28-Issue 8

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https://diglib.eg.org/handle/10.2312/150

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Interactive Graphics for Computer Adaptive Testing
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Cheng, I.; Basu, A.
Interactive graphics are commonly used in games and have been shown to be successful in attracting the general audience. Instead of computer games, animations, cartoons, and videos being used only for entertainment, there is now an interest in using interactive graphics for innovative testing . Rather than traditional pen-and-paper tests, audio, video and graphics are being conceived as alternative means for more effective testing in the future. In this paper, we review some examples of graphics item types for testing. As well, we outline how games can be used to interactively test concepts; discuss designing chemistry item types with interactive 3D graphics; suggest approaches for automatically adjusting difficulty level in interactive graphics based questions; and propose strategies for giving partial marks for incorrect answers. We study how to test different cognitive skills, such as music, using multimedia interfaces; and also evaluate the effectiveness of our model. Methods for estimating difficulty level of a mathematical item type using Item Response Theory (IRT) and a molecule construction item type using Graph Edit Distance are discussed. Evaluation of the graphics item types through extensive testing on some students is described. We also outline the application of using interactive graphics over cell phones. All of the graphics item types used in this paper are developed by members of our research group.
Fast Isosurface Rendering on a GPU by Cell Rasterization
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Liu, B.; Clapworthy, G. J.; Dong, F.
This paper presents a fast, high-quality, GPU-based isosurface rendering pipeline for implicit surfaces defined by a regular volumetric grid. GPUs are designed primarily for use with polygonal primitives, rather than volume primitives, but here we directly treat each volume cell as a single rendering primitive by designing a vertex program and fragment program on a commodity GPU. Compared with previous raycasting methods, ours has a more effective memory footprint (cache locality) and better coherence between multiple parallel SIMD processors. Furthermore, we extend and speed up our approach by introducing a new view-dependent sorting algorithm to take advantage of the early-z-culling feature of the GPU to gain significant performance speed-up. As another advantage, this sorting algorithm makes multiple transparent isosurfaces rendering available almost for free. Finally, we demonstrate the effectiveness and quality of our techniques in several real-time rendering scenarios and include analysis and comparisons with previous work.
Instant Caching for Interactive Global Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Debattista, K.; Dubla, P.; Banterle, F.; Santos, L.P.; Chalmers, A.
The ability to interactively render dynamic scenes with global illumination is one of the main challenges in computer graphics. The improvement in performance of interactive ray tracing brought about by significant advances in hardware and careful exploitation of coherence has rendered the potential of interactive global illumination a reality. However, the simulation of complex light transport phenomena, such as diffuse interreflections, is still quite costly to compute in real time. In this paper we present a caching scheme, termed Instant Caching, based on a combination of irradiance caching and instant radiosity. By reutilising calculations from neighbouring computations this results in a speedup over previous instant radiosity-based approaches. Additionally, temporal coherence is exploited by identifying which computations have been invalidated due to geometric transformations and updating only those paths. The exploitation of spatial and temporal coherence allows us to achieve superior frame rates for interactive global illumination within dynamic scenes, without any precomputation or quality loss when compared to previous methods; handling of lighting and material changes are also demonstrated.
Semi-Uniform Adaptive Patch Tessellation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Dyken, C.; Reimers, M.; Seland, J.
We present an adaptive tessellation scheme for surfaces consisting of parametric patches. The resulting tessellations are topologically uniform, yet consistent and watertight across boundaries of patches with different tessellation levels. Our scheme is simple to implement, requires little memory and is well suited for instancing, a feature available on current Graphical Processing Units that allows a substantial performance increase. We describe how the scheme can be implemented efficiently and give performance benchmarks comparing it to some other approaches.
Time-Adaptive Lines for the Interactive Visualization of Unsteady Flow Data Sets
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Cuntz, N.; Pritzkau, A.; Kolb, A.
The quest for the ideal flow visualization reveals two major challenges: interactivity and accuracy. Interactivity stands for explorative capabilities and real-time control. Accuracy is a prerequisite for every professional visualization in order to provide a reliable base for analysis of a data set. Geometric flow visualization has a long tradition and comes in very different flavors. Among these, stream, path and streak lines are known to be very useful for both 2D and 3D flows. Despite their importance in practice, appropriate algorithms suited for contemporary hardware are rare. In particular, the adaptive construction of the different line types is not sufficiently studied. This study provides a profound representation and discussion of stream, path and streak lines. Two algorithms are proposed for efficiently and accurately generating these lines using modern graphics hardware. Each includes a scheme for adaptive time-stepping. The adaptivity for stream and path lines is achieved through a new processing idea we call selective transform feedback . The adaptivity for streak lines combines adaptive time-stepping and a geometric refinement of the curve itself. Our visualization is applied, among others, to a data set representing a simulated typhoon. The storage as a set of 3D textures requires special attention. Both algorithms explicitly support this storage, as well as the use of precomputed adaptivity information.
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.
Interactive Fibre Structure Visualization of the Heart
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Peeters, T. H. J. M.; Vilanova, A.; Romeny, B. M. ter Haar
The heart consists of densely packed muscle fibres. The orientation of these fibres can be acquired by using Diffusion Tensor Imaging (DTI) ex vivo. A good way to visualize the fibre structure in a cross section of the heart is by showing short line segments originating from the cross section and aligned with the local direction of the fibres. If the line segments are placed dense enough, one can see how the fibre orientations change. However, generation of the line segments takes time and thus the user has to wait for new geometry to be generated when the plane defining the cross section is changed. We present a new direct rendering method for the visualization of the 3D vector field in a 2D user-definable cross section of a heart. On the intersection of the plane with the vector field, the full 3D vectors are rendered as 3D line segments with a local ray casting approach. No preprocessing of the data is needed and no geometry is generated. This technique allows a fast inspection of the data to identify interesting areas where further analysis is necessary (e.g. quantification or generation of streamlines). We also show how the technique is generalized to other glyph shapes than line segments by implementing ellipsoids.
Erratum
(The Eurographics Association and Blackwell Publishing Ltd, 2009)
Fast Four-Way Parallel Radix Sorting on GPUs
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ha, Linh; Krueger, Jens; Silva, Claudio T.
Efficient sorting is a key requirement for many computer science algorithms. Acceleration of existing techniques as well as developing new sorting approaches is crucial for many real-time graphics scenarios, database systems, and numerical simulations to name just a few. It is one of the most fundamental operations to organize and filter the ever growing massive amounts of data gathered on a daily basis. While optimal sorting models for serial execution on a single processor exist, efficient parallel sorting remains a challenge. In this paper, we present a hardware-optimized parallel implementation of the radix sort algorithm that results in a significant speed up over existing sorting implementations. We outperform all known General Processing Unit (GPU) based sorting systems by about a factor of two and eliminate restrictions on the sorting key space. This makes our algorithm not only the fastest, but also the first general GPU sorting solution.
Adaptive Interleaved Sampling for Interactive High-Fidelity Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Dubla, P.; Debattista, K.; Chalmers, A.
Recent advances have made interactive ray tracing (IRT) possible on consumer desktop machines. These advances have brought about the potential for interactive global illumination (IGI) with enhanced realism through physically based lighting. IGI, unlike IRT, has a much higher computational complexity. Furthermore, since non-primary rays constitute the majority of the computation, the rays are predominantly incoherent, making impractical many of the methods that have made IRT possible. Two methods that have already shown promise in decreasing the computational time of the GI solution are interleaved sampling and adaptive rendering. Interleaved sampling is a generalized sampling scheme that smoothly blends between regular and irregular sampling while maintaining coherence. Adaptive rendering algorithms adjust rendering quality, non-uniformally, using a guidance scheme. While adaptive rendering has shown to provide speed-up when used for off-line rendering it has not been utilized in IRT due to its naturally incoherent nature. In this paper, we combine adaptive rendering and interleaved sampling within a component-based solution into a new approach we term adaptive interleaved sampling. This allows us to tailor new adaptive heuristics for interleaved sampling of the individual components of the GI solution significantly improving overall performance. We present a novel component-based IGI framework for which we achieve interactive frame rates for a range of effects such as indirect diffuse lighting, soft shadows and single scatter homogeneous participating media.
Volumetric Billboards
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Decaudin, Philippe; Neyret, Fabrice
We introduce an image-based representation, called volumetric billboards, allowing for the real-time rendering of semi-transparent and visually complex objects arbitrarily distributed in a 3D scene. Our representation offers full parallax effect from any viewing direction and improved anti-aliasing of distant objects. It correctly handles transparency between multiple and possibly overlapping objects without requiring any primitive sorting. Furthermore, volumetric billboards can be easily integrated into common rasterization-based renderers, which allows for their concurrent use with polygonal models and standard rendering techniques such as shadow-mapping.The representation is based on volumetric images of the objects and on a dedicated real-time volume rendering algorithm that takes advantage of the GPU geometry shader. Our examples demonstrate the applicability of the method in many cases including levels-of-detail representation for multiple intersecting complex objects, volumetric textures, animated objects and construction of high-resolution objects by assembling instances of low-resolution volumetric billboards.
Bounding Volume Hierarchies of Slab Cut Balls
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Larsson, T.; Akenine-Moeller, T.
We introduce a bounding volume hierarchy based on the Slab Cut Ball. This novel type of enclosing shape provides an attractive balance between tightness of fit, cost of overlap testing, and memory requirement. The hierarchy construction algorithm includes a new method for the construction of tight bounding volumes in worst case O(n) time, which means our tree data structure is constructed in O(n log A n) time using traditional top-down building methods. A fast overlap test method between two slab cut balls is also proposed, requiring as few as 28-99 arithmetic operations, including the transformation cost. Practical collision detection experiments confirm that our tree data structure is amenable for high performance collision queries. In all the tested benchmarks, our bounding volume hierarchy consistently gives performance improvements over the sphere tree, and it is also faster than the OBB tree in five out of six scenes. In particular, our method is asymptotically faster than the sphere tree, and it also outperforms the OBB tree, in close proximity situations.
A Shape Grammar for Developing Glyph-based Visualizations
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Karnick, P.; Jeschke, S.; Cline, D.; Razdan, A.; Wentz, E.; Wonka, P.
In this paper we address the question of how to quickly model glyph-based Geographic Information System visualizations. Our solution is based on using shape grammars to set up the different aspects of a visualization, including the geometric content of the visualization, methods for resolving layout conflicts and interaction methods. Our approach significantly increases modelling efficiency over similarly flexible systems currently in use.
Autostereoscopic Rendering of Multiple Light Fields
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Escriva, M.; Blasco, J.; Abad, F.; Camahort, E.; Vivo, R.
Light fields were introduced a decade ago as a new high-dimensional graphics rendering model. However, they have not been thoroughly used because their applications are very specific and their storage requirements are too high. Recently, spatial imaging devices have been related to light fields. These devices allow several users to see three-dimensional (3D) images without using glasses or other intrusive elements.This paper presents a light-field model that can be rendered in an autostereoscopic spatial device. The model is viewpoint-independent and supports continuous multiresolution, foveal rendering, and integrating multiple light fields and geometric models in the same scene.We also show that it is possible to examine interactively a scene composed of several light fields and geometric models. Visibility is taken care of by the algorithm. Our goal is to apply our models to 3D TV and spatial imaging.
A Bayesian Monte Carlo Approach to Global Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Brouillat, Jonathan; Bouville, Christian; Loos, Brad; Hansen, Charles; Bouatouch, Kadi
Most Monte Carlo rendering algorithms rely on importance sampling to reduce the variance of estimates. Importance sampling is efficient when the proposal sample distribution is well-suited to the form of the integrand but fails otherwise. The main reason is that the sample location information is not exploited. All sample values are given the same importance regardless of their proximity to one another. Two samples falling in a similar location will have equal importance whereas they are likely to contain redundant information. The Bayesian approach we propose in this paper uses both the location and value of the data to infer an integral value based on a prior probabilistic model of the integrand. The Bayesian estimate depends only on the sample values and locations, and not how these samples have been chosen. We show how this theory can be applied to the final gathering problem and present results that clearly demonstrate the benefits of Bayesian Monte Carlo.
g-BRDFs: An Intuitive and Editable BTF Representation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Menzel, N.; Guthe, M.
Measured reflection data such as the bidirectional texture function (BTF) represent spatial variation under the full hemisphere of view and light directions and offer a very realistic visual appearance. Despite its high-dimensional nature, recent compression techniques allow rendering of BTFs in real time. Nevertheless, a still unsolved problem is that there is no representation suited for real-time rendering that can be used by designers to modify the BTF s appearance. For intuitive editing, a set of low-dimensional comprehensible parameters, stored as scalars, colour values or texture maps, is required. In this paper we present a novel way to represent BTF data by introducing the geometric BRDF (g-BRDF), which describes both the underlying meso- and micro-scale structure in a very compact way. Both are stored in texture maps with only a few additional scalar parameters that can all be modified at runtime and thus give the designer full control over the material s appearance in the final real-time application. The g-BRDF does not only allow intuitive editing, but also reduces the measured data into a small set of textures, yielding a very effective compression method. In contrast to common material representation combining heightfields and BRDFs, our g-BRDF is physically based and derived from direct measurement, thus representing real-world surface appearance. In addition, we propose an algorithm for fully automatic decomposition of a given measured BTF into the g-BRDF representation.
Robust and Efficient Surface Reconstruction From Range Data
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Labatut, P.; Pons, J.-P.; Keriven, R.
We describe a robust but simple algorithm to reconstruct a surface from a set of merged range scans. Our key contribution is the formulation of the surface reconstruction problem as an energy minimisation problem that explicitly models the scanning process. The adaptivity of the Delaunay triangulation is exploited by restricting the energy to inside/outside labelings of Delaunay tetrahedra. Our energy measures both the output surface quality and how well the surface agrees with soft visibility constraints. Such energy is shown to perfectly fit into the minimum s - t cuts optimisation framework, allowing fast computation of a globally optimal tetrahedra labeling, while avoiding the shrinking bias that usually plagues graph cuts methods.The behaviour of our method confronted to noise, undersampling and outliers is evaluated on several data sets and compared with other methods through different experiments: its strong robustness would make our method practical not only for reconstruction from range data but also from typically more difficult dense point clouds, resulting for instance from stereo image matching. Our effective modeling of the surface acquisition inverse problem, along with the unique combination of Delaunay triangulation and minimum s - t cuts, makes the computational requirements of the algorithm scale well with respect to the size of the input point cloud.
Table of Contents and Cover
(The Eurographics Association and Blackwell Publishing Ltd, 2009)
Interactive Pixel-Accurate Free Viewpoint Rendering from Images with Silhouette Aware Sampling
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Hornung, A.; Kobbelt, L.
We present an integrated, fully GPU-based processing pipeline to interactively render new views of arbitrary scenes from calibrated but otherwise unstructured input views. In a two-step procedure, our method first generates for each input view a dense proxy of the scene using a new multi-view stereo formulation. Each scene proxy consists of a structured cloud of feature aware particles which automatically have their image space footprints aligned to depth discontinuities of the scene geometry and hence effectively handle sharp object boundaries and occlusions. We propose a particle optimization routine combined with a special parameterization of the view space that enables an efficient proxy generation as well as robust and intuitive filter operators for noise and outlier removal. Moreover, our generic proxy generation allows us to flexibly handle scene complexities ranging from small objects up to complete outdoor scenes. The second phase of the algorithm combines these particle clouds in real-time into a view-dependent proxy for the desired output view and performs a pixel-accurate accumulation of the colour contributions from each available input view. This makes it possible to reconstruct even fine-scale view-dependent illumination effects. We demonstrate how all these processing stages of the pipeline can be implemented entirely on the GPU with memory efficient, scalable data structures for maximum performance. This allows us to generate new output renderings of high visual quality from input images in real-time.
Replica Exchange Light Transport
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Kitaoka, Shinya; Kitamura, Yoshifumi; Kishino, Fumio
We solve the light transport problem by introducing a novel unbiased Monte Carlo algorithm called replica exchange light transport, inspired by the replica exchange Monte Carlo method in the fields of computational physics and statistical information processing. The replica exchange Monte Carlo method is a sampling technique whose operation resembles simulated annealing in optimization algorithms using a set of sampling distributions. We apply it to the solution of light transport integration by extending the probability density function of an integrand of the integration to a set of distributions. That set of distributions is composed of combinations of the path densities of different path generation types: uniform distributions in the integral domain, explicit and implicit paths in light (particle/photon) tracing, indirect paths in bidirectional path tracing, explicit and implicit paths in path tracing, and implicit caustics paths seen through specular surfaces including the delta function in path tracing. The replica-exchange light transport algorithm generates a sequence of path samples from each distribution and samples the simultaneous distribution of those distributions as a stationary distribution by using the Markov chain Monte Carlo method. Then the algorithm combines the obtained path samples from each distribution using multiple importance sampling. We compare the images generated with our algorithm to those generated with bidirectional path tracing and Metropolis light transport based on the primary sample space. Our proposing algorithm has better convergence property than bidirectional path tracing and the Metropolis light transport, and it is easy to implement by extending the Metropolis light transport.

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