33-Issue 8

Permanent URI for this collection

https://diglib.eg.org/handle/10.2312/11790

Browse

Now showing 1 - 17 of 17

Structural Analysis of Multivariate Point Clouds Using Simplicial Chains
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Rieck, B.; Leitte, H.; Oliver Deussen and Hao (Richard) Zhang
Topological and geometrical methods constitute common tools for the analysis of high‐dimensional scientific data sets. Geometrical methods such as projection algorithms focus on preserving distances in the data set. Topological methods such as contour trees, by contrast, focus on preserving structural and connectivity information. By combining both types of methods, we want to benefit from their individual advantages. To this end, we describe an algorithm that uses persistent homology to analyse the topology of a data set. Persistent homology identifies high‐dimensional holes in data sets, describing them as simplicial chains. We localize these chains using geometrical information of the data set, which we obtain from geodesic distances on a neighbourhood graph. The localized chains describe the structure of point clouds. We represent them using an interactive graph, in which each node describes a single chain and its geometrical properties. This graph yields a more intuitive understanding of multivariate point clouds and simplifies comparisons of time‐varying data. Our method focuses on detecting and analysing inhomogeneous regions, i.e. holes, in a data set because these regions characterize data in a different manner, thereby leading to new insights. We demonstrate the potential of our method on data sets from particle physics, political science and meteorology.We present simplicial chain graphs, a new visual metaphor for the analysis of multivariate point clouds. Our method first calculates the persistent homology of a data set. We represent topological features as simplicial chains, which we localize using geometrical information about the data set. We then display the simplicial chains and their relations in an interactive graph that serves as a concise structural description of multivariate point clouds.
Optimized Generation of Stereoscopic CGI Films by 3D Image Warping
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Noguera, José M.; Rueda, Antonio J.; Espada, Miguel A.; Martín, Máximo; Oliver Deussen and Hao (Richard) Zhang
The generation of a stereoscopic animation film requires doubling the rendering times and hence the cost. In this paper, we address this problem and propose an automatic system for generating a stereo pair from a given image and its depth map. Although several solutions exist in the literature, the high standards of image quality required in the context of a professional animation studio forced us to develop specially crafted algorithms that avoid artefacts caused by occlusions, anti‐aliasing filters, etc. This paper describes all the algorithms involved in our system and provides their GPU implementation. The proposed system has been tested with real‐life working scenarios. Our experiments show that the second view of the stereoscopic pair can be computed with as little as 15% of the effort of the original image while guaranteeing a similar quality.The generation of a stereoscopic animation film requires doubling the rendering times and hence the cost. In this paper, we address this problem and propose an automatic system for generating a stereo pair from a given image and its depth map. Although several solutions exist in the literature, the high standards of image quality required in the context of a professional animation studio forced us to develop specially crafted algorithms that avoid artefacts caused by occlusions, anti‐aliasing filters, etc.
Real-Time Modelling of Fibrous Muscle
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Kohout, J.; Kukacka, M.; Oliver Deussen and Hao (Richard) Zhang
Relatively recently it has become apparent that providing human kind with a better healthcare requires personalized, predictive and integrative medicine, for which the building of virtual physiological human (VPH) framework accessible via virtual patient avatar is necessary. Real-time modelling and visual exploration of such a complex avatar is a challenging task. In this paper, we propose a real-time method for automatic modelling of an arbitrarily large number of muscle fibres in the volume of a muscle represented by its surface mesh. The method is based on an iterative morphing of predefined fibres template into the muscle volume exploiting harmonic scalar field computed on the surface of muscle. Experiments with muscles of thighs and pelvis show that the method produces realistic shapes of fibres. Our sequential VTK-based C++ implementation is capable of producing 64 fine fibres within a muscle of 10K triangles in less than 170 ms on commodity hardware making the method suitable for VPH purposes as well as for interactive educational medical software.Relatively recently it has become apparent that providing human kind with a better healthcare requires personalised, predictive and integrative medicine, for which the building of Virtual Physiological Human (VPH) framework accessible via virtual patient avatar is necessary. Real-time modelling and visual exploration of such a complex avatar is a challenging task. In this paper, we propose a real-time method for automatic modeling of an arbitrarily large number of muscle fibres in the volume of a muscle represented by its surface mesh. The method is based on an iterative morphing of predefined fibres template into the muscle volume exploiting harmonic scalar field computed on the surface of muscle.
Variational Tree Synthesis
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Wang, Rui; Yang, Yinhui; Zhang, Hongxin; Bao, Hujun; Oliver Deussen and Hao (Richard) Zhang
Modelling trees according to desired shapes is important for many applications. Despite numerous methods having been proposed in tree modelling, it is still a non‐trivial task and challenging. In this paper, we present a new variational computing approach for generating realistic trees in specific shapes. Instead of directly modelling trees from symbolic rules, we formulate the tree modelling as an optimization process, in which a variational cost function is iteratively minimized. This cost function measures the difference between the guidance shape and the target tree crown. In addition, to faithfully capture the branch structure of trees, several botanical factors, including the minimum total branches volume and spatial branches patterns, are considered in the optimization to guide the tree modelling process. We demonstrate that our approach is applicable to generate trees with different shapes, from interactive design and complex polygonal meshes.Modeling trees according to desired shapes is important for many applications. Despite numerous methods having been proposed in tree modeling, it is still a non‐trivial task and challenging. In this paper, we present a new variational computing approach for generating realistic trees in specific shapes. Instead of directly modeling trees from symbolic rules, we formulate the tree modeling as an optimization process, in which a variational cost function is iteratively minimized. This cost function measures the difference between the guidance shape and the target tree crown.
Object Repositioning Based on the Perspective in a Single Image
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Iizuka, S.; Endo, Y.; Hirose, M.; Kanamori, Y.; Mitani, J.; Fukui, Y.; Oliver Deussen and Hao (Richard) Zhang
We propose an image editing system for repositioning objects in a single image based on the perspective of the scene. In our system, an input image is transformed into a layer structure that is composed of object layers and a background layer, and then the scene depth is computed from the ground region that is specified by the user using a simple boundary line. The object size and order of overlapping are automatically determined during the reposition based on the scene depth. In addition, our system enables the user to move shadows along with objects naturally by extracting the shadow mattes using only a few user‐specified scribbles. Finally, we demonstrate the versatility of our system through applications to depth‐of‐field effects, fog synthesis and 3D walkthrough in an image.We propose an image editing system for repositioning objects in a single image based on the perspective of the scene. In our system, an input image is transformed into a layer structure that is composed of object layers and a background layer, and then the scene depth is computed from the ground region that is specified by the user using a simple boundary line. The object size and order of overlapping are automatically determined during the reposition based on the scene depth. In addition, our system enables the user to move shadows along with objects naturally by extracting the shadow mattes using only a few user‐specified scribbles.
The PAG Crowd: A Graph Based Approach for Efficient Data‐Driven Crowd Simulation
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Charalambous, P.; Chrysanthou, Y.; Oliver Deussen and Hao (Richard) Zhang
We present a data‐driven method for the real‐time synthesis of believable steering behaviours for virtual crowds. The proposed method interlinks the input examples into a structure we call the perception‐action graph (PAG) which can be used at run‐time to efficiently synthesize believable virtual crowds. A virtual character's state is encoded using a temporal representation, the Temporal Perception Pattern (TPP). The graph nodes store groups of similar TPPs whereas edges connecting the nodes store actions (trajectories) that were partially responsible for the transformation between the TPPs. The proposed method is being tested on various scenarios using different input data and compared against a nearest neighbours approach which is commonly employed in other data‐driven crowd simulation systems. The results show up to an order of magnitude speed‐up with similar or better simulation quality.We present a data‐driven method for the real‐time synthesis of believable steering behaviours for virtual crowds. The proposed method interlinks the input examples into a structure we call the perception‐action graph (PAG) which can be used at run‐time to efficiently synthesize believable virtual crowds. A virtual character's state is encoded using a temporal representation, the temporal perception pattern (TPP). The graph nodes store groups of similar TPPs whereas edges connecting the nodes store actions (trajectories) that were partially responsible for the transformation between the TPPs.
Adaptive Surface Visualization of Vessels with Animated Blood Flow
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Lawonn, Kai; Gasteiger, Rocco; Preim, Bernhard; Oliver Deussen and Hao (Richard) Zhang
The investigation of hemodynamic information for the assessment of cardiovascular diseases (CVDs) gained importance in recent years. Improved flow measuring modalities and computational fluid dynamics (CFD) simulations yield in reliable blood flow information. For a visual exploration of the flow information, domain experts are used to investigate the flow information combined with its enclosed vessel anatomy. Since the flow is spatially embedded in the surrounding vessel surface, occlusion problems have to be resolved. A visual reduction of the vessel surface that still provides important anatomical features is required. We accomplish this by applying an adaptive surface visualization inspired by the suggestive contour measure. Furthermore, an illustration is employed to highlight the animated pathlines and to emphasize nearby surface regions. Our approach combines several visualization techniques to improve the perception of surface shape and depth. Thereby, we ensure appropriate visibility of the embedded flow information, which can be depicted with established or advanced flow visualization techniques. We apply our approach to cerebral aneurysms and aortas with simulated and measured blood flow. An informal user feedback with nine domain experts, we confirm the advantages of our approach compared with existing methods, e.g. semi‐transparent surface rendering. Additionally, we assessed the applicability and usefulness of the pathline animation with highlighting nearby surface regions.The investigation of hemodynamic information for the assessment of cardiovascular diseases (CVD) gained importance in recent years. Improved flow measuring modalities and computational fluid dynamics (CFD) simulations yield in reliable blood flow information. For a visual exploration of the flow information, domain experts are use to investigate the flow information combined with its enclosed vessel anatomy. Since the flow is spatially embedded in the surrounding vessel surface, occlusion problems have to be resolved. A visual reduction of the vessel surface that still provides important anatomical features is required. We accomplish this by applying an adaptive surface visualization inspired by the suggestive contour measure.
Managing Spatial Selections With Contextual Snapshots
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Mindek, P.; Gröller, M. E.; Bruckner, S.; Oliver Deussen and Hao (Richard) Zhang
Spatial selections are a ubiquitous concept in visualization. By localizing particular features, they can be analysed and compared in different views. However, the semantics of such selections often depend on specific parameter settings and it can be difficult to reconstruct them without additional information. In this paper, we present the concept of contextual snapshots as an effective means for managing spatial selections in visualized data. The selections are automatically associated with the context in which they have been created. Contextual snapshots can also be used as the basis for interactive integrated and linked views, which enable in‐place investigation and comparison of multiple visual representations of data. Our approach is implemented as a flexible toolkit with well‐defined interfaces for integration into existing systems. We demonstrate the power and generality of our techniques by applying them to several distinct scenarios such as the visualization of simulation data, the analysis of historical documents and the display of anatomical data.Spatial selections are a ubiquitous concept in visualization. By localizing particular features, they can be analyzed and compared in different views. However, the semantics of such selections often depend on specific parameter settings and it can be difficult to reconstruct them without additional information. In this paper, we present the concept of contextual snapshots as an effective means for managing spatial selections in visualized data. The selections are automatically associated with the context in which they have been created. Contextual snapshots can also be used as the basis for interactive integrated and linked views, which enable in‐place investigation and comparison of multiple visual representations of data.
Exemplar‐Based Portrait Photograph Enhancement as Informed by Portrait Paintings
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Zhang, Xiaoyan; Constable, Martin; Chan, Kap Luk; Oliver Deussen and Hao (Richard) Zhang
This paper proposes an approach to enhance the regional contrasts in snap‐shot style portrait photographs by using pre‐modern portrait paintings as aesthetic exemplars. The example portrait painting is selected based on a comparison of the existing contrast properties of the painting with those of the photograph. The contrast organization in the selected example painting is transferred to the photograph by mapping the inter‐ and intra‐regional contrasts of the regions, such as the face and skin areas of the foreground figure, the non‐face/skin part of the foreground and the background region. A piecewise non‐linear transformation curve is used to achieve the contrast mapping. Finally, the transition boundary between regions is smoothed to achieve the final results. The experimental results and user study demonstrate that, by using this proposed approach, the visual appeal of the portrait photographs is effectively improved, and the face and the figure become more salient.This paper proposes an approach to enhance the regional contrasts in snap‐shot style portrait photographs by using pre‐modern portrait paintings as aesthetic exemplars. The example portrait painting is selected based on a comparison of the existing contrast properties of the painting with those of the photograph. The contrast organization in the selected example painting is transferred to the photograph by mapping the inter‐ and intra‐regional contrasts of the regions, such as the face and skin areas of the foreground figure, the non‐face/skin part of the foreground, and the background region. A piecewise nonlinear transformation curve is used to achieve the contrast mapping.
Reviewers
(The Eurographics Association and Blackwell Publishing Ltd., 2014) Holly Rushmeier and Oliver Deussen
A Projective Framework for Polyhedral Mesh Modelling
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Vaxman, Amir; Oliver Deussen and Hao (Richard) Zhang
We present a novel framework for polyhedral mesh editing with face‐based projective maps that preserves planarity by definition. Such meshes are essential in the field of architectural design and rationalization. By using homogeneous coordinates to describe vertices, we can parametrize the entire shape space of planar‐preserving deformations with bilinear equations. The generality of this space allows for polyhedral geometric processing methods to be conducted with ease. We demonstrate its usefulness in planar‐quadrilateral mesh subdivision, a resulting multi‐resolution editing algorithm, and novel shape‐space exploration with prescribed transformations. Furthermore, we show that our shape space is a discretization of a continuous space of conjugate‐preserving projective transformation fields on surfaces. Our shape space directly addresses planar‐quad meshes, on which we put a focus, and we further show that our framework naturally extends to meshes with faces of more than four vertices as well.We present a novel framework for polyhedral mesh editing with face‐based projective maps, that preserves planarity by definition. Such meshes are essential in the field of architectural design and rationalization. By using homogeneous coordinates to describe vertices, we can parametrize the entire shape space of planar‐preserving deformations with bilinear equations. The generality of this space allows for polyhedral geometric processing methods to be conducted with ease. We demonstrate its usefulness in planar‐quadrilateral mesh subdivision, a resulting multiresolution editing algorithm, and novel shape‐space exploration with prescribed transformations.
Spectral Analysis on Medial Axis of 2D Shapes
(The Eurographics Association and John Wiley and Sons Ltd., 2014) He, Shuiqing; Choi, Yi‐King; Guo, Yanwen; Wang, Wenping; Oliver Deussen and Hao (Richard) Zhang
Shape analysis finds many important applications in shape understanding, matching and retrieval. Among the various shape analysis methods, spectral shape analysis aims to study the spectrum of the Laplace–Beltrami operator of some well‐designed shape‐dependent equations and obtain a spectral shape descriptor that can in turn be used for shape analysis purposes. The success of such approaches depends greatly on the discriminating power of a shape descriptor. On the other hand, the medial axis of a shape is widely known for its complete shape representation. It is sensitive to small perturbation of the boundary of a shape which often poses difficulty in its effective use for shape analysis. In this paper, we propose a new spectral shape descriptor, called the medial axis spectrum for 2D shapes, which directly applies spectral analysis to the medial axes of the shapes. We extend the Laplace–Beltrami operator onto the medial axis, and take the solution to an extended Laplacian eigenvalue problem defined on the axis as the medial axis spectrum. The medial axis spectrum is robust in the presence of shape boundary noise, and is invariant under rigid transformations, uniform scaling and isometry of the medial axis. We demonstrate these benefits of such a medial axis spectrum representation through extensive experiments. The medial axis spectrum is further used for 2D shape retrieval, and its superiority over previous work is shown by comparison.Shape analysis finds many important applications in shape understanding, matching and retrieval. Among the various shape analysis methods, spectral shape analysis aims to study the spectrum of the Laplace‐Beltrami operator of some well‐designed shape dependent equations and obtain a spectral shape descriptor that can in turn be used for shape analysis purposes. The success of such approaches depends greatly on the discriminating power of a shape descriptor. On the other hand, the medial axis of a shape is widely known for its complete shape representation. It is sensitive to small perturbation of the boundary of a shape which often poses difficulty in its effective use for shape analysis.
Higher Order Ray Marching
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Muñoz, Adolfo; Oliver Deussen and Hao (Richard) Zhang
Rendering participating media is still a challenging and time consuming task. In such media light interacts at every differential point of its path. Several rendering algorithms are based on ray marching: dividing the path of light into segments and calculating interactions at each of them. In this work, we revisit and analyze ray marching both as a quadrature integrator and as an initial value problem solver, and apply higher order adaptive solvers that ensure several interesting properties, such as faster convergence, adaptiveness to the mathematical definition of light transport and robustness to singularities. We compare several numerical methods, including standard ray marching and Monte Carlo integration, and illustrate the benefits of different solvers for a variety of scenes. Any participating media rendering algorithm that is based on ray marching may benefit from the application of our approach by reducing the number of needed samples (and therefore, rendering time) and increasing accuracy.Rendering participating media is still a challenging and time consuming task. In such media light interacts at every differential point of its path. Several rendering algorithms are based on ray marching: dividing the path of light into segments and calculating interactions at each of them. In this work, we revisit and analyze ray marching both as a quadrature integrator and as an initial value problem solver, and apply higher order adaptive solvers that ensure several interesting properties, such as faster convergence, adaptiveness to the mathematical definition of light transport and robustness to singularities. We compare several numerical methods, including standard ray marching and Monte Carlo integration, and illustrate the benefits of different solvers for a variety of scenes.
Editorial
(The Eurographics Association and Blackwell Publishing Ltd., 2014) Holly Rushmeier and Oliver Deussen
Interactive Diffraction from Biological Nanostructures
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Dhillon, D. S.; Teyssier, J.; Single, M.; Gaponenko, I.; Milinkovitch, M. C.; Zwicker, M.; Oliver Deussen and Hao (Richard) Zhang
We describe a technique for interactive rendering of diffraction effects produced by biological nanostructures, such as snake skin surface gratings. Our approach uses imagery from atomic force microscopy that accurately captures the geometry of the nanostructures responsible for structural colouration, that is, colouration due to wave interference, in a variety of animals. We develop a rendering technique that constructs bidirectional reflection distribution functions (BRDFs) directly from the measured data and leverages pre‐computation to achieve interactive performance. We demonstrate results of our approach using various shapes of the surface grating nanostructures. Finally, we evaluate the accuracy of our pre‐computation‐based technique and compare to a reference BRDF construction techniqueWe describe a technique for interactive rendering of diffraction effects produced by biological nanostructures, such as snake skin surface gratings. Our approach directly uses imagery from atomic force microscopy that accurately captures the geometry of the nanostructures responsible for structural colouration, that is, colouration due to wave interference, in a variety of animals.
Quad Layout Embedding via Aligned Parameterization
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Campen, M.; Kobbelt, L.; Oliver Deussen and Hao (Richard) Zhang
Quad layouting, i.e. the partitioning of a surface into a coarse network of quadrilateral patches, is a fundamental step in application scenarios ranging from animation and simulation to reverse engineering and meshing. This process involves determining the layout's combinatorial structure as well as its geometric embedding in the surface. We present a novel quad layout algorithm that focuses on the embedding optimization, thereby complementing recent methods focusing on the structure optimization aspect. It takes as input a description of the target layout structure and computes a complete embedding in form of a parameterization globally optimized for isometry and, in particular, principal direction alignment. Besides being suited for fully automatic workflows, our method can also incorporate user constraints and support the tedious but common procedure of manual layouting.Quad layouting, i.e. the partitioning of a surface into a coarse network of quadrilateral patches, is a fundamental step in application scenarios ranging from animation and simulation to reverse engineering and meshing. This process involves determining the layout's combinatorial structure as well as its geometric embedding in the surface. We present a novel quad layout algorithm that focuses on the embedding optimization, thereby complementing recent methods focusing on the structure optimization aspect. It takes as input a description of the target layout structure and computes a complete embedding in form of a parameterization globally optimized for isometry and, in particular, principal direction alignment.
Group‐in‐a‐Box Meta‐Layouts for Topological Clusters and Attribute‐Based Groups: Space‐Efficient Visualizations of Network Communities and Their Ties
(The Eurographics Association and John Wiley and Sons Ltd., 2014) Chaturvedi, S.; Dunne, C.; Ashktorab, Z.; Zachariah, R.; Shneiderman, B.; Oliver Deussen and Hao (Richard) Zhang
An important part of network analysis is understanding community structures like topological clusters and attribute‐based groups. Standard approaches for showing communities using colour, shape, rectangular bounding boxes, convex hulls or force‐directed layout algorithms remain valuable, however our Group‐in‐a‐Box meta‐layouts add a fresh strategy for presenting community membership, internal structure and inter‐cluster relationships. This paper extends the basic Group‐in‐a‐Box meta‐layout, which uses a Treemap substrate of rectangular regions whose size is proportional to community size. When there are numerous inter‐community relationships, the proposed extensions help users view them more clearly: (1) the Croissant–Doughnut meta‐layout applies empirically determined rules for box arrangement to improve space utilization while still showing inter‐community relationships, and (2) the Force‐Directed layout arranges community boxes based on their aggregate ties at the cost of additional space. Our free and open source reference implementation in NodeXL includes heuristics to choose what we have found to be the preferable Group‐in‐a‐Box meta‐layout to show networks with varying numbers or sizes of communities. Case study examples, a pilot comparative user preference study (nine participants), and a readability measure‐based evaluation of 309 Twitter networks demonstrate the utility of the proposed meta‐layouts.An important part of network analysis is understanding community structures like topological clusters and attribute‐based groups. Standard approaches for showing communities using color, shape, rectangular bounding boxes, convex hulls, or force‐directed layout algorithms remain valuable, however our Group‐in‐a‐Box meta‐layouts add a fresh strategy for presenting community membership, internal structure, and inter‐cluster relation‐ships. This paper extends the basic Group‐in‐a‐Box meta‐layout, which uses a Treemap substrate of rectangular regions whose size is

Browse

Browsing 33-Issue 8 by Issue Date

Results Per Page

Sort Options