Computer Graphics & Visual Computing (CGVC) 2014

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https://diglib.eg.org/handle/10.2312/7743

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Browsing Computer Graphics & Visual Computing (CGVC) 2014 by Title

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    Comparative Visualization and Analysis of Time-Dependent, 2D Foam Simulation Data
    (The Eurographics Association, 2014) Lipsa, Dan R.; Laramee, Robert S.; Cox, Simon; Davies, I. Tudur; Rita Borgo and Wen Tang
    Liquid foams have important practical applications. To analyze the dependence of foam behavior on material properties, and to improve foam models, foam scientists work with dozens of related simulations obtained by varying these material properties as well as parameters such as foam attributes, properties of objects interacting with foam or shape of foam containers. We present visualization solutions, developed in close collaboration with foam scientists, designed to compare and analyze related simulations.We evaluate our solutions by deploying them at the scientists' site. We demonstrate their effectiveness through results obtained by domain experts using our tool which include new findings and new approaches to analyze foam simulations. We propose a novel interaction and processing technique that enables the comparison of related events in different simulations and facilitates the examination of the temporal context for the events.
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    Fast and Simple Agglomerative LBVH Construction
    (The Eurographics Association, 2014) Apetrei, Ciprian; Rita Borgo and Wen Tang
    This paper continues the long-standing tradition of gradually improving the construction speed of spatial acceleration structures using sorted Morton codes. Previous work on this topic forms a clear sequence where each new paper sheds more light on the nature of the problem and improves the hierarchy generation phase in terms of performance, simplicity, parallelism and generality. Previous approaches constructed the tree by firstly generating the hierarchy and then calculating the bounding boxes of each node by using a bottom-up traversal. Continuing the work, we present an improvement by providing a bottom-up method that finds each node's parent while assigning bounding boxes, thus constructing the tree in linear time in a single kernel launch. Also, our method allows clustering the sorted points using an user-defined distance metric function.
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    Gap-Sensitive Segmentation and Restoration of Digital Images
    (The Eurographics Association, 2014) Sobiecki, Andre; Jalba, Andrei; Boda, Daniel; Diaconeasa, Adriana; Telea, Alexandru; Rita Borgo and Wen Tang
    Many methods exist for removing defects such as gaps, cracks, and disconnections from digital shapes. However, most such methods have several limitations, such as removing both erroneous and important shape details, or requiring non-trivial effort from the end user in the form of manual delineation or parameter setting. In this paper, we propose a technique for removing defects such as internal gaps and cracks from 2D and 3D digital shapes. For this, we first classify gaps as boundary detail (to be preserved) and interior errors (to be removed), based on a heuristic that uses the gap position with respect the medial axis of the simplified shape. Next, we remove error gaps using an efficient distance-based filling. We illustrate our method on robust segmentation and hair removal tasks for skin imaging, and compare our results with a number of relevant techniques in this area.
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    Geological Orientation Measurements using an iPad: Method Comparison
    (The Eurographics Association, 2014) Hama, Layik; Ruddle, Roy A.; Paton, Douglas; Rita Borgo and Wen Tang
    This paper describes a tablet-based application to be used by novice geologists for taking geological measurements during fieldwork. The application was implemented on an iPad2. Both our app and the FieldMove Clino iOS app (from Midland Valley, a well-known geophysics software company) were compared with ground truth measurements taken using a Silva compass clinometer. The results show that the dip angle measurements taken using the iPad2 device are accurate, but dip direction measurements not of acceptable accuracy. However, the results indicate that the iOS Core Location method could be combined with multiple measurements to provide acceptable accuracy.
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    Modelling of Clouds from a Hemispherical Image
    (The Eurographics Association, 2014) Alldieck, Thiemo; Lundtoft, Dennis H.; Montanari, Niels; Nikolov, Ivan; Vlaykov, Iskren G.; Madsen, Claus B.; Rita Borgo and Wen Tang
    This paper presents an image-based method for modelling clouds. Unlike previous image-based approaches, a hemispherical photograph is used as input, enabling to consider an entire sky instead of merely a portion. Our method computes the intensity and opacity of the clouds from the photograph. For this purpose, beforehand, the sun illumination is filtered, the pixels are classified between cloud and sky pixels, and the sky behind the clouds is reconstructed. After having been smoothed, the intensity of the clouds is used to create vertices on a hemisphere, and their radius coordinate is modulated by the intensity value of the corresponding pixel. Finally, the mesh is generated by triangulation of the vertices. Additionally, the use of the opacity of the clouds to simulate their transparency and render them is proposed. The results show that our method can be used to produce a realistic full sky populated with clouds in a very straightforward way for the user.
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    A Study on Glyph-based Visualisation with Dense Visual Context
    (The Eurographics Association, 2014) Khan, Saiful; Proctor, Karl J.; Walton, Simon; Bañares-Alcántara, René; Chen, Min; Rita Borgo and Wen Tang
    In a focus+context visualization, one often finds it difficult to overlay focus information on top of a dense visual context. This work is motivated by a need for visualizing search results (i.e., focus) in relation to a treemap representation of a large file system (i.e., context). We thus consider that the focus consists of a collection of visual objects discretely-distributed over a background featuring dense context information. The conventional approach for showing such objects in focus is to use colored dots, which can encode limited information and may be difficult to discern from the context background. In this paper, we report a study on three alternative approaches, namely (a) cyclically-animated dot, (b) static glyph and (c) cyclically-animated glyph. We conducted a focus group study for qualitative evaluation and found that cyclically-animated dots and static glyphs are the preferred alternatives. While fine tuning cyclic animation is feasible, cyclically-animated glyphs do not offer an attractive solution in general.
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    Variations on Image Reconstruction:Weighted Back Projection and Fourier Expectation Maximization
    (The Eurographics Association, 2014) Ryan, Andrew; Mora, B.; Rita Borgo and Wen Tang
    Expectation Maximization and Filtered Back Projection are two common techniques for Tomographic reconstruction of images and volumes. While papers often demonstrat that EM produces higher quality reconstructions, particularly from lower numbers of projections, FBP remains popular due to its low computational complexity. In the following work we present and analyse a modified Expectation Maximization approach which takes advantage of the Fourier Slice Theorem to reduce the bottleneck of forward and back projection. We also investigate Weighted Back Projection, a variation of Filtered Back Projection which uses a weighted average approach to avoid the use of arbitrarily chosen filters.
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    Visual Analysis of Hurricane Data Using Joint Contour Net
    (The Eurographics Association, 2014) Geng, Zhao; Duke, David; Carr, Hamish; Chattopadhyay, Amit; Rita Borgo and Wen Tang
    Topology provides a rigorous foundation for identifying features and transitions within data. However, computing and presenting topological features in multi-dimensional range space is still a difficult problem. The Joint Contour Net therefore is proposed as a data structure which quantizes the variation of multiple variables and presents multiple-field topology. In this paper, we apply the Joint Contour Net to real-world applications in order to present, analyse and explore features related to phenomenon. We have proposed a framework based on Joint Contour Net for iterative data exploration and knowledge discovery. The data set we investigate is from a simulation of Isabel Hurricane. We are able to demonstrate that the multi-field topological features such as rainbands, air flow and hurricane eye, as well as their relationship, can be exploited from a global topological view.