Computer Graphics Forum

Cover image for Vol. 33 Issue 1

February 2014

Volume 33, Issue 1

Pages i–ii, 1–306

  1. Issue Information

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

      Version of Record online: 24 FEB 2014 | DOI: 10.1111/cgf.12338

  2. Editorial

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Report
    1. Editorial (page 1)

      Holly Rushmeier and Oliver Deussen

      Version of Record online: 24 FEB 2014 | DOI: 10.1111/cgf.12339

  3. Articles

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Report
    1. Mobility-Trees for Indoor Scenes Manipulation (pages 2–14)

      Andrei Sharf, Hui Huang, Cheng Liang, Jiapei Zhang, Baoquan Chen and Minglun Gong

      Version of Record online: 16 SEP 2013 | DOI: 10.1111/cgf.12204

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      In this work, we introduce the ‘mobility-tree’ construct for high-level functional representation of complex 3D indoor scenes. In recent years, digital indoor scenes are becoming increasingly popular, consisting of detailed geometry and complex functionalities. These scenes often consist of objects that reoccur in various poses and interrelate with each other. In this work we analyse the reoccurrence of objects in the scene and automatically detect their functional mobilities. ‘Mobility’ analysis denotes the motion capabilities (i.e. degree of freedom) of an object and its subpart which typically relates to their indoor functionalities. We compute an object's mobility by analysing its spatial arrangement, repetitions and relations with other objects and store it in a ‘mobility-tree’.

    2. Appearance Stylization of Manhattan World Buildings (pages 15–26)

      C. Li, P. J. Willis and M. Brown

      Version of Record online: 10 OCT 2013 | DOI: 10.1111/cgf.12251

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      We propose a method that generates stylized building models from examples. Our method only requires minimal user input to capture the appearance of a Manhattan world building, and can automatically retarget the captured “look and feel” to new models. The key contribution is a novel representation, namely the “style sheet”, that is captured independently from a building's structure. It summarizes characteristic shape and texture patterns on the building. In the retargeting stage, a style sheet is used to decorate new buildings of potentially different structures. Consistent face groups are proposed to capture complex texture patterns from the example model and to preserve the patterns in the retarget models.

    3. A Survey of Volumetric Illumination Techniques for Interactive Volume Rendering (pages 27–51)

      Daniel Jönsson, Erik Sundén, Anders Ynnerman and Timo Ropinski

      Version of Record online: 10 OCT 2013 | DOI: 10.1111/cgf.12252

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      Interactive volume rendering in its standard formulation has become an increasingly important tool in many application domains. In recent years several advanced volumetric illumination techniques to be used in interactive scenarios have been proposed. These techniques claim to have perceptual benefits as well as being capable of producing more realistic volume rendered images. Naturally, they cover a wide spectrum of illumination effects, including varying shading and scattering effects. In this survey, we review and classify the existing techniques for advanced volumetric illumination. The classification will be conducted based on their technical realization, their performance behavior as well as their perceptual capabilities.

    4. Visualization of the Centre of Projection Geometrical Locus in a Single Image (pages 52–63)

      V. Stojaković, S. Popov and B. Tepavčević

      Version of Record online: 16 OCT 2013 | DOI: 10.1111/cgf.12253

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      Users usually do not fully understand the SVR process, which is why they have trouble in decision making while modelling. That often fundamentally affects the quality of the final 3D models. We introduce a tool set for 3D visualisation of the CP's geometrical loci that provides the user with a clear idea of how the CP's location is determined. Evaluation proves that Tool set provides an effective improvement.

    5. Controlled Metamorphosis Between Skeleton-Driven Animated Polyhedral Meshes of Arbitrary Topologies (pages 64–72)

      Denis Kravtsov, Oleg Fryazinov, Valery Adzhiev, Alexander Pasko and Peter Comninos

      Version of Record online: 18 OCT 2013 | DOI: 10.1111/cgf.12254

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      Enabling animators to smoothly transform between animated meshes of differing topologies is a long-standing problem in geometric modelling and computer animation. In this paper, we propose a new hybrid approach built upon the advantages of scalar field-based models (often called implicit surfaces) which can easily change their topology by changing their defining scalar field. Given two meshes, animated by their rigging-skeletons, we associate each mesh with its own approximating implicit surface. This implicit surface moves synchronously with the mesh. The shape-metamorphosis process is performed in several steps: first, we collapse the two meshes to their corresponding approximating implicit surfaces, then we transform between the two implicit surfaces.

    6. Robust Segmentation of Multiple Intersecting Manifolds from Unoriented Noisy Point Clouds (pages 73–87)

      J. Kustra, A. Jalba and A. Telea

      Version of Record online: 12 DEC 2013 | DOI: 10.1111/cgf.12255

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      We present a method for extracting complex manifolds with an arbitrary number of (self) intersections from unoriented point clouds containing large amounts of noise. Manifolds are formed in a three step process. First, small flat neighborhoods of all possible orientations are created around all points. Next, neighborhoods are assembled into larger quasi-flat patches, whose overlaps determine the global connectivity structure of the point cloud. Finally, curved manifolds, as well as their intersection curves, are extracted from the patch connectivity graph via a multiple-source flood fill. The extracted manifolds can be straightforwardly reconstructed into polygonal surfaces using standard surface reconstruction methods.

    7. Scalable Realistic Rendering with Many-Light Methods (pages 88–104)

      Carsten Dachsbacher, Jaroslav Křivánek, Miloš Hašan, Adam Arbree, Bruce Walter and Jan Novák

      Version of Record online: 14 NOV 2013 | DOI: 10.1111/cgf.12256

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      Recent years have seen increasing attention and significant progress in many-light rendering, a class of methods for efficient computation of global illumination. The many-light formulation offers a unified mathematical framework for the problem reducing the full lighting transport simulation to the calculation of the direct illumination from many virtual light sources. These methods are unrivaled in their scalability: they are able to produce plausible images in a fraction of a second but also converge to the full solution over time. In this state-of-the-art report, we give an easy-to-follow, introductory tutorial of the many-light theory.

    8. Visibility Silhouettes for Semi-Analytic Spherical Integration (pages 105–117)

      Derek Nowrouzezahrai, Ilya Baran, Kenny Mitchell and Wojciech Jarosz

      Version of Record online: 14 NOV 2013 | DOI: 10.1111/cgf.12257

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      At each shade point, the spherical visibility function encodes occlusion from surrounding geometry, in all directions. Computing this function is difficult and point-sampling approaches, such as ray-tracing or hardware shadow mapping, are traditionally used to efficiently approximate it. We propose a semi-analytic solution to the problem where the spherical silhouette of the visibility is computed using a search over a 4D dual mesh of the scene. Once computed, we are able to semi-analytically integrate visibility-masked spherical functions along the visibility silhouette, instead of over the entire hemisphere. In this way, we avoid the artifacts that arise from using point-sampling strategies to integrate visibility, a function with unbounded frequency content.

    9. You have full text access to this OnlineOpen article
      Subdivision Surfaces with Creases and Truncated Multiple Knot Lines (pages 118–128)

      J. Kosinka, M. A. Sabin and N. A. Dodgson

      Version of Record online: 15 NOV 2013 | DOI: 10.1111/cgf.12258

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      We deal with subdivision schemes based on arbitrary degree B-splines. We focus on extraordinary knots which exhibit various levels of complexity in terms of both valency and multiplicity of knot lines emanating from such knots. The purpose of truncated multiple knot lines is to model creases which fair out. Our construction supports any degree and any knot line multiplicity and provides a modelling framework familiar to users used to B-splines and NURBS systems.

    10. Stackless Multi-BVH Traversal for CPU, MIC and GPU Ray Tracing (pages 129–140)

      Attila T. Áfra and László Szirmay-Kalos

      Version of Record online: 20 NOV 2013 | DOI: 10.1111/cgf.12259

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      Stackless traversal algorithms for ray tracing acceleration structures require significantly less storage per ray than ordinary stack-based ones. This advantage is important for massively parallel rendering methods, where there are many rays in flight. On SIMD architectures, a commonly used acceleration structure is the multi bounding volume hierarchy (MBVH), which has multiple bounding boxes per node for improved parallelism. It scales to branching factors higher than two, for which, however, only stack-based traversal methods have been proposed so far. In this paper, we introduce a novel stackless traversal algorithm for MBVHs with up to 4-way branching.

    11. Implicit Decals: Interactive Editing of Repetitive Patterns on Surfaces (pages 141–151)

      Erwin de Groot, Brian Wyvill, Loïc Barthe, Ahmad Nasri and Paul Lalonde

      Version of Record online: 24 DEC 2013 | DOI: 10.1111/cgf.12260

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      Texture mapping is an essential component for creating 3D models and is widely used in both the game and the movie industries. Creating texture maps has always been a complex task and existing methods carefully balance flexibility with ease of use. One difficulty in using texturing is the repeated placement of individual textures over larger areas. In this paper we propose a method which uses decals to place images onto a model. Our method allows the decals to compete for space and to deform as they are being pushed by other decals.

    12. Projection Mapping on Arbitrary Cubic Cell Complexes (pages 152–163)

      K. Apaza-Agüero, L. Silva and O. R. P.  Bellon

      Version of Record online: 24 DEC 2013 | DOI: 10.1111/cgf.12261

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      This work presents a new representation used as a rendering primitive of surfaces. Our representation is defined by an arbitrary cubic cell complex: a projection-based parameterization domain for surfaces where geometry and appearance information are stored as tile textures. This representation is used by our ray casting rendering algorithm called projection mapping, which can be used for rendering geometry and appearance details of surfaces from arbitrary viewpoints. Alternatively, another method is proposed for mapping appearance information on complex surfaces using our arbitrary cubic cell complexes. In this case, instead of reconstructing the geometry as in projection mapping, the original mesh of a surface is directly passed to the rendering algorithm.

    13. Multi-Scale Kernels Using Random Walks (pages 164–177)

      A. Sinha and K. Ramani

      Version of Record online: 21 NOV 2013 | DOI: 10.1111/cgf.12264

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      We introduce novel multi-scale kernels using the random walk framework and derive corresponding embeddings and pairwise distances. The fractional moments of the rate of continuous time random walk (equivalently diffusion rate) are used to discover higher order kernels (or similarities) between pair of points. The formulated kernels are isometry, scale and tessellation invariant, can be made globally or locally shape aware and are insensitive to partial objects and noise based on the moment and influence parameters. In addition, the corresponding kernel distances and embeddings are convergent and efficiently computable.

    14. Image Space Rendering of Point Clouds Using the HPR Operator (pages 178–189)

      R. Machado e Silva, C. Esperança, R. Marroquim and A. A. F. Oliveira

      Version of Record online: 30 NOV 2013 | DOI: 10.1111/cgf.12265

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      The hidden point removal (HPR) operator introduced by Katz et al. [KTB07] provides an elegant solution for the problem of estimating the visibility of points in point samplings of surfaces. Since the method requires computing the three-dimensional convex hull of a set with the same cardinality as the original cloud, the method has been largely viewed as impractical for real-time rendering of medium to large clouds. In this paper we examine how the HPR operator can be used more efficiently by combining several image space techniques, including an approximate convex hull algorithm, cloud sampling, and GPU programming. Experiments show that this combination permits faster renderings without overly compromising the accuracy.

    15. Modelling of Non-Periodic Aggregates Having a Pile Structure (pages 190–198)

      K. Sakurai and K. Miyata

      Version of Record online: 30 NOV 2013 | DOI: 10.1111/cgf.12266

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      This paper presents a procedure for modelling aggregates such as piles that consist of arbitrary components. The method generates an aggregate of components that need to be accumulated, and an aggregate shape represents the surface of the target aggregate. The number of components and their positions and orientations are controlled by five parameters. The components, the aggregate shape and the parameters are the inputs for the method which involves placement and refinement steps. In the placement step, the orientation and initial position of a component are determined by a non-periodic placement such that each component overlaps its neighbours. In the refinement step, to construct a pile structure, the position of each component is adjusted by reducing the overlap.

    16. Low-Cost Subpixel Rendering for Diverse Displays (pages 199–209)

      Thomas Engelhardt, Thorsten-Walther Schmidt, Jan Kautz and Carsten Dachsbacher

      Version of Record online: 10 DEC 2013 | DOI: 10.1111/cgf.12267

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      Subpixel rendering increases the apparent display resolution by taking into account the subpixel structure of a given display. In essence, each subpixel is addressed individually, allowing the underlying signal to be sampled more densely. Unfortunately, naïve subpixel sampling introduces colour aliasing, as each subpixel only displays a specific colour (usually R, G, and B subpixels are used). As previous work has shown, chromatic aliasing can be reduced significantly by taking the sensitivity of the human visual system into account. In this work, wefind optimal filters for subpixel rendering for a diverse set of 1D and 2D subpixel layout patterns.

    17. On Perception of Semi-Transparent Streamlines for Three-Dimensional Flow Visualization (pages 210–221)

      O. Mishchenko and R. Crawfis

      Version of Record online: 30 NOV 2013 | DOI: 10.1111/cgf.12268

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      One of the standard techniques to visualize three-dimensional flow is to use geometry primitives. This solution, when opaque primitives are used, results in high levels of occlusion, especially with dense streamline seeding. Using semi-transparent geometry primitives can alleviate the problem of occlusion. However, with semi-transparency some parts of the data set become too vague and blurry, while others are still heavily occluded. We conducted a user study that provided us with results on perceptual limits of using semi-transparent geometry primitives for flow visualization. Texture models for semi-transparent streamlines were introduced. Test subjects were shown multiple overlaying layers of streamlines and recorded how many different flow directions they were able to perceive. The user study allowed us to identify a set of top scoring textures. We discuss the results of the user study, provide guidelines on using semi-transparency for three-dimensional flow visualization and show how varying textures for different streamlines can further enhance the perception of dense streamlines. We also discuss the strategies for dealing with very high levels of occlusion. The strategies are per-pixel filtering of flow directions, when only some of the streamlines are rendered at a particular pixel, and opacity normalization, a way of altering the opacity of overlapping streamlines with the same direction. We illustrate our results with a variety of visualizations.

    18. Time Line Cell Tracking for the Approximation of Lagrangian Coherent Structures with Subgrid Accuracy (pages 222–234)

      A. Kuhn, W. Engelke, C. Rössl, M. Hadwiger and H. Theisel

      Version of Record online: 5 DEC 2013 | DOI: 10.1111/cgf.12269

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      Lagrangian Coherent Structures (LCS) have become a widespread and powerful method to describe dynamic motion patterns in time-dependent flow fields. The standard way to extract LCS is to compute height ridges in the Finite Time Lyapunov Exponent (FTLE) field. In this work, we present an alternative method to approximate Lagrangian features for 2D unsteady flow fields that achieves subgrid accuracy without additional particle sampling. We obtain this by a geometric reconstruction of the flow map using additional material constraints for the available samples. The illustration shows four approximations of LCS at different time steps in subgrid accuracy computed from a triangular grid containing 60 times 120 sample points for a heated cylinder simulation.

    19. Occluder Simplification Using Planar Sections (pages 235–245)

      Ari Silvennoinen, Hannu Saransaari, Samuli Laine and Jaakko Lehtinen

      Version of Record online: 15 DEC 2013 | DOI: 10.1111/cgf.12271

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      We present a method for extreme occluder simplification. We take a triangle soup as input, and produce a small set of polygons with closely matching occlusion properties. In contrast to methods that optimize the original geometry, our algorithm has very few requirements for the input— specifically, the input does not need to be a watertight, two-manifold mesh. This robustness is achieved by working on a well-behaved, discretized representation of the input instead of the original, potentially badly structured geometry. We first formulate the algorithm for individual occluders, and further introduce a hierarchy for handling large, complex scenes.

    20. Interactive Simulation of Rigid Body Dynamics in Computer Graphics (pages 246–270)

      Jan Bender, Kenny Erleben and Jeff Trinkle

      Version of Record online: 10 DEC 2013 | DOI: 10.1111/cgf.12272

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      Interactive rigid body simulation is an important part of many modern computer tools, which no authoring tool nor game engine can do without. Such high performance computer tools open up new possibilities for changing how designers, engineers, modelers and animators work with their design problems. This paper is a self contained state-of-the-art report on the physics, the models, the numerical methods and the algorithms used in interactive rigid body simulation all of which have evolved and matured over the past 20 years. Furthermore, the paper communicates the mathematical and theoretical details in a pedagogical manner.

    21. On Near Optimal Lattice Quantization of Multi-Dimensional Data Points (pages 271–281)

      M. Finckh, H. Dammertz and H. P. A. Lensch

      Version of Record online: 21 DEC 2013 | DOI: 10.1111/cgf.12273

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      One of the most elementary application of a lattice is the quantization of real valued s-dimensional vectors into finite bit precision to make them representable by a digital computer. Most often, the simple s-dimensional regular grid is used for this task where each component of the vector is quantized individually. However, it is known that other lattices perform better regarding the average quantization error. A rank-1 lattices is a special type of lattice, where the lattice points can be described by a single s-dimensional generator vector.

    22. Boosting Techniques for Physics-Based Vortex Detection (pages 282–293)

      L. Zhang, Q. Deng, R. Machiraju, A. Rangarajan, D. Thompson, D. K. Walters and H.-W. Shen

      Version of Record online: 15 JAN 2014 | DOI: 10.1111/cgf.12275

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      Robust automated vortex detection algorithms are needed to facilitate the exploration of large-scale turbulent fluid flow simulations. Unfortunately, robust non-local vortex detection algorithms are computationally intractable for large data sets and local algorithms, while computationally tractable, lack robustness. We argue that the deficiencies inherent to the local definitions occur because of two fundamental issues: the lack of a rigorous definition of a vortex and the fact that a vortex is an intrinsically non-local phenomenon. As a first step towards addressing this problem, we demonstrate the use of machine learning techniques to enhance the robustness of local vortex detection algorithms.

    23. τέχνη Photons: Evolution of a Course in Data Structures (pages 294–304)

      A. T. Duchowski

      Version of Record online: 17 JAN 2014 | DOI: 10.1111/cgf.12279

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      This paper presents the evolution of a data structures and algorithms course based on a specific computer graphics problem, namely photon mapping, as the teaching medium. The paper reports development of the course through several iterations and evaluations, dating back five years.

  4. Report

    1. Top of page
    2. Issue Information
    3. Editorial
    4. Articles
    5. Report
    1. 2014 Cover Image: Supernova (pages 305–306)

      Marco Ament, Filip Sadlo and Daniel Weiskopf

      Version of Record online: 24 FEB 2014 | DOI: 10.1111/cgf.12337