http://www.computer.org/tvcg The IEEE Transactions on Visualization and Computer Graphics (TVCG) is published bimonthly. Its Editorial Board strives to publish papers that present important research results and state-of-the-art seminal papers within TVCG's scope. These include subjects related to visualization and computer graphics techniques, systems, software, hardware, and user interface issues. Specific topics include, but are not limited to: a) visualization techniques and methodologies; b) visualization systems and software; c) volume visualization; d) flow visualization; e) information visualization; f) multivariate visualization; g) modeling and surfaces; h) rendering techniques and methodologies; i) graphics systems and software; j) animation and simulation; k) user interfaces; l) virtual reality; m) visual programming and program visualization; and n) applications. en-us Sun, 19 May 2013 10:00:07 GMT http://csdl.computer.org/common/images/logos/tvcg.gif List of recently published journal articles http://www.computer.org/tvcg http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.76 We present KelpFusion: a method for depicting set membership of items on a map or other visualization using continuous boundaries. KelpFusion is a hybrid representation that bridges hull techniques such as Bubble Sets and Euler Diagrams and line- and graph-based techniques such as LineSets and Kelp Diagrams. We describe an algorithm based on shortest-path graphs to compute KelpFusion visualizations. Based on a single parameter, the shortest-path graph varies from the minimal spanning tree to the convex hull of a point set. Shortest-path graphs aim to capture the shape of a point set and smoothly adapt to sets of varying densities. KelpFusion fills enclosed faces based on a set of simple legibility rules. We present the results of a controlled experiment comparing KelpFusion to Bubble Sets and LineSets. We conclude that KelpFusion outperforms Bubble Sets both in accuracy and completion time, and outperforms LineSets in completion time. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.76 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.65 We introduce Splatterplots, a novel presentation of scattered data that enables visualizations that scale beyond standard scatter plots. Traditional scatter plots suffer from overdraw (overlapping glyphs) as the number of points per unit area increases. Overdraw obscures outliers, hides data distributions, and makes the relationship among subgroups of the data difficult to discern. To address these issues, Splatterplots abstract away information such that the density of data shown in any unit of screen space is bounded, while allowing continuous zoom to reveal abstracted details. Abstraction automatically groups dense data points into contours and samples remaining points. We combine techniques for abstraction with with perceptually based color blending to reveal the relationship between data subgroups. The resulting visualizations represent the dense regions of each subgroup of the dataset as smooth closed shapes and show representative outliers explicitly. We present techniques that leverage the GPU for Splatterplot computation and rendering, enabling interaction with massive data sets. We show how splatterplots can be an effective alternative to traditional methods of displaying scatter data communicating data trends, outliers, and data set relationships much like traditional scatter plots, but scaling to data sets of higher density and up to millions of points on the screen. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.65 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.12 In this paper, we propose a novel framework for multi-domain subspace deformation using node-wise corotational elasticity. With the proper construction of subspaces based on the knowledge of the boundary deformation, we can use the Lagrange multiplier technique to impose coupling constraints at the boundary without over-constraining. In our deformation algorithm, the number of constraint equations to couple two neighboring domains is not related to the number of the nodes on the boundary but same to the number of the selected boundary deformation modes. The crack artifact is not present in our simulation result and the domain decomposition with loops can be easily handled. Experimental results show that the single core implementation of our algorithm can achieve real-time performance in simulating deformable objects with around quarter million tetrahedral elements. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.12 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.20 Scatterplots remain a powerful tool to visualize multi-dimensional data. However, accurately understanding the shape of multi-dimensional points from 2D projections remains challenging due to overlap. There are a lot of variations on the scatterplot as a visual metaphor for this limitation. An important aspect often overlooked in scatterplots is the issue of sensitivity or local trend, which may help in identifying the type of relationship between two variables. However, it is not well-known how or what factors influence the perception of trends from 2D scatterplots. We conducted an experiment where we asked people to directly draw the perceived trends on a 2D scatterplot. We found that augmenting scatterplots with local sensitivity helps to fill the gaps in visual perception while retaining the simplicity and readability of a 2D scatterplot. We call this augmentation the generalized sensitivity scatterplot. In a GSS, sensitivity coefficients are visually depicted as flow-lines, which gives a sense of continuity and orientation of the data that provide cues about the way data points are scattered in a higher dimensional space. We introduce a series of glyphs and operations that facilitate the analysis of multi-dimensional data sets using GSS, and validate with a number of well-known data sets for both regression and classification tasks. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.20 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.13 This paper shows that classifying shapes is a tool useful in Non-Photorealistic rendering from photographs. Our classifier inputs regions from an image segmentation hierarchy and outputs the ``best'' fitting simple shape such as a circle, square or triangle. Other approaches to NPR have recognised the benefits of segmentation, but none have classified the shape of segments. By doing so, we can create artwork of a more abstract nature, emulating the style of modern artists such as Matisse and other artists who favoured shape simplification in their artwork. The classifier chooses the shape that ``best'' represents the region. Since the classifier is trained by a user, the `best shape' has a subjective quality that can over-ride measurements such as minimum error and more importantly captures user preferences. Once trained, the system is fully automatic, although simple user interaction is also possible to allow for differences in individual tastes. A gallery of results shows how this classifier contributes to NPR from images by producing abstract artwork. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.13 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.11 Properly handling parallax is important for video stabilization. Existing methods that achieve the aim require either 3D reconstruction or long feature trajectories to enforce the subspace or epipolar geometry constraints. In this paper, we present a robust and efficient technique that works on general videos. It achieves high-quality camera motion on videos where 3D reconstruction is difficult or long feature trajectories are not available. We represent each trajectory as a Bezier curve and maintain the spatial relations between trajectories by preserving the original offsets of neighboring curves. Our technique formulates stabilization as a spatial-temporal optimization problem that finds smooth feature trajectories and avoids visual distortion. The Bezier representation enables strong smoothness of each feature trajectory and reduces the number of variables in the optimization problem. We also stabilize videos in a streaming fashion to achieve scalability. The experiments show that our technique achieves high-quality camera motion on a variety of challenging videos that are difficult for existing methods. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.11 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.7 In this paper, Cosine-Weighted B-spline (CWB) filters are proposed for interpolation on the optimal Body-Centered Cubic (BCC) lattice. We demonstrate that our CWB filters can well exploit the fast trilinear texture-fetching capability of modern GPUs, and outperform the state-of-the-art box-spline filters not just in terms of efficiency, but in terms of visual quality and numerical accuracy as well. Furthermore, we rigorously show that the CWB filters are better tailored to the BCC lattice than the previously proposed quasi-interpolating BCC B-spline filters, since they form a Riesz basis; exactly reproduce the original signal at the lattice points; but still provide the same approximation order. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.7 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.324 Investigators across many disciplines and organizations must sift through large collections of text documents to understand and piece together information. Whether they are fighting crime, curing diseases, deciding what car to buy, or researching a new field, inevitably investigators will encounter text documents. Taking a visual analytics approach, we integrate multiple text analysis algorithms with a suite of interactive visualizations in order to provide a flexible and powerful environment that allows analysts to explore collections of documents while sensemaking. Our particular focus is on the process of integrating automated analyses with interactive visualizations in a smooth and fluid manner. We illustrate this integration through two example scenarios: an academic researcher examining InfoVis and VAST conference papers and a consumer exploring car reviews while pondering a purchase decision. Finally, we provide lessons learned toward the design and implementation of visual analytics systems for document exploration and understanding. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.324 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.319 We propose '\emph{StereoPasting}', an efficient method for depth-consistent stereoscopic composition, in which a source 2D image is interactively blended into a target stereoscopic image. As we paint `disparity' on a 2D image, the disparity map of the selected region is gradually produced by edge-aware diffusion, and then blended with that of the target stereoscopic image. By considering constraints of the expected disparities and perspective scaling, the 2D object is warped to generate an image pair, which is then blended into the target image pair to get the composition result. The warping is formulated as an energy minimization, which could be solved in real time. We also present an interactive composition system, in which users can edit the disparity maps of 2D images by strokes, while viewing the composition results instantly. Experiments show that our method is intuitive and efficient for interactive stereoscopic composition. A lot of applications demonstrate the versatility of our method. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.319 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.317 As a controllable medium, video-realistic crowds are important for creating the illusion of a populated reality in special effects, games and architectural visualization. While recent progress in simulation and motion captured-based techniques for crowd synthesis has focused on natural macro-scale behavior, this paper addresses the complementary problem of synthesizing crowds with realistic micro-scale behavior and appearance. Example-based synthesis methods such as video textures are an appealing alternative to conventional model-based methods, but current techniques are unable to represent and satisfy constraints between video sprites and the scene. This paper describes how to synthesize crowds by segmenting pedestrians from input videos of natural crowds and optimally placing them into an output video while satisfying environmental constraints imposed by the scene. We introduce crowd tubes, a representation of video objects designed to compose a crowd of video billboards while avoiding collisions between static and dynamic obstacles. The approach consists of representing crowd tube samples and constraint violations with a conflict graph. The maximal independent set yields a dense constraint-satisyfing crowd composition. We present a prototype system for the capture, analysis, synthesis and control of video-based crowds. Several results demonstrate the system's ability to generate videos of crowds which exhibit a variety of natural behaviors. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.317 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.150 Streamline seeding rakes are widely used in vector field visualization. We present new approaches for calculating similarity between integral curves (streamlines and pathlines). While others have used similarity distance measures, the computational expense involved with existing techniques is shown to be high due to a vast number of Euclidean distance tests, restricting interactivity and their use for streamline seeding rakes. We introduce the novel idea of computing streamline signatures based on a set of attributes. A signature produces a compact representation for the description of a streamline. Similarity comparisons are performed by using a popular statistical measure on the created signatures. We demonstrate that this novel scheme produces good clustering results and is computed over 2 orders of magnitude faster than previous methods. Similarity-based clustering allows filtering of the streamlines to provide a non-uniform seeding distribution along the seeding object. We show that this method preserves the overall flow behavior while using only a small subset of the original streamline set. We also apply focus + context rendering using the clusters which allows for faster and easier analysis in cases of high visual complexity and occlusion. The method provides a high-level of interactivity and allows the user to easily fine-tune the clustering results at run-time while avoiding any time-consuming re-computation. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.150 http://opac.ieeecomputersociety.org/opac?year=2013&volume=10&issue=01&acronym=tvcg IEEE Transactions on Visualization and Computer Graphics http://www.computer.org/portal/site/tvcg/ http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.77 Given the growth of Internet photo collections we now have a visual index of all major cities and tourist sites in the world. However, it is still a difficult task to capture that perfect shot with your own camera when visiting these places, especially when your camera itself has limitations, such as a limited field of view. In this paper, we propose a framework to overcome the imperfections of personal photos of tourist sites using the rich information provided by large scale Internet photo collections. Our method deploys state-of-the-art techniques for constructing initial 3D models from photo collections. The same techniques are then used to register personal photos to these models, allowing us to augment personal 2D images with 3D information. This strong available scene prior allows us to address a number of traditionally challenging image enhancement techniques, and achieve high quality results using simple and robust algorithms. Specifically, we demonstrate automatic foreground segmentation, mono-to-stereo conversion, the field of view expansion, photometric enhancement, and additionally automatic annotation with geo-location and tags. Our method clearly demonstrates some possible benefits of employing the rich information contained in on-line photo databases to efficiently enhance and augment one’s own personal photos. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.77 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.75 A novel content-aware warping approach is introduced for video retargeting. The key to this technique is adapting videos to fit displays with various aspect ratios and sizes while preserving both visually salient content and temporal coherence. Most previous studies solve this spatiotemporal problem by consistently resizing content in frames. This strategy significantly improves the retargeting results, but does not fully consider object preservation, sometimes causing apparent distortions on visually salient objects. We propose an object-preserving warping scheme with object-based significance estimation to reduce this unpleasant distortion. In the proposed scheme, visually salient objects in 3D space-time space are forced to undergo as-rigid-as-possible warping, while low-significance objects are warped as close as possible to linear rescaling. These strategies enable our method to consistently preserve both the spatial shapes and temporal motions of visually salient objects, and avoid over-deformations on low-significance objects, yielding a pleasing motion-aware video retargeting. Qualitative analyses, including a user study with chi-squared test, and experiments on complex videos containing diverse cameras and dynamic motions, show a clear superiority of our method over state-of-the-art video retargeting methods. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.75 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.74 The huge number of points scanned from pipeline plants make the plant reconstruction very difficult. Traditional cylinder detection methods cannot be applied directly due to the high computational complexity. In this paper we explore the structural characteristics of point cloud in pipeline plants and define a structure feature. Based on the structure feature, we propose a hierarchical structure detection and decomposition method that reduces the difficult pipeline-plant reconstruction problem in R³ into a set of simple circle detection problems in R². Experiments with industrial applications are presented, which demonstrate the efficiency of the proposed structure detection method. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.74 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.73 The nonlinear and non-stationary nature of Navier-Stokes equations produces fluid flows that can be noticeably different in appearance with subtle changes. In this paper we introduce a method that can analyze the intrinsic multiscale features of flow fields from a decomposition point of view, by using the Hilbert-Huang transform method on 3D fluid simulation. We show how this method can provide insights to flow styles and help modulate the fluid simulation with its internal physical information. We provide easy-to-implement algorithms that can be integrated with standard grid-based fluid simulation methods, and demonstrate how this approach can modulate the flow field and guide the simulation with different flow styles. The modulation is straightforward and relates directly to the flow's visual effect, with moderate computational overhead. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.73 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.71 We present a novel, Linear Programming (LP) based scheduling algorithm that exploits heterogeneous multi-core architectures such as CPUs and GPUs to accelerate a wide variety of proximity queries. To represent complicated performance relationships between heterogeneous architectures and different computations of proximity queries, we propose a simple, yet accurate model that measures the expected running time of these computations. Based on this model, we formulate an optimization problem that minimizes the largest time spent on computing resources, and propose a novel, iterative LP-based scheduling algorithm. Since our method is general, we are able to apply our method into various proximity queries that have different characteristics. Our method achieves an order of magnitude performance improvement by using four different GPUs and two hexa-core CPUs over using a hexa-core CPU only. Unlike prior scheduling methods, our method continually improves the performance, as we add more computing resources. Also, our method achieves much higher performance improvement compared with prior methods as heterogeneity of computing resources is increased. We also show that our method provides results that are close to the performance provided by a conservative upper bound of the ideal throughput. These results demonstrate the efficiency and robustness of our algorithm that have not been achieved by prior methods. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.71 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.72 The k-buffer algorithm is an efficient GPU based fragment level sorting algorithm for rendering transparent surfaces. Because of the inherent massive parallelism of GPU stream processors, this algorithm suffers serious read-after-write memory hazards now. In this paper, we introduce an improved k-buffer algorithm with error correction coding to combat memory hazards. Our algorithm results in significantly reduced artifacts. While preserving all the merits of the original algorithm, it requires merely OpenGL 3.x support from the GPU, instead of the atomic operations appearing only in the latest OpenGL 4.2 standard. Our algorithm is simple to implement and efficient in performance. Future GPU support for improving this algorithm is also proposed. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.72 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.68 In this paper, we propose an unwrappable representation for image-based facade modeling from multiple registered images. An unwrappable facade is represented by the mutually orthogonal baseline and profile. We first reconstruct semi-dense 3D points from images, then the baseline and profile are extracted from the point cloud to construct the base shape and compose the textures of the building from the images. Through our unwrapping process, the reconstructed 3D points and composed textures are further mapped to an unwrapped space that is parameterized by the baseline and profile. In doing so, the unwrapped space becomes equivalent to the planar space in which planar facade modeling techniques can be used to reconstruct the details of the buildings. Finally, the augmented details can be wrapped back to the original 3D space to generate the final model. This newly introduced unwrappable representation extends the state of the art modeling for planar facades to a more general class of facades. We demonstrate the power of the unwrappable representation with a few examples in which the facade is not planar. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.68 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.67 Virtual try-on applications have become popular because they allow users to watch themselves wearing different clothes without the effort of changing them physically. This helps users to make quick buying decisions and thus improves the sales efficiency of retailers. Previous solutions usually involve motion capture, 3D reconstruction or modeling, which are time consuming and not robust for all body poses. Our method avoids these steps by combining image-based renderings of the user and previously recorded garments. It transfers the appearance of a garment recorded from one user to another by matching input and recorded frames, image-based visual hull rendering and online registration methods. Using images of real garments allows for a realistic rendering quality with high performance. It is suitable for a wide range of clothes and complex appearances, allows arbitrary viewing angles and requires only little manual input. Our system is particularly useful for virtual try-on applications as well as interactive games. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.67 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.66 We present Bristle Map, a novel method for the aggregation and abstraction of spatiotemporal data that enables multi-attribute visualization, exploration, and analysis. This visualization technique supports the display of multidimensional data by providing users with a multi-parameter encoding scheme within a single visual encoding paradigm. Given a set of spatiotemporal events, we compute density estimation that encodes the probability that an event will occur within the space over a given temporal aggregation. These probability values are then encoded into a bristle map. A bristle map consists of a series of straight lines that extend from linear map elements. These lines vary in length, density, color, and orientation and transparency—creating the multivariate encoding scheme where event magnitude and change can be mapped as various bristle parameters. This approach increases the amount of information displayed in a single plot. We demonstrate the use of our bristle map using categorical spatiotemporal police reports for visualizing data magnitude, variable comparisons, and various multivariate attribute combinations. To evaluate the effectiveness, we have conducted quantitative and qualitative evaluations where we compare our bristle map to conventional geovisualization techniques. Our results show that bristle maps are competitive in time and accuracy of tasks with various levels of complexity. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.66 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.63 Poisson disk sampling plays an important role in a variety of visual computing, due to its useful statistical property in distribution and the absence of aliasing artifacts. While many effective techniques have been proposed to generate Poisson disk distribution in Euclidean space, relatively few work has been reported to the surface counterpart. This paper presents an intrinsic algorithm for parallel Poisson disk sampling on arbitrary surfaces. We propose a new technique for parallelizing the dart throwing. Rather than the conventional approaches that explicitly partition the spatial domain to generate the samples in parallel, our approach assigns each sample candidate a random and unique priority that is unbiased with regard to the distribution. Hence, multiple threads can process the candidates simultaneously and resolve conflicts by checking the given priority values. It is worth noting that our algorithm is accurate as the generated Poisson disks are uniformly and randomly distributed without bias. Our method is intrinsic in that all the computations are based on the intrinsic metric and are independent of the embedding space. This intrinsic feature allows us to generate Poisson disk distributions on arbitrary surfaces. Furthermore, by manipulating the spatially varying density function, we can obtain adaptive sampling easily. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.63 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.21 This paper proposes the VisibilityCluster algorithm for efficient visibility approximation and representation in many-light rendering. By carefully clustering lights and shading points, we can construct a visibility matrix that exhibits good local structures due to visibility coherence of nearby lights and shading points. Average visibility can be efficiently estimated by exploiting the sparse structure of the matrix and shooting only few shadow rays between clusters. Moreover, we can use the estimated average visibility as a quality measure for visibility estimation, enabling us to locally refine VisibilityClusters with large visibility variance for improving accuracy. We demonstrate that, with the proposed method, visibility can be incorporated into importance sampling at a reasonable cost for the many-light problem, significantly reducing variance in Monte Carlo rendering. In addition, the proposed method can be used to increase realism of local shading by adding directional occlusion effects. Experiments show that the proposed technique outperforms state-of-the-art importance sampling algorithms, and successfully enhances the preview quality for lighting design. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.21 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.44 Hardware tessellation is one of the latest GPU features. Triangle or quad meshes are tessellated on-the-fly, where the tessellation level is chosen adaptively in a separate shader. The hardware tessellator only generates topology; attributes such as positions or texture coordinates of the newly generated vertices are determined in a domain shader. Typical applications of hardware tessellation are view dependent tessellation of parametric surfaces and displacement mapping. Often, the attributes for the newly generated vertices are stored in textures, which requires uv unwrapping, chartification, and atlas generation of the input mesh - a process that is time consuming and often requires manual intervention. In this paper, we present an alternative representation that directly stores optimized attribute values for typical hardware tessellation patterns and simply assigns these attributes to the generated vertices at render time. Using a multi-level fitting approach, the attribute values are optimized for several resolutions. Thereby, we require no parameterization, save memory by adapting the density of the samples to the content, and avoid discontinuities by construction. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.44 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.22 Many algorithms have been proposed for the task of efficient compression of triangular meshes. Geometric properties of the input data are usually exploited to obtain an accurate prediction of the data at the decoder. Considerations on how to improve the prediction usually focus on its normal part, assuming that the tangential part behaves similarly. In this paper, we show that knowledge of vertex valences might allow the decoder to form a prediction that is more accurate in the tangential direction, using a weighted parallelogram prediction. This idea can be easily implemented into existing compression algorithms, such as Edgebreaker, and it can be applied at different levels of sophistication, from very simple ones, that are computationally very cheap, to some more complex ones that provide an even better compression efficiency. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.22 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.18 Characterizing the interplay between the vortices and forces acting on a wind turbine's blades in a qualitative and quantitative way holds the potential for significantly improving large wind turbine design. The paper introduces an integrated pipeline for highly effective wind and force field analysis and visualization. We extract vortices induced by a turbine's rotation in a wind field, and characterize vortices in conjunction with numerically simulated forces on the blade surfaces as these vortices strike another turbine's blades downstream. The scientifically relevant issue to be studied is the relationship between the extracted, approximate locations on the blades where vortices strike the blades and the forces that exist in those locations. This integrated approach is used to detect and analyze turbulent flow that causes local impact on the wind turbine blade structure. The results that we present are based on analyzing the wind and force field data sets generated by numerical simulations, and allow domain scientists to relate vortex-blade interactions with power output loss in turbines and turbine life-expectancy. Our methods have the potential to improve turbine design in order to save costs related to turbine operation and maintenance. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.18 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.10 Most professional wind visualizations show wind speed and direction using a glyph called a wind barb in a grid pattern. Research into flow visualization has suggested that streamlines better represent flow patterns but these methods lack a key property—unlike the wind barb they do not accurately convey the wind speed. With the goal of improving the perception of wind patterns, and at least equaling the quantitative quality of wind barbs, we designed two variations on the wind barb and designed a new quantitative glyph. All of our new designs space glyph elements along equally spaced streamlines. To evaluate these designs we used a North American mesoscale forecast model. We tested the ability of subjects to determine direction and speed using two different densities each of three new designs as well as the classic wind barb. A second experiment evaluated how effectively each of the designs represented wind patterns. The results showed that the new design is superior to the classic, but they also showed that the classic barb can be re-designed and substantially improved. We suggest that flow patterns with integrated glyphs may have widespread application in flow visualization. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.10 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.8 This paper presents a simple, three stage method to simulate the mechanics of wetting of porous solid objects, like sponges and cloth, when they interact with a fluid. In the first stage, we model the absorption of fluid by the object when it comes in contact with the fluid. In the second stage, we model the transport of absorbed fluid inside the object, due to diffusion, as a flow in a deforming, unstructured mesh. The fluid diffuses within the object depending on saturation of its various parts and other body forces. Finally, in the third stage, over-saturated parts of the object shed extra fluid by dripping. The simulation model is motivated by the physics of imbibition of fluids into porous solids in the presence of gravity. It is phenomenologically capable of simulating wicking and imbibition, dripping, surface flows over wet media, material weakening and volume expansion due to wetting. The model is inherently mass conserving and works for both thin 2D objects like cloth and for 3D volumetric objects like sponges. It is also designed to be computationally efficient and can be easily added to existing cloth, soft body and fluid simulation pipelines. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.8 http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.9 We present a method for computing "choking" loops—a set of surface loops that describe the narrowing of the volumes inside/outside of the surface and extend the notion of surface homology and homotopy loops. The intuition behind their definition is that a choking loop represents the region where an offset of the original surface would get pinched. Our generalized loops naturally include the usual 2g handles/tunnels computed based on the topology of the genus-g surface, but also include loops that identify chokepoints or bottlenecks, i.e., boundaries of small membranes separating the inside or outside volume of the surface into disconnected regions. Our definition is based on persistent homology theory, which gives a measure to topological structures, thus providing resilience to noise and a well-defined way to determine topological feature size. More precisely, the persistence computed here is based on the lower star filtration of the interior or exterior 3D domain with the distance field to the surface being the associated 3D Morse function. http://doi.ieeecomputersociety.org/10.1109/TVCG.2013.9 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.325 This paper presents the first method for full-body trajectory optimization of physics-based human motion that does not rely on motion capture, specified key-poses, or periodic motion. Optimization is performed using a small set of simple goals, e.g., one hand should be on the ground or the center-of-mass should be above a particular height. These objectives are applied to short spacetime windows which can be composed to express goals over an entire animation. Specific contact locations needed to achieve objectives are not required by our method. We show that the method can synthesize many different kinds of movement, including walking, hand walking, breakdancing, flips, and crawling. Most of these movements have never been previously synthesized by physics-based methods. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.325 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.320 Rendering multi-fragment effects using GPUs is attractive for high speed. However, the efficiency is seriously compromised, because ordering fragments on GPUs is not easy and the GPU's memory may not be large enough to store the whole scene geometry. Hitherto, existing methods have been unsuitable for large models or have required many passes for data transmission from CPU to GPU, resulting in a bottleneck for speedup. This paper presents a stream method for accurate rendering of multi-fragment effects. It decomposes the model into parts and manages these in an efficient manner, guaranteeing that the parts can easily be ordered with respect to any viewpoint, and that each part can be rendered correctly on the GPU. Thus, we can transmit the model data part by part, and once a part has been loaded onto the GPU we immediately render it and composite its result with the results of the processed parts. In this way, we need only a single pass for data access with a very low bounded memory requirement. Moreover, we treat parts in packs for further acceleration. Results show that our method is much faster than existing methods, and can easily handle large models of any size. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.320 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.323 Many 2D visual spaces have a virtually one-dimensional nature with very high aspect ratio between the dimensions: examples include time-series data, multimedia data such as sound or video, text documents, and bipartite graphs. Common among these is that the space can become very large, e.g., temperature measurements could span a long time period, surveillance video could cover entire days or weeks, and documents can have thousands of pages. Many analysis tasks for such spaces require several foci while retaining context and distance awareness. In this extended version of our IEEE PacificVis 2010 paper, we introduce a method for supporting this kind of multi-focus interaction that we call stack zooming. The approach is based on building hierarchies of 1D strips stacked on top of each other, where each subsequent stack represents a higher zoom level, and sibling strips represent branches in the exploration. Correlation graphics show the relation between stacks and strips of different levels, providing context and distance awareness for the foci. The zoom hierarchies can also be used as graphical histories and for communicating insights to stakeholders, and can be further extended with annotation and integrated statistics. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.323 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.321 This paper presents a new label layout technique for projection-based augmented reality (AR) that determines the placement of each label directly projected onto an associated physical object with a surface that is normally inappropriate for projection (i.e., non-planar and textured). Central to our technique is a new legibility estimation method that evaluates how easily people can read projected characters from arbitrary viewpoints. The estimation method relies on the results of a psychophysical study that we conducted to investigate the legibility of projected characters on various types of surfaces that deform their shapes, decrease their contrasts, or cast shadows on them. Our technique computes a label layout by minimizing the energy function using a genetic algorithm (GA). The terms in the function quantitatively evaluate different aspects of the layout quality. Conventional label layout solvers evaluate anchor regions and leader lines. In addition to these evaluations, we design our energy function to deal with the following unique factors, which are inherent in projection-based AR applications: the estimated legibility value and the disconnection of the projected leader line. The results of our subjective experiment showed that the proposed technique could significantly improve the projected label layout. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.321 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.304 The paper is devoted to the derivation of a bidirectional distribution function for crystals, which specifies all outgoing rays for a ray coming to the boundary of two transparent crystalline media with different optical properties, i.e., a particular mineral, directions of optical axes if they exist, and other features. A local model of interaction based on the notion of polarized light ray is introduced, which is specified by a geometric ray, its polarization state, light intensity, etc. The computational algorithm that is suggested allows computing the directions and other properties of all (up to four) outgoing rays. In this paper, isotropic, uniaxial, and biaxial crystals are processed in a similar manner. The correctness of the model is validated by comparison of photos of real uniaxial crystals with corresponding computed images. The case of biaxial crystals is validated by testing the effect of conical refraction. Specifications of a series of tests devoted to rendering of optically different objects is presented also. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.304 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.315 Visualization techniques often use color to present categorical differences to a user. The selection of a color palette needs careful considerations of perceptual qualities of color. Large coherent groups visually suppress smaller groups, and thus, are often visually dominant in images. This article introduces the concept of class visibility to quantitatively measure the utility of a color palette to present coherent categorical structure to the user. We present a color optimization algorithm based on our class visibility metric to make categorical differences clearly visible to the user. We performed two user experiments, a user preference and visual search experiment, to validate our visibility measure over a range of color palettes. The results indicate that visibility is a robust measure, and our color optimization can increase the effectiveness of categorical data visualizations. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.315 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.303 This paper presents a novel approach to simulating turbulent flows by developing an adaptive multi-relaxation scheme in the framework of lattice Boltzmann equation (LBE). Existing LBE methods in graphics simulations are usually insufficient for turbulent flows since the collision term disturbs the underlying stability and accuracy. We adopt LBE with the multiple relaxation time (MRT) collision model (MRT-LBE), and address this issue by enhancing the collision-term modeling. First, we employ renormalization group analysis and formulate a new turbulence model with an adaptive correction method to compute more appropriate eddy viscosities on a uniform lattice structure. Efficient algebraic calculations are retained with small-scale turbulence details while maintaining the system stability. Second, we note that for MRT-LBE, predicting single eddy viscosity per lattice node may still result in instability. Hence, we simultaneously predict multiple eddy viscosities for stress-tensor-related elements, thereby asynchronously computing multiple relaxation parameters to further enhance the MRT-LBE stability. With these two new strategies, turbulent flows can be simulated with finer visual details even on coarse grid configurations. We demonstrate our results by simulating and visualizing various turbulent flows, particularly with smoke animations, where stable turbulent flows with high Reynolds numbers can be faithfully produced. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.303 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.176 Video synopsis aims at providing condensed representations of video datasets that can be easily captured from digital cameras nowadays, especially for daily surveillance videos. Previous work in video synopsis usually moves active objects along the time axis, which inevitably causes collisions among the moving objects if compressed much. In this paper, we propose a novel approach for compact video synopsis using a unified spatiotemporal optimization. Our approach globally shifts moving objects in both spatial and temporal domains, which shifting objects temporally to reduce the length of the video and shifting colliding objects spatially to avoid visible collision artifacts. Furthermore, using a multi-level patch relocation method, the moving space of the original video is expanded into a compact background based on environmental content to fit with the shifted objects. The shifted objects are finally composited with the expanded moving space to obtain the high-quality video synopsis, which is more condensed while remaining free of collision artifacts. Our experimental results have shown that the compact video synopsis we produced can be browsed quickly, preserves relative spatiotemporal relationships, and avoids motion collisions. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.176 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.177 This paper develops a novel volumetric parameterization and spline construction framework, which is an effective modeling tool for converting surface meshes to volumetric splines. Our new splines are defined upon a novel parametric domain called generalized poly-cubes (GPCs). A GPC comprises a set of regular cube domains topologically glued together. Compared with conventional poly-cubes (CPCs), GPC is much more powerful and flexible and has improved numerical accuracy and computational efficiency when serving as a parametric domain. We design an automatic algorithm to construct the GPC domain while also permitting the user to improve shape abstraction via interactive intervention. We then parameterize the input model on the GPC domain. Finally, we devise a new volumetric spline scheme based on this seamless volumetric parameterization. With a hierarchical fitting scheme, the proposed splines can fit data accurately using reduced number of superfluous control points. Our volumetric modeling scheme has great potential in shape modeling, engineering analysis, and reverse engineering applications. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.177 http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.151 We present a novel approach for GPU-based high quality volume rendering of large out-of-core volume data. By focusing on the locations and costs of ray traversal, we are able to significantly reduce the rendering time over traditional algorithms. We store a volume in an octree (of bricks); in addition, every brick is further split into regular macro-cells. Our solutions move the branch-intensive accelerating structure traversal out of the GPU raycasting loop and introduce an efficient empty-space culling method by rasterizing the proxy geometry of a view-dependent cut of the octree nodes. This rasterization pass can capture all of the bricks that the ray penetrates in a per-pixel list. Since the per-pixel list is captured in a front-to-back order, our raycasting pass needs only to cast rays inside the tighter ray segments. As a result, we achieve two levels of empty space skipping: the brick level and the macro-cell level. During evaluation and testing, this technique achieved 2 to 4 times faster rendering speed than a current state-of-the-art algorithm across a variety of data sets. http://doi.ieeecomputersociety.org/10.1109/TVCG.2012.151