mean value coordinates. We prove theoretically that the interior distance is a metric, smooth, interpolating the boundary distances, and reproducing Euclidean distances, and we show empirically that it is insensitive to boundary noise and deformation and quick to compute. In case the barycentric coordinates are non-negative we also show a maximum principle exists. Finally, we use it to define a new geometric property, barycentroid of shape, and show that it captures the notion of semantic center of the shape.
Hierarchical Image-Space Radiosity for Interactive Global Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Nichols, Greg; Shopf, Jeremy; Wyman, Chris
We introduce image-space radiosity and a hierarchical variant as a method for interactively approximating diffuse indirect illumination in fully dynamic scenes. As oft observed, diffuse indirect illumination contains mainly low-frequency details that do not require independent computations at every pixel. Prior work leverages this to reduce computation costs by clustering and caching samples in world or object space. This often involves scene preprocessing, complex data structures for caching, or wasted computations outside the view frustum. We instead propose clustering computations in image space, allowing the use of cheap hardware mipmapping and implicit quadtrees to allow coarser illumination computations. We build on a recently introduced multiresolution splatting technique combined with an image-space lightcut algorithm to intelligently choose virtual point lights for an interactive, one-bounce instant radiosity solution. Intelligently selecting point lights from our reflective shadow map enables temporally coherent illumination similar to results using more than 4096 regularly-sampled VPLs.
Interactive Rendering of Interior Scenes with Dynamic Environment Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Yue, Yonghao; Iwasaki, Kei; Chen, Bing-Yu; Dobashi, Yoshinori; Nishita, Tomoyuki
A rendering system for interior scenes is proposed in this paper. The light reaches the interior scene, usually through small regions, such as windows or abat-jours, which we call portals. To provide a solution, suitable for rendering interior scenes with portals, we extend the traditional precomputed radiance transfer approaches. In our approach, a bounding sphere, which we call a shell, of the interior, centered at each portal, is created and the light transferred from the shell towards the interior through the portal is precomputed. Each shell acts as an environment light source and its intensity distribution is determined by rendering images of the scene, viewed from the center of the shell. By updating the intensity distribution of the shell at each frame, we are able to handle dynamic objects outside the shells. The material of the portals can also be modified at run time (e.g. changing from transparent glass to frosted glass). Several applications are shown, including the illumination of a cathedral, lit by skylight at different times of a day, and a car, running in a town, at interactive frame rates, with a dynamic viewpoint.
Symmetry Detection Using Feature Lines
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Bokeloh, M.; Berner, A.; Wand, M.; Seidel, H.-P.; Schilling, A.
In this paper, we describe a new algorithm for detecting structural redundancy in geometric data sets. Our algorithm computes rigid symmetries, i.e., subsets of a surface model that reoccur several times within the model differing only by translation, rotation or mirroring. Our algorithm is based on matching locally coherent constellations of feature lines on the object surfaces. In comparison to previous work, the new algorithm is able to detect a large number of symmetric parts without restrictions to regular patterns or nested hierarchies. In addition, working on relevant features only leads to a strong reduction in memory and processing costs such that very large data sets can be handled. We apply the algorithm to a number of real world 3D scanner data sets, demonstrating high recognition rates for general patterns of symmetry.
Semi-Supervised Learning in Reconstructed Manifold Space for 3D Caricature Generation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Liu, Junfa; Chen, Yiqiang; Miao, Chunyan; Xie, Jinjing; Ling, Charles X.; Gao, Xingyu; Gao, Wen
Recently, automatic 3D caricature generation has attracted much attention from both the research community and the game industry. Machine learning has been proven effective in the automatic generation of caricatures. However, the lack of 3D caricature samples makes it challenging to train a good model. This paper addresses this problem by two steps. First, the training set is enlarged by reconstructing 3D caricatures. We reconstruct 3D caricatures based on some 2D caricature samples with a Principal Component Analysis (PCA)-based method. Secondly, between the 2D real faces and the enlarged 3D caricatures, a regressive model is learnt by the semi-supervised manifold regularization (MR) method. We then predict 3D caricatures for 2D real faces with the learnt model. The experiments show that our novel approach synthesizes the 3D caricature more effectively than traditional methods. Moreover, our system has been applied successfully in a massive multi-user educational game to provide human-like avatars.
Frontmatter
(The Eurographics Association and Blackwell Publishing Ltd, 2009)
Motion Compression using Principal Geodesics Analysis
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Tournier, M.; Wu, X.; Courty, N.; Arnaud, E.; Reveret, L.
Due to the growing need for large quantities of human animation data in the entertainment industry, it has become a necessity to compress motion capture sequences in order to ease their storage and transmission. We present a novel, lossy compression method for human motion data that exploits both temporal and spatial coherence. Given one motion, we first approximate the poses manifold using Principal Geodesics Analysis (PGA) in the configuration space of the skeleton. We then search this approximate manifold for poses matching end-effectors constraints using an iterative minimization algorithm that allows for real-time, data-driven inverse kinematics. The compression is achieved by only storing the approximate manifold parametrization along with the end-effectors and root joint trajectories, also compressed, in the output data. We recover poses using the IK algorithm given the end-effectors trajectories. Our experimental results show that considerable compression rates can be obtained using our method, with few reconstruction and perceptual errors.
Texture Splicing
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Liu, Yiming; Wang, Jiaping; Xue, Su; Tong, Xin; Kang, Sing Bing; Guo, Baining
We propose a new texture editing operation called texture splicing. For this operation, we regard a texture as having repetitive elements (textons) seamlessly distributed in a particular pattern. Taking two textures as input, texture splicing generates a new texture by selecting the texton appearance from one texture and distribution from the other. Texture splicing involves self-similarity search to extract the distribution, distribution warping, context-dependent warping, and finally, texture refinement to preserve overall appearance. We show a variety of results to illustrate this operation.
Range Scan Registration Using Reduced Deformable Models
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Chang, W.; Zwicker, M.
We present an unsupervised method for registering range scans of deforming, articulated shapes. The key idea is to model the motion of the underlying object using a reduced deformable model. We use a linear skinning model for its simplicity and represent the weight functions on a regular grid localized to the surface geometry. This decouples the deformation model from the surface representation and allows us to deal with the severe occlusion and missing data that is inherent in range scan data. We formulate the registration problem using an objective function that enforces close alignment of the 3D data and includes an intuitive notion of joints. This leads to an optimization problem that we solve using an efficient EM-type algorithm. With our algorithm we obtain smooth deformations that accurately register pairs of range scans with significant motion and occlusion. The main advantages of our approach are that it does not require user specified markers, a template, nor manual segmentation of the surface geometry into rigid parts.
Selecting Good Views of High-dimensional Data using Class Consistency
(The Eurographics Association and Blackwell Publishing Ltd., 2009) Sips, Mike; Neubert, Boris; Lewis, John P.; Hanrahan, Pat; H.-C. Hege, I. Hotz, and T. Munzner
Abstract Many visualization techniques involve mapping high-dimensional data spaces to lower-dimensional views. Unfortunately, mapping a high-dimensional data space into a scatterplot involves a loss of information; or, even worse, it can give a misleading picture of valuable structure in higher dimensions. In this paper, we propose class consistency as a measure of the quality of the mapping. Class consistency enforces the constraint that classes of n D data are shown clearly in 2 D scatterplots. We propose two quantitative measures of class consistency, one based on the distance to the class s center of gravity, and another based on the entropies of the spatial distributions of classes. We performed an experiment where users choose good views, and show that class consistency has good precision and recall. We also evaluate both consistency measures over a range of data sets and show that these measures are efficient and robust.

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