Computer Graphics Forum

Cover image for Vol. 32 Issue 1

February 2013

Volume 32, Issue 1

Pages i–ii, 1–219

  1. Issue Information

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Reports
    6. Erratum
    1. Issue Information (pages i–ii)

      Version of Record online: 21 FEB 2013 | DOI: 10.1111/cgf.12011

  2. Editorial

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Reports
    6. Erratum
    1. Editorial (pages 1–2)

      Holly Rushmeier and Oliver Deussen

      Version of Record online: 21 FEB 2013 | DOI: 10.1111/cgf.12016

  3. Articles

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Reports
    6. Erratum
    1. Scalable Symmetry Detection for Urban Scenes (pages 3–15)

      J. Kerber, M. Bokeloh, M. Wand and H.-P. Seidel

      Version of Record online: 9 OCT 2012 | DOI: 10.1111/j.1467-8659.2012.03226.x

      Thumbnail image of graphical abstract

      In this paper we present a novel method for detecting partial symmetries in very large point clouds of 3D city scans. Unlike previous work, which has only been demonstrated on data sets of a few hundred megabytes maximum, our method scales to very large scenes: We map the detection problem to a nearest-neighbor problem in a lowdimensional feature space, and follow this with a cascade of tests for geometric clustering of potential matches. Our algorithm robustly handles noisy real-world scanner data, obtaining a recognition performance comparable to that of state-of-the-art methods. In practice, it scales linearly with scene size and achieves a high absolute throughput, processing half a terabyte of scanner data overnight on a dual socket commodity PC.

    2. Efficient GPU Data Structures and Methods to Solve Sparse Linear Systems in Dynamics Applications (pages 16–26)

      Daniel Weber, Jan Bender, Markus Schnoes, André Stork and Dieter Fellner

      Version of Record online: 12 OCT 2012 | DOI: 10.1111/j.1467-8659.2012.03227.x

      Thumbnail image of graphical abstract

      We present GPU data structures and algorithms to efficiently solve sparse linear systems which are typically required in simulations of multibody systems and deformable bodies. Thereby, we introduce an efficient sparse matrix data structure that can handle arbitrary sparsity patterns and outperforms current state-of-the-art implementations for sparse matrix vector multiplication. Moreover, an efficient method to construct global matrices on the GPU is presented where hundreds of thousands of individual element contributions are assembled in a few milliseconds. A finite element based method for the simulation of deformable solids as well as an impulse-based method for rigid bodies are introduced in order to demonstrate the advantages of the novel data structures and algorithms. These applications share the characteristic that a major computational effort consists of building and solving systems of linear equations in every time step. Our solving method results in a speed-up factor of up to 13 in comparison to other GPU methods.

    3. Synthetic Controllable Turbulence Using Robust Second Vorticity Confinement (pages 27–35)

      S He and R. W. H. Lau

      Version of Record online: 4 OCT 2012 | DOI: 10.1111/j.1467-8659.2012.03228.x

      Thumbnail image of graphical abstract

      Capturing fine details of turbulence on a coarse grid is one of the main tasks in real-time fluid simulation. Existing methods for doing this have various limitations. In this paper, we propose a new turbulence method that uses a refined Second Vorticity Confinement method, referred to as Robust Second Vorticity Confinement, and a synthesis scheme to create highly turbulent effects from coarse grid. The new technique is sufficiently stable to efficiently produce highly turbulent flows, while allowing intuitive control of vortical structures. Second Vorticity Confinement captures and defines the vortical features of turbulence on a coarse grid. However, due to the stability problem, it cannot be used to produce highly turbulent flows. In this work, we propose a robust formulation to improve the stability problem by making the positive diffusion term to vary with helicity adaptively. In addition, we also employ our new method to procedurally synthesize the high resolution flow fields. As shown in our results, this approach produces stable high resolution turbulence very efficiently.

    4. Vega: Non-Linear FEM Deformable Object Simulator (pages 36–48)

      F. S. Sin, D. Schroeder and J. Barbič

      Version of Record online: 23 NOV 2012 | DOI: 10.1111/j.1467-8659.2012.03230.x

      Thumbnail image of graphical abstract

      This practice and experience paper describes a robust C++ implementation of several nonlinear solid 3D deformable object strategies commonly employed in computer graphics, named the Vega FEM simulation library. Deformable models supported include co-rotational linear FEM elasticity, Saint-Venant Kirchhoff FEM model, mass-spring system, and invertible FEM models: neo-Hookean, Saint-Venant Kirchhoff, and Mooney-Rivlin. We provide several timestepping schemes, including implicit Newmark and backward Euler integrators, and explicit central differences. The implementation of material models is separated from integration, which makes it possible to employ our code not only for simulation, but also for deformable object control and shape modeling. We extensively compare the different material models and timestepping schemes. We provide practical experience and insight gained while using our code in several computer animation and simulation research projects.

    5. Visualization and Analysis of Second-Order Tensors: Moving Beyond the Symmetric Positive-Definite Case (pages 49–74)

      A. Kratz, C. Auer, M. Stommel and I. Hotz

      Version of Record online: 19 NOV 2012 | DOI: 10.1111/j.1467-8659.2012.03231.x

      Thumbnail image of graphical abstract

      Tensors provide a powerful language to describe physical phenomena. In this review, we focus on second-order tensors that are not diffusionensors. Until now, these tensors, which might be neither positive-definite nor symmetric, are underrepresented in visualization and existing visualization tools are often not appropriate for these tensors. Hence, we discuss the strengths and limitations of existing methods when dealing with such tensors as well as challenges introduced by them. The goal of this paper is to reveal the importance of the field and to encourage the development of new visualization methods for tensors from various application fields.

    6. Large and Small Eddies Matter: Animating Trees in Wind Using Coarse Fluid Simulation and Synthetic Turbulence (pages 75–84)

      A. Selino and M. D. Jones

      Version of Record online: 6 DEC 2012 | DOI: 10.1111/j.1467-8659.2012.03232.x

      Thumbnail image of graphical abstract

      Prior work on two-way coupling between fluid and deformable models lacks a subgrid resolution turbulence model. We produce realistic animations of tree motion by including motion due to both large and small eddies using synthetic subgrid turbulence and porous proxy geometry. Synthetic turbulence at the subgrid scale is modulated using turbulent kinetic energy (TKE). Adding noise after sampling the mean flow and TKE transfers energy from small eddies directly to the tree geometry. The resulting animations include both global sheltering effects and small scale leaf and branch motion. Viewers, on average, found animations which included both coarse fluid simulation and TKE-modulated noise to be more accurate than animations generated using coarse fluid simulation or noise alone.

    7. Fast Insertion-Based Optimization of Bounding Volume Hierarchies (pages 85–100)

      Jiří Bittner, Michal Hapala and Vlastimil Havran

      Version of Record online: 22 JAN 2013 | DOI: 10.1111/cgf.12000

      Thumbnail image of graphical abstract

      We present an algorithm for fast optimization of bounding volume hierarchies (BVH) for efficient ray tracing. We perform selective updates of the hierarchy driven by the cost model derived from the surface area heuristic. In each step the algorithm updates a fraction of the hierarchy nodes in order to minimize the overall hierarchy cost. The updates are realized by simple operations on the tree nodes: removal, search, and insertion. Our method can quickly reduce the cost of the hierarchy constructed by the traditional techniques such as the surface area heuristic. We evaluate the properties of the proposed method on fourteen test scenes of different complexity including individual objects and architectural scenes. The results show that our method can improve a BVH initially constructed with the surface area heuristic by up to 27% and a BVH constructed with the spatial median split by up to 88%.

    8. Perceptual Metrics for Static and Dynamic Triangle Meshes (pages 101–125)

      M. Corsini, M. C. Larabi, G. Lavoué, O. Petřík, L. Váša and K. Wang

      Version of Record online: 15 JAN 2013 | DOI: 10.1111/cgf.12001

      Thumbnail image of graphical abstract

      In this review, we discuss the existing comparison metrics for static and dynamic (animated) triangle meshes. We describe the concepts used in perception-oriented metrics used for 2D image comparison, and we show how these concepts are employed in existing 3D mesh metrics. We describe the character of subjective data used for evaluation of mesh metrics and provide comparison results identifying the advantages and drawbacks of each method. Finally, we also discuss employing the perception-correlated metrics in perception-oriented mesh processing algorithms.

      Corrected by:

      Erratum: Erratum

      Vol. 32, Issue 6, 251, Version of Record online: 18 MAY 2013

    9. Just-in-Time Texture Synthesis (pages 126–138)

      Lili Wang, Yulong Shi, Yi Chen and Voicu Popescu

      Version of Record online: 6 DEC 2012 | DOI: 10.1111/cgf.12003

      Thumbnail image of graphical abstract

      We present a just-intime texturing method that addresses these two problems. Texture diversification is achieved by modeling a texture patch as an umbrella, a versatile hybrid 3-D geometry and texture structure with parameterized appearance. The LoD is adapted continuously with a hierarchical algorithm that acts directly on the arrangement map. Results show that our method can model and render the diversity present in nature with only small texture memory requirements.

    10. Robust Image Denoising Using a Virtual Flash Image for Monte Carlo Ray Tracing (pages 139–151)

      Bochang Moon, Jong Yun Jun, JongHyeob Lee, Kunho Kim, Toshiya Hachisuka and Sung-Eui Yoon

      Version of Record online: 11 JAN 2013 | DOI: 10.1111/cgf.12004

      Thumbnail image of graphical abstract

      We propose an efficient and robust image-space denoising method for noisy images generated by Monte Carlo ray tracing methods. Our method is based on two new concepts: virtual flash images and homogeneous pixels. Inspired by recent developments in flash photography, virtual flash images emulate photographs taken with a flash, to capture various features of rendered images without taking additional samples. Using a virtual flash image as an edge-stopping function, our method can preserve image features that were not captured well only by existing edge-stopping functions such as normals and depth values.

    11. Interactive Planarization and Optimization of 3D Meshes (pages 152–163)

      Roi Poranne, Elena Ovreiu and Craig Gotsman

      Version of Record online: 21 FEB 2013 | DOI: 10.1111/cgf.12005

      Thumbnail image of graphical abstract

      Constraining 3D meshes to restricted classes is necessary in architectural and industrial design, but it can be very challenging to manipulate meshes while staying within these classes. Specifically, polyhedral meshes - those having planar faces - are very important, but also notoriously difficult to generate and manipulate efficiently. We describe an interactive method for computing, optimizing and editing polyhedral meshes. Efficiency is achieved thanks to a numerical procedure combining an alternating least-squares approach with the penalty method. This approach is generalized to manipulate other subsets of polyhedral meshes, as defined by a variety of other constraints.

    12. Feature-Preserving Surface Reconstruction From Unoriented, Noisy Point Data (pages 164–176)

      J. Wang, Z. Yu, W. Zhu and J. Cao

      Version of Record online: 11 JAN 2013 | DOI: 10.1111/cgf.12006

      Thumbnail image of graphical abstract

      We propose a robust method for surface mesh reconstruction from unorganized, unoriented, noisy and outlierridden 3D point data. A kernel-based scale estimator is introduced to estimate the scale of inliers of the input data. The best tangent planes are computed for all points based on mean shift clustering and adaptive scale sample consensus, followed by detecting and removing outliers. We estimate the normals for the remaining points and smooth the noise using a surface fitting and projection strategy. We then adopt an existing method to reconstruct surface meshes from the processed point data. We then describe a two-step approach to effectively recover original sharp features.

    13. Coarse-to-Fine Isometric Shape Correspondence by Tracking Symmetric Flips (pages 177–189)

      Y. Sahillioğlu and Y. Yemez

      Version of Record online: 11 JAN 2013 | DOI: 10.1111/cgf.12007

      Thumbnail image of graphical abstract

      We address the symmetric flip problem that is inherent to multiresolution isometric shape matching algorithms.To this effect, we extend our previous work which handles the dense isometric correspondence problem in the original 3D Euclidean space via coarse-to-fine combinatorial matching. The key idea is based on keeping track of all optimal solutions, which may be more than one due to symmetry especially at coarse levels, throughout denser levels of the shape matching process. We compare the resulting dense correspondence algorithm with state-of-the-art techniques over several 3D shape benchmark datasets. The experiments show that our method, which is fast and scalable, is performance-wise better than or on a par with the best performant algorithms existing in the literature for isometric (or nearly isometric) shape correspondence.

    14. Content-Based Colour Transfer (pages 190–203)

      Fuzhang Wu, Weiming Dong, Yan Kong, Xing Mei, Jean-Claude Paul and Xiaopeng Zhang

      Version of Record online: 11 JAN 2013 | DOI: 10.1111/cgf.12008

      Thumbnail image of graphical abstract

      This paper presents a novel content-based method for transferring the colour patterns between images. Unlike previous methods that rely on image colour statistics, our method puts an emphasis on high level scene content analysis. We first automatically extract the foreground subject areas and background scene layout from the scene. The semantic correspondences of the regions between source and target images are established. In the second step, the source image is re-coloured in a novel optimization framework, which incorporates the extracted content information and the spatial distributions of the target colour styles.

    15. Simulation of Morphology Changes in Drying Leaves (pages 204–215)

      SoHyeon Jeong, Si-Hyung Park and Chang-Hun Kim

      Version of Record online: 21 JAN 2013 | DOI: 10.1111/cgf.12009

      Thumbnail image of graphical abstract

      We introduce a biologically motivated simulation technique for the realistic shape deformation of drying leaves. In contrast to skeleton-based leaf deformation, our approach simulates the whole leaf surface to capture the fine details of desiccated leaves. We represent a leaf as a triangulated double-layer structure that consists of a Delaunay triangulation discretized along the vein structure and its corresponding Voronoi diagram. This structure can generate not only sharp creases along leaf veins, but also the complicated curling and crumpling on the leaf surface. The loss of water is the major factor that controls the inhomogeneous shrinkage of drying leaves.

  4. Reports

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Reports
    6. Erratum
    1. 2013 Cover Image: Prism (pages 216–217)

      Ben Spencer and Mark W. Jones

      Version of Record online: 21 FEB 2013 | DOI: 10.1111/cgf.12017

    2. Publisher's Note (page 218)

      Version of Record online: 21 FEB 2013 | DOI: 10.1111/cgf.12018

  5. Erratum

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Reports
    6. Erratum
    1. You have free access to this content
      Erratum (page 219)

      Version of Record online: 6 DEC 2012 | DOI: 10.1111/cgf.12002

      This article corrects:

      Visualization of 4D Blood-Flow Fields by Spatiotemporal Hierarchical Clustering

      Vol. 31, Issue 3pt2, 1065–1074, Version of Record online: 25 JUN 2012

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