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Now showing 1 - 10 of 20
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    IntenSelect: Using Dynamic Object Rating for Assisting 3D Object Selection
    (The Eurographics Association, 2005) Haan, Gerwin de; Koutek, Michal; Post, Frits H.; Erik Kjems and Roland Blach
    We present IntenSelect, a novel selection technique that dynamically assists the user in the selection of 3D objects in Virtual Environments. Ray-casting selection is commonly used, although it has limited accuracy and can be problematic in more difficult situations where the intended selection object is occluded or moving. Selection-byvolume techniques, which extend normal ray-casting, provide error tolerance to cope with the limited accuracy. However, these extensions generally are not usable in the more complex selection situations.We have devised a new selection-by-volume technique to create a more flexible selection technique which can be used in these situations. To achieve this, we use a new scoring function to calculate the score of objects, which fall within a user controlled, conic selection volume. By accumulating these scores for the objects, we obtain a dynamic, time-dependent, object ranking. The highest ranking object, or active object, is indicated by bending the otherwise straight selection ray towards it. As the selection ray is effectively snapped to the object, the user can now select the object more easily. Our user tests indicate that IntenSelect can improve the selection performance over ray-casting, especially in the more difficult cases of small objects. Furthermore, the introduced time-dependent object ranking proves especially useful when objects are moving, occluded and/or cluttered. Our simple scoring scheme can be easily extended for special purpose interaction such as widget or application specific interaction functionality, which creates new possibilities for complex interaction behavior.
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    Fast Normal Vector Compression with Bounded Error
    (The Eurographics Association, 2007) Griffith, E. J.; Koutek, M.; Post, Frits H.; Alexander Belyaev and Michael Garland
    We present two methods for lossy compression of normal vectors through quantization using base polyhedra. The first revisits subdivision-based quantization. The second uses fixed-precision barycentric coordinates. For both, we provide fast (de)compression algorithms and a rigorous upper bound on compression error. We discuss the effects of base polyhedra on the error bound and suggest polyhedra derived from spherical coverings. Finally, we present compression and decompression results, and we compare our methods to others from the literature.
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    Dynamic Visualisation of Orbital Fat Deformation using Anatomy-Guided Interaction
    (The Eurographics Association, 2010) Schaafsma, Peter J.; Schutte, Sander; Simonsz, Huib J.; Post, Frits H.; Botha, Charl P.; Dirk Bartz and Charl Botha and Joachim Hornegger and Raghu Machiraju and Alexander Wiebel and Bernhard Preim
    The human eye is a biomechanical system. Orbital fat plays an important role in the working of this system, but its behaviour during eye movement is not well understood. To give insight into this behaviour, visualisation is a useful tool. This paper presents a complete pipeline for interactive particle-based visualisation and exploration of orbital fat deformation from MRI data. Sensible 3D particle seeding is important in this type of visualisation. We address that problem with a two-step process: Interactive, anatomy-guided slice positioning, and contour-based region of interest specification. Since the deformation calculation is unlikely to be correct everywhere, we derive and visualise an uncertainty measure based on deformed and original MRI data. We also performed a case study evaluation to investigate the benefits of our approach towards orbital fat deformation visualisation.
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    Over Two Decades of Integration-Based, Geometric Flow Visualization
    (The Eurographics Association, 2009) McLoughlin, Tony; Laramee, Robert S.; Peikert, Ronald; Post, Frits H.; Chen, Min; M. Pauly and G. Greiner
    Flow visualization is a fascinating sub-branch of scientific visualization. With ever increasing computing power, it is possible to process ever more complex fluid simulations. However, a gap between data set sizes and our ability to visualize them remains. This is especially true for the field of flow visualization which deals with large, timedependent, multivariate simulation datasets. In this paper, geometry based flow visualization techniques form the focus of discussion. Geometric flow visualization methods place discrete objects in the vector field whose characteristics reflect the underlying properties of the flow. A great amount of progress has been made in this field over the last two decades. However, a number of challenges remain, including placement, speed of computation, and perception. In this survey, we review and classify geometric flow visualization literature according to the most important challenges when considering such a visualization, a central theme being the seeding object upon which they are based. This paper details our investigation into these techniques with discussions on their applicability and their relative merits and drawbacks. The result is an up-to-date overview of the current state-of-the-art that highlights both solved and unsolved problems in this rapidly evolving branch of research. It also serves as a concise introduction to the field of flow visualization research.
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    Virtual Spring Manipulators for Particle Steering in Molecular Dynamics on the ResponsiveWorkbench
    (The Eurographics Association, 2002) Koutek, Michal; Hees, Jeroen van; Post, Frits H.; Bakker, A.F.; S. Mueller and W. Stuerzlinger
    In this paper we present new virtual spring manipulator-based tools for steering particles in molecular dynamics simulations in virtual environments. We briefly overview the MolDRIVE system, our visualization and computational steering environment for molecular dynamics real-time simulations, which is the platform for our particle steering implementation. Our study concentrates on visual feedback tools. We compare a basic virtual particle steering method with two other methods using a spring manipulator. The first just creates a visual feedback of a flexible connection between the user s interaction device and the steered particle, while the second technique creates a visual illusion of force feedback. The user can, through the spring manipulator, exert a force on the manipulated particle in the MD simulation. All presented particle steering tools are intuitive and easy to use.
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    Interactive Previewing for Transfer Function Specification in Volume Rendering
    (The Eurographics Association, 2002) Botha, Charl P.; Post, Frits H.; D. Ebert and P. Brunet and I. Navazo
    This paper presents a new technique for supplying meaningful visual feedback during direct volume rendering transfer function specification. The technique uses meta-data calculated during a pre-processing step to generate interactively an approximate volume rendering that is voxel-registered with a single user-selected slice. Because of the registration, this preview can easily be alpha-blended with a grey-scale image of the data that is being volume rendered. In this way, the user gets real-time visual feedback on her transfer function specification with regards to both the expected composited optical properties and the "fidelity" (how closely the rendering matches the original data) of the resulting rendering.
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    Direct Visualization of Deformation in Volumes
    (The Eurographics Association and Blackwell Publishing Ltd., 2009) Busking, Stef; Botha, Charl P.; Post, Frits H.; H.-C. Hege, I. Hotz, and T. Munzner
    Deformation is a topic of interest in many disciplines. In particular in medical research, deformations of surfaces and even entire volumetric structures are of interest. Clear visualization of such deformations can lead to important insight into growth processes and progression of disease. We present new techniques for direct focus+context visualization of deformation fields representing transformations between pairs of volumetric datasets. Typically, such fields are computed by performing a non-rigid registration between two data volumes. Our visualization is based on direct volume rendering and uses the GPU to compute and interactively visualize features of these deformation fields in real-time. We integrate visualization of the deformation field with visualization of the scalar volume affected by the deformations. Furthermore, we present a novel use of texturing in volume rendered visualizations to show additional properties of the vector field on surfaces in the volume.
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    Surface Curvature Line Clustering for Polyp Detection in CT Colonography
    (The Eurographics Association, 2008) Zhao, Lingxiao; Ravesteijn, Vincent F. van; Botha, Charl P.; Truyen, Roel; Vos, Frans M.; Post, Frits H.; Charl Botha and Gordon Kindlmann and Wiro Niessen and Bernhard Preim
    Automatic polyp detection is a helpful addition to laborious visual inspection in CT colonography. Traditional detection methods are based on calculating image features at discrete positions on the colon wall. However large-scale surface shapes are not captured. This paper presents a novel approach to aggregate surface shape information for automatic polyp detection. The iso-surface of the colon wall can be partitioned into geometrically homogeneous regions based on clustering of curvature lines, using a spectral clustering algorithm and a symmetric line similarity measure. Each partition corresponds with the surface area that is covered by a single cluster. For each of the clusters, a number of features are calculated, based on the volumetric shape index and the surface curvedness, to select the surface partition corresponding to the cap of a polyp. We have applied our clustering approach to nine annotated patient datasets. Results show that the surface partition-based features are highly correlated with true polyp detections and can thus be used to reduce the number of false-positive detections.
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    The State of the Art in Flow Visualisation: Feature Extraction and Tracking
    (Blackwell Publishing, Inc and Eurographics Association, 2003) Post, Frits H.; Vrolijk, Benjamin; Hauser, Helwig; Laramee, Robert S.; Doleisch, Helmut
    Flow visualisation is an attractive topic in data visualisation, offering great challenges for research. Very large data sets must be processed, consisting of multivariate data at large numbers of grid points, often arranged in many time steps. Recently, the steadily increasing performance of computers again has become a driving force for new advances in flow visualisation, especially in techniques based on texturing, feature extraction, vector field clustering, and topology extraction.In this article we present the state of the art in feature-based flow visualisation techniques. We will present numerous feature extraction techniques, categorised according to the type of feature. Next, feature tracking and event detection algorithms are discussed, for studying the evolution of features in time-dependent data sets. Finally, various visualisation techniques are demonstrated.ACM CSS: I.3.8 Computer Graphics-applications
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    Hybrid Interfaces in VEs: Intent and Interaction
    (The Eurographics Association, 2006) Haan, Gerwin de; Griffith, Eric J.; Koutek, Michal; Post, Frits H.; Ming Lin and Roger Hubbold
    Hybrid user interfaces (UIs) integrate well-known 2D user interface elements into the 3D virtual environment, and provide a familiar and portable interface across a variety of VR systems. However, their usability is often reduced by accuracy and speed, caused by inaccuracies in tracking and a lack of constraints and feedback. To ease these difficulties often large widgets and bulky interface elements must be used, which, at the same time, limit the size of the 3D workspace and restrict the space where other supplemental 2D information can be displayed. In this paper, we present two developments addressing this problem: supportive user interaction and a new implementation of a hybrid interface. First, we describe a small set of tightly integrated 2D windows we developed with the goal of providing increased flexibility in the UI and reducing UI clutter. Next we present extensions to our supportive selection technique, IntenSelect. To better cope with a variety of VR and UI tasks, we extended the selection assistance technique to include direct selection, spring-based manipulation, and specialized snapping behavior. Finally, we relate how the effective integration of these two developments eases some of the UI restrictions and produces a more comfortable VR experience.