Volume 29 (2010)

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Bidirectional Texture Function Compression Based on Multi-Level Vector Quantization
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Havran, V.; Filip, J.; Myszkowski, K.
The Bidirectional Texture Function (BTF) is becoming widely used for accurate representation of real-world material appearance. In this paper a novel BTF compression model is proposed. The model resamples input BTF data into a parametrization, allowing decomposition of individual view and illumination dependent texels into a set of multi-dimensional conditional probability density functions. These functions are compressed in turn using a novel multi-level vector quantization algorithm. The result of this algorithm is a set of index and scale code-books for individual dimensions. BTF reconstruction from the model is then based on fast chained indexing into the nested stored code-books. In the proposed model, luminance and chromaticity are treated separately to achieve further compression. The proposed model achieves low distortion and compression ratios 1:233-1:2040, depending on BTF sample variability. These results compare well with several other BTF compression methods with predefined compression ratios, usually smaller than 1:200. We carried out a psychophysical experiment comparing our method with LPCA method. BTF synthesis from the model was implemented on a standard GPU, yielded interactive framerates. The proposed method allows the fast importance sampling required by eye-path tracing algorithms in image synthesis.
Signing the Unsigned: Robust Surface Reconstruction from Raw Pointsets
(2010) Patrick Mullen; Fernando de Goes; Mathieu Desbrun; David Cohen-Steiner; Pierre Alliez
We propose a modular framework for robust 3D reconstruction from unorganized, unoriented, noisy, and outlierridden geometric data. We gain robustness and scalability over previous methods through an unsigned distance approximation to the input data followed by a global stochastic signing of the function. An isosurface reconstruction is finally deduced via a sparse linear solve. We show with experiments on large, raw, geometric datasets that this approach is scalable while robust to noise, outliers, and holes. The modularity of our approach facilitates customization of the pipeline components to exploit specific idiosyncracies of datasets, while the simplicity of each component leads to a straightforward implementation.
An Interactive Visual Analytics System for Bridge Management
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Wang, Xiaoyu; Dou, Wenwen; Chen, Shen-En; Ribarsky, William; Chang, Remco; G. Melancon, T. Munzner, and D. Weiskopf
Bridges deteriorate over their life cycles and require continuous maintenance to ensure their structural integrity, and in turn, the safety of the public. Maintaining bridges is a multi-faceted operation that requires both domain knowledge and analytics techniques over large data sources. Although most existing bridge management systems (BMS) are very efficient at data storage, they are not as effective at providing analytical capabilities or as flexible at supporting different inspection technologies. In this paper, we present a visual analytics system that extends the capability of current BMSs. Based on a nation-wide survey and our interviews with bridge managers, we designed our system to be customizable so that it can provide interactive exploration, information correlation, and domainoriented data analysis. When tested by bridge managers of the U.S. Department of Transportation, we validated that our system provides bridge managers with the necessary features for performing in-depth analysis of bridges from a variety of perspectives that are in accordance to their typical workflow.
Resampling Strategies for Deforming MLS Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Gois, Joao Paulo; Buscaglia, Gustavo C.
Moving-least-squares (MLS) surfaces undergoing large deformations need periodic regeneration of the point set (point-set resampling) so as to keep the point-set density quasi-uniform. Previous work by the authors dealt with algebraic MLS surfaces, and proposed a resampling strategy based on defining the new points at the intersections of the MLS surface with a suitable set of rays. That strategy has very low memory requirements and is easy to parallelize. In this article new resampling strategies with reduced CPU-time cost are explored. The basic idea is to choose as set of rays the lines of a regular, Cartesian grid, and to fully exploit this grid: as data structure for search queries, as spatial structure for traversing the surface in a continuation-like algorithm, and also as approximation grid for an interpolated version of the MLS surface. It is shown that in this way a very simple and compact resampling technique is obtained, which cuts the resampling cost by half with affordable memory requirements.
A Layered Particle-Based Fluid Model for Real-Time Rendering of Water
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Bagar, Florian; Scherzer, Daniel; Wimmer, Michael
We present a physically based real-time water simulation and rendering method that brings volumetric foam to the real-time domain, significantly increasing the realism of dynamic fluids. We do this by combining a particle-based fluid model that is capable of accounting for the formation of foam with a layered rendering approach that is able to account for the volumetric properties of water and foam. Foam formation is simulated through Weber number thresholding. For rendering, we approximate the resulting water and foam volumes by storing their respective boundary surfaces in depth maps. This allows us to calculate the attenuation of light rays that pass through these volumes very efficiently. We also introduce an adaptive curvature flow filter that produces consistent fluid surfaces from particles independent of the viewing distance.
Condenser-Based Instant Reflectometry
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lan, Yanxiang; Dong, Yue; Wang, Jiaping; Tong, Xin; Guo, Baining
We present a technique for rapid capture of high quality bidirectional reflection distribution functions(BRDFs) of surface points. Our method represents the BRDF at each point by a generalized microfacet model with tabulated normal distribution function (NDF) and assumes that the BRDF is symmetrical. A compact and light-weight reflectometry apparatus is developed for capturing reflectance data from each surface point within one second. The device consists of a pair of condenser lenses, a video camera, and six LED light sources. During capture, the reflected rays from a surface point lit by a LED lighting are refracted by a condenser lenses and efficiently collected by the camera CCD. Taking advantage of BRDF symmetry, our reflectometry apparatus provides an efficient optical design to improve the measurement quality. We also propose a model fitting algorithm for reconstructing the generalized microfacet model from the sparse BRDF slices captured from a material surface point. Our new algorithm addresses the measurement errors and generates more accurate results than previous work. Our technique provides a practical and efficient solution for BRDF acquisition, especially for materials with anisotropic reflectance. We test the accuracy of our approach by comparing our results with ground truth. We demonstrate the efficiency of our reflectometry by measuring materials with different degrees of specularity, values of Fresnel factor, and angular variation.
Practical quad mesh simplification
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Tarini, Marco; Pietroni, Nico; Cignoni, Paolo; Panozzo, Daniele; Puppo, Enrico
In this paper we present an innovative approach to incremental quad mesh simplification, i.e. the task of producing a low complexity quad mesh starting from a high complexity one. The process is based on a novel set of strictly local operations which preserve quad structure. We show how good tessellation quality (e.g. in terms of vertex valencies) can be achieved by pursuing uniform length and canonical proportions of edges and diagonals. The decimation process is interleaved with smoothing in tangent space. The latter strongly contributes to identify a suitable sequence of local modification operations. The method is naturally extended to manage preservation of feature lines (e.g. creases) and varying (e.g. adaptive) tessellation densities. We also present an original Triangle-to-Quad conversion algorithm that behaves well in terms of geometrical complexity and tessellation quality, which we use to obtain the initial quad mesh from a given triangle mesh.
Interactive Editing of Lighting and Materials using a Bivariate BRDF Representation
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Sitthi-Amorn, Pitchaya; Romeiro, Fabiano; Zickler, Todd; Lawrence, Jason
We present a new Precomputed Radiance Transfer (PRT) algorithm based on a two dimensional representation of isotropic BRDFs. Our approach involves precomputing matrices that allow quickly mapping environment lighting, which is represented in the global coordinate system, and the surface BRDFs, which are represented in a bivariate domain, to the local hemisphere at a surface location where the reflection integral is evaluated. When the lighting and BRDFs are represented in a wavelet basis, these rotation matrices are sparse and can be efficiently stored and combined with pre-computed visibility at run-time. Compared to prior techniques that also precompute wavelet rotation matrices, our method allows full control over the lighting and materials due to the way the BRDF is represented. Furthermore, this bivariate parameterization preserves sharp specular peaks and grazing effects that are attenuated in conventional parameterizations. We demonstrate a prototype rendering system that achieves real-time framerates while lighting and materials are edited.
A PCA Decomposition for Real-time BRDF Editing and Relighting with Global Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Nguyen, Chuong H.; Kyung, Min-Ho; Lee, Joo-Haeng; Nam, Seung-Woo
We propose a novel rendering method which supports interactive BRDF editing as well as relighting on a 3D scene. For interactive BRDF editing, we linearize an analytic BRDF model with basis BRDFs obtained from a principal component analysis. For each basis BRDF, the radiance transfer is precomputed and stored in vector form. In rendering time, illumination of a point is computed by multiplying the radiance transfer vectors of the basis BRDFs by the incoming radiance from gather samples and then linearly combining the results weighted by user-controlled parameters. To improve the level of accuracy, a set of sub-area samples associated with a gather sample refines the glossy reflection of the geometric details without increasing the precomputation time. We demonstrate this program with a number of examples to verify the real-time performance of relighting and BRDF editing on 3D scenes with complex lighting and geometry.
Brushing Moments in Interactive Visual Analysis
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Kehrer, Johannes; Filzmoser, Peter; Hauser, Helwig; G. Melancon, T. Munzner, and D. Weiskopf
We present a systematic study of opportunities for the interactive visual analysis of multi-dimensional scientific data that is based on the integration of statistical aggregations along selected independent data dimensions in a framework of coordinated multiple views (with linking and brushing). Traditional and robust estimates of the four statistical moments (mean, variance, skewness, and kurtosis) as well as measures of outlyingness are integrated in an iterative visual analysis process. Brushing particular statistics, the analyst can investigate data characteristics such as trends and outliers. We present a categorization of beneficial combinations of attributes in 2D scatterplots: (a) kth vs. (k+1)th statistical moment of a traditional or robust estimate, (b) traditional vs. robust version of the same moment, (c) two different robust estimates of the same moment. We propose selected view transformations to iteratively construct this multitude of informative views as well as to enhance the depiction of the statistical properties in scatterplots and quantile plots. In the framework, we interrelate the original distributional data and the aggregated statistics, which allows the analyst to work with both data representations simultaneously. We demonstrate our approach in the context of two visual analysis scenarios of multi-run climate simulations.
Polygonal Boundary Evaluation of Minkowski Sums and Swept Volumes
(2010) Marcel Campen; Leif Kobbelt
Abstract We present a novel technique for the efficient boundary evaluation of sweep operations applied to objects in polygonal boundary representation. These sweep operations include Minkowski addition, offsetting, and sweeping along a discrete rigid motion trajectory. Many previous methods focus on the construction of a polygonal superset (containing self-intersections and spurious internal geometry) of the boundary of the volumes which are swept. Only few are able to determine a clean representation of the actual boundary, most of them in a discrete volumetric setting. We unify such superset constructions into a succinct common formulation and present a technique for the robust extraction of a polygonal mesh representing the outer boundary, i.e. it makes no general position assumptions and always yields a manifold, watertight mesh. It is exact for Minkowski sums and approximates swept volumes polygonally. By using plane-based geometry in conjunction with hierarchical arrangement computations we avoid the necessity of arbitrary precision arithmetics and extensive special case handling. By restricting operations to regions containing pieces of the boundary, we significantly enhance the performance of the algorithm.
Dirichlet Harmonic Shape Compression with Feature Preservation for Parameterized Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Liu, Yang; Prabhakaran, Balakrishnan; Guo, Xiaohu
With the rapid advancement of 3D scanning devices, large and complicated 3D shapes are becoming ubiquitous, and require large amount of resources to store and transmit them efficiently. This makes shape compression a demanding technique in order for the user to reduce the data transmission latency. Existing shape compression methods could achieve very low bit-rates by sacrificing shape quality. But none of them guarantees the preservation of salient feature lines that users care. In addition, many 3D shapes come with parametric information for texture mapping purposes. In this paper we describe a spectral method to compress the geometric shapes equipped with arbitrary valid parametric information. It guarantees to preserve user-specified feature lines while achieving a high compression ratio. By applying the spectral shape analysis - Dirichlet Manifold Harmonics, in the 2D parametric domain, this method provides a progressive compression mechanism to trade-off between bit-rate and shape quality. Experiments show that this method provides very low bit-rate with high shape-quality and still guarantees the preservation of user-specified feature lines.
Alleviating the Modifiable Areal Unit Problem within Probe-Based Geospatial Analyses
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Butkiewicz, Thomas; Meentemeyer, Ross K.; Shoemaker, Douglas A.; Chang, Remco; Wartell, Zachary; Ribarsky, William; G. Melancon, T. Munzner, and D. Weiskopf
We present a probe-based interface for the exploration of the results of a geospatial simulation of urban growth. Because our interface allows the user great freedom in how they choose to define regions-of-interest to examine and compare, the classic geospatial analytic issue known as the modifiable areal unit problem (MAUP) quickly arises. The user may delineate regions with unseen differences that can affect the fairness of the comparisons made between them. To alleviate this problem, our interface first alerts the user if it detects any potential unfairness between regions when they are selected for comparison. It then presents the dimensions with potential problematic outliers to the user for evaluation. Finally, it provides a number of semi-automated tools to assist the user in correcting their regions boundaries to minimize the inequalities they feel could significantly impact their comparisons.
An Optimizing Compiler for Automatic Shader Bounding
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Clarberg, Petrik; Toth, Robert; Hasselgren, Jon; Akenine-Moeller, Tomas
Computational Aesthetics 2010 in London, England, June 14-15, 2010, sponsored by Eurographics, in collaboration with ACM SIGGRAPH
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Isenberg, Tobias; Dodgson, Neil
Sketching Clothoid Splines Using Shortest Paths
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Baran, Ilya; Lehtinen, Jaakko; Popovic, Jovan
Clothoid splines are gaining popularity as a curve representation due to their intrinsically pleasing curvature, which varies piecewise linearly over arc length. However, constructing them from hand-drawn strokes remains difficult. Building on recent results, we describe a novel algorithm for approximating a sketched stroke with a fair (i.e., visually pleasing) clothoid spline. Fairness depends on proper segmentation of the stroke into curve primitives - lines, arcs, and clothoids. Our main idea is to cast the segmentation as a shortest path problem on a carefully constructed weighted graph. The nodes in our graph correspond to a vastly overcomplete set of curve primitives that are fit to every subsegment of the sketch, and edges correspond to transitions of a specified degree of continuity between curve primitives. The shortest path in the graph corresponds to a desirable segmentation of the input curve. Once the segmentation is found, the primitives are fit to the curve using non-linear constrained optimization. We demonstrate that the curves produced by our method have good curvature profiles, while staying close to the user sketch.
Automatic Animation for Time-Varying Data Visualization
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Yu, Li; Lu, Aidong; Ribarsky, William; Chen, Wei
This paper presents a digital storytelling approach that generates automatic animations for time-varying data visualization. Our approach simulates the composition and transition of storytelling techniques and synthesizes animations to describe various event features. Specifically, we analyze information related to a given event and abstract it as an event graph, which represents data features as nodes and event relationships as links. This graph embeds a tree-like hierarchical structure which encodes data features at different scales. Next, narrative structures are built by exploring starting nodes and suitable search strategies in this graph. Different stages of narrative structures are considered in our automatic rendering parameter decision process to generate animations as digital stories. We integrate this animation generation approach into an interactive exploration process of time-varying data, so that more comprehensive information can be provided in a timely fashion. We demonstrate with a storm surge application that our approach allows semantic visualization of time-varying data and easy animation generation for users without special knowledge about the underlying visualization techniques.
Measuring Complexity in Lagrangian and Eulerian Flow Descriptions
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Jaenicke, H.; Scheuermann, G.
Automatic detection of relevant structures in scientific data sets is still one of the big challenges in visualization. Techniques based on information theory have shown to be a promising direction to automatically highlight interesting subsets of a time-dependent data set. The methods that have been proposed so far, however, were restricted to the Eulerian view. In the Eulerian description of motion, a position fixed in space is observed over time. In fluid dynamics, however, not only the site-specific analysis of the flow is of interest, but also the temporal evolution of particles that are advected through the domain by the flow. This second description of motion is called the Lagrangian perspective. To support these two different frames of reference widely used in CFD research, we extend the notion of local statistical complexity (LSC) to make them applicable to Lagrangian and Eulerian flow descriptions. Thus, coherent structures can be identified by highlighting positions that either feature unusual temporal dynamics at a fixed position or that hold a particle that experiences such dynamics while passing through the position. A new area of application is opened by LagrangianLSC, which can be applied to short pathlines running through each position in the data set, as well as to individual pathlines computed for longer time intervals. Coloring the pathline according to the local complexity helps to detect extraordinary dynamics while the particle passes through the domain. The two techniques are explained and compared using different fluid flow examples.
A New Ward BRDF Model with Bounded Albedo
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Geisler-Moroder, David; Duer, Arne
Due to its realistic appearance, computational convenience, and efficient Monte Carlo sampling, Ward s anisotropic BRDF is widely used in computer graphics for modeling specular reflection. Incorporating the criticism that the Ward and the Ward-Duer model do not meet energy balance at grazing angles, we propose a modified BRDF that is energy conserving and preserves Helmholtz reciprocity. The new BRDF is computationally cheap to evaluate, admits efficient importance sampling, and thus sustains the main benefits of the Ward model. We show that the proposed BRDF is better suited for fitting measured reflectance data of a linoleum floor used in a real-world building than the Ward and the Ward-Duer model.
A Salience-based Quality Metric for Visualization
(The Eurographics Association and Blackwell Publishing Ltd., 2010) Jänicke, Heike; Chen, Min; G. Melancon, T. Munzner, and D. Weiskopf
Salience detection is a principle mechanism to facilitate visual attention. A good visualization guides the observer s attention to the relevant aspects of the representation. Hence, the distribution of salience over a visualization image is an essential measure of the quality of the visualization. We describe a method for computing such a metric for a visualization image in the context of a given dataset. We show how this technique can be used to analyze a visualization s salience, improve an existing visualization, and choose the best representation from a set of alternatives. The usefulness of this proposed metric is illustrated using examples from information visualization, volume visualization and flow visualization.

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