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International Conference on computer graphics and Interactive Techniques, SIGGRAPH 2002

作者： Carr, Hamish Theußl, Thomas Moller, Torsten Department of Computer Science University of British Columbia VancouverBC Canada Institute of Computer Graphics and Algorithms Vienna University of Technology VancouverBC Austria Department of Computing Science Simon Fraser University VancouverBC Canada

ISBN: (纸本)1581135254

Theußl et al. [Theußl et al. 2001] showed that volumetric data sampled on a body-centred cubic (BCC) lattice is nearly 30% more efficient than data sampled on a cubic lattice, and produced volume renderings using splatting. We extend this work to generate isosurfaces based on the BCC lattice, and also on the hexagonal-close packed (HCP) grid. This sketch presents a modified version of marching octahedra that simplifies the BCC mesh to an octahedral mesh to reduce the number of triangles generated for the isosurface.

关键词： Volume rendering

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Untangling Circular Drawings: algorithms and Complexity 32

Untangling Circular Drawings: Algorithms and Complexity

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32nd International Symposium on algorithms and Computation, ISAAC 2021

作者： Bhore, Sujoy Li, Guangping Nöllenburg, Martin Rutter, Ignaz Wu, Hsiang-Yun Indian Institute of Science Education and Research Bhopal India Algorithms and Complexity Group TU Wien Austria Universität Passau Germany Research Unit of Computer Graphics TU Wien Austria

ISBN: (纸本)9783959772143

We consider the problem of untangling a given (non-planar) straight-line circular drawing δG of an outerplanar graph G = (V, E) into a planar straight-line circular drawing by shifting a minimum number of vertices to a new position on the circle. For an outerplanar graph G, it is clear that such a crossing-free circular drawing always exists and we define the circular shifting number shift◦(δG) as the minimum number of vertices that need to be shifted to resolve all crossings of δG. We show that the problem Circular Untangling, asking whether shift◦(δG) ≤ K for a given integer K, is NP-complete. Based on this result we study Circular Untangling for almost-planar circular drawings, in which a single edge is involved in all the crossings. In this case we provide a tight upper bound shift◦(δG) ≤ ⌊n2 ⌋ - 1, where n is the number of vertices in G, and present a polynomial-time algorithm to compute the circular shifting number of almost-planar drawings. © Sujoy Bhore, Guangping Li, Martin Nöllenburg, Ignaz Rutter, and Hsiang-Yun Wu.

关键词： Computational complexity

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Visual analytics for the exploration and assessment of segmentation errors

Visual analytics for the exploration and assessment of segme...

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2016 Eurographics Workshop on Visual Computing for Biology and Medicine, VCBM 2016

作者： Raidou, R.G. Marcelis, F.J.J. Breeuwer, M. Gröller, M.E. Vilanova, A. van de Wetering, H.M.M. Eindhoven University of Technology Netherlands Philips Healthcare Best Netherlands Institute of Computer Graphics and Algorithms Vienna University of Technology Austria VRVis Research Center Austria Delft University of Technology Netherlands

ISBN: (纸本)9783038680109

Several diagnostic and treatment procedures require the segmentation of anatomical structures from medical images. However, the automatic model-based methods that are often employed, may produce inaccurate segmentations. These, if used as input for diagnosis or treatment, can have detrimental effects for the patients. Currently, an analysis to predict which anatomic regions are more prone to inaccuracies, and to determine how to improve segmentation algorithms, cannot be performed. We propose a visual tool to enable experts, working on model-based segmentation algorithms, to explore and analyze the outcomes and errors of their methods. Our approach supports the exploration of errors in a cohort of pelvic organ segmentations, where the performance of an algorithm can be assessed. Also, it enables the detailed exploration and assessment of segmentation errors, in individual subjects. To the best of our knowledge, there is no other tool with comparable functionality. A usage scenario is employed to explore and illustrate the capabilities of our visual tool. To further assess the value of the proposed tool, we performed an evaluation with five segmentation experts. The evaluation participants confirmed the potential of the tool in providing new insight into their data and employed algorithms. They also gave feedback for future improvements. © 2016 The Author(s) Eurographics Proceedings © 2016 The Eurographics Association.

关键词： Errors

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Visual image query 02

Visual image query

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2nd International Symposium on Smart graphics, SMARTGRAPH '02

作者： Matković, Krešimir Neumann, László Siglaer, Johannes Kompast, Martin Purgathofer, Werner VRVis Research Center Vienna Austria Maros u. 36 H-1122 Budapest Hungary Institute for Design and Assessment of Technology TU Vienna Austria Institute of Computer Graphics and Algorithms TU Vienna Austria

ISBN: (纸本)1581135556

The explosion of storage media size and bandwidth has led to huge image databases. Methods are needed to find a particular image based on a crude description by the user. Keywording is not only tedious, but also subjective and therefore often incorrect. Available visual query systems have different properties, and are mostly based on some image transformation. An alternative visual query system is introduced, which finds an image similar to a user drawn sketch, or to any other reference image. A descriptor is created for each image in the database, and for the query image. Descriptors are compared in order to find the best matches. Descriptors are computed by inserting a limited number of quasi-random rectangles in the image, and computing the average colors of the rectangles. Furthermore, a reduced color histogram is computed and stored in the descriptor. The difference between descriptors is calculated as the weighted average of CIE LUV differences between corresponding rectangles. Using the Contrast Sensitivity Function this average is adapted to the users perception. The metric used for comparing images operates in the original image space, which makes the whole algorithm intuitive and easy to understand, and enables the comparison of images sections, as well. Copyright 2002 ACM.

关键词： Color

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Biopsy planner - Visual analysis for needle pathway planning in deep seated brain tumor biopsy

Biopsy planner - Visual analysis for needle pathway planning...

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14th Eurographics Conference on Visualization 2012, EuroVis 2012

作者： Herghelegiu, P.C. Manta, V. Perin, R. Bruckner, S. Gröller, E. Gheorghe Asachi Technical University of Iasi Romania Clinical Emergency Hospital Bagdasar-Arseni Bucharest Romania Institute of Computer Graphics and Algorithms Vienna University of Technology Austria

Biopsies involve taking samples from living tissue using a biopsy needle. In current clinical practice they are a first mandatory step before any further medical actions are planned. Performing a biopsy on a deep seated brain tumor requires considerable time for establishing and validating the desired biopsy needle pathway to avoid damage. In this paper, we present a system for the visualization, analysis, and validation of biopsy needle pathways. Our system uses a multi-level approach for identifying stable needle placements which minimize the risk of hitting blood vessels. This is one of the major dangers in this type of intervention. Our approach helps in identifying and visualizing the point on the pathway that is closest to a surrounding blood vessel, requiring a closer inspection by the neurosurgeon. An evaluation by medical experts is performed to demonstrate the utility of our system. © 2012 The Author(s).

关键词： Biopsy

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Isosurfaces on optimal regular samples

Isosurfaces on optimal regular samples

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5th Joint Eurographics - IEEE TCVG Symposium on Visualization, VisSym 2003

作者： Carr, Hamish Theußl, Thomas Möller, Torsten Department of Computer Science University of British Columbia VancouverBC Canada Institute of Computer Graphics and Algorithms Vienna University of Technology Vienna Austria Lab Simon Fraser University VancouverBC Canada

ISBN: (纸本)3905673010

Volumetric samples on Cartesian lattices are less ef_cient than samples on body-centred cubic (BCC) lattices. We show how to construct isosurfaces on BCC lattices using several different algorithms. Since the mesh that arises from BCC lattices involves a large number of cells, we show two alternate methods of reducing the number of cells by clumping tetrahedra into either octahedra or hexahedra. We also propose a theoretical model for estimating triangle counts for various algorithms, and present experimental results to show that isosurfaces generated using one of our algorithms can be competitive with isosurfaces generated using Marching Cubes on similar Cartesian grids. © 2003 Eurographics Association. All rights reserved.

关键词： Visualization

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Solving the post enrolment course timetabling problem by ant colony optimization 7

Solving the post enrolment course timetabling problem by ant...

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7th International Conference on the Practice and Theory of Automated Timetabling, PATAT 2008

作者： Mayer, Alfred Nothegger, Clemens Chwatal, Andreas Raidl, Günther R. Institute of Computer Graphics and Algorithms Vienna University of Technology Vienna Austria Christian Doppler Laboratory for Spatial Data from Laser Scanning and Remote Sensing Institute of Photogrammetry and Remote Sensing Vienna University of Technology Vienna Austria

In this work we present a new approach to tackle the problem of Post Enrolment Course Timetabling as specified for the International Timetabling Competition 2007 (ITC2007), competition track 2. The heuristic procedure is based on Ant Colony Optimization (ACO) where artificial ants successively construct solutions based on pheromones (stig-mergy) and local information. The key feature of our algorithm is the use of two distinct but simplified pheromone matrices (representing event–timeslot and event–room relations, respectively) in order to improve convergence but still provide enough flexibility for effectively guiding the solution construction process. Furthermore a local improvement method is embedded. We applied our algorithm to instances used for the First and Second International Timetabling Competition (TTComp2002 and ITC2007). The results document that our approach is among the leading algorithms for this problem;in many cases the optimal solution could be found. © Practice and Theory of Automated Timetabling, PATAT *** right reserved.

关键词： Ant colony optimization

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Improving the visualization of electron-microscopy data through optical flow interpolation

Improving the visualization of electron-microscopy data thro...

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27th Spring Conference on computer graphics, SCCG 2011

作者： Carata, Lucian Shao, Dan Hadwiger, Markus Groeller, Eduard Faculty of Automatic Control and Computer Engineering Gh. Asachi Technical University of Iasi Romania Institute of Computer Graphics and Algorithms Vienna University of Technology Austria Division of Mathematical and Computer Sciences and Engineering King Abdullah University of Science and Technology Saudi Arabia

ISBN: (纸本)9781450319782

Technical developments in neurobiology have reached a point where the acquisition of high resolution images representing individual neurons and synapses becomes possible. For this, the brain tissue samples are sliced using a diamond knife and imaged with electron-microscopy (EM). However, the technique achieves a low resolution in the cutting direction, due to limitations of the mechanical process, making a direct visualization of a dataset difficult. We aim to increase the depth resolution of the volume by adding new image slices interpolated from the existing ones, without requiring modifications to the EM image-capturing method. As classical interpolation methods do not provide satisfactory results on this type of data, the current paper proposes a re-framing of the problem in terms of motion volumes, considering the depth axis as a temporal axis. An optical flow method is adapted to estimate the motion vectors of pixels in the EM images, and this information is used to compute and insert multiple new images at certain depths in the volume. We evaluate the visualization results in comparison with interpolation methods currently used on EM data, transforming the highly anisotropic original dataset into a dataset with a larger depth resolution. The interpolation based on optical flow better reveals neurite structures with realistic undistorted shapes, and helps to easier map neuronal connections. © 2011 ACM.

关键词： Interpolation

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Contextual Snapshots: Enriched Visualization with Interactive Spatial Annotations 13

Contextual Snapshots: Enriched Visualization with Interactiv...

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Proceedings of the 29th Spring Conference on computer graphics

作者： Peter Mindek Stefan Bruckner M. Eduard Gröller Institute of Computer Graphics and Algorithms Vienna University of Technology Department of Informatics University of Bergen

ISBN: (纸本)9781450324809

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 are often dependent on other 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 be also 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 and the analysis of historical documents.

关键词： spatial selections annotations linked views provenance

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High-quality tactile paintings

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Journal on Computing and Cultural Heritage 2011年第2期4卷 5-5页

作者： Reichinger, Andreas Maierhofer, Stefan Purgathofer, Werner VRVis Forschungs-GmbH Vienna Austria Institute of Computer Graphics and Algorithms Vienna University of Technology Vienna Austria

The aim of this work is to bring the cultural heritage of two-dimensional art closer to being accessible by blind and visually impaired people. We present a computer-assisted workflow for the creation of tactile representations of paintings, suitable to be used as a learning tool in the context of guided tours in museums or galleries. Starting from high-resolution images of original paintings, our process allows an artist to quickly design the desired form, and generate data suitable for rapid prototyping machines to produce the physical touch tools. Laser-cut layered depth diagrams convey not only the individual objects in the painting and their spatial layout, but also augment their depth relations. CNC-milled textured reliefs additionally render fine details like brush strokes and texture suitable for the sense of touch. Our methods mimic aspects of the visual sense, make sure that the haptic output is quite faithful to the original paintings, and do not require special manual abilities like sculpting skills. © 2011 ACM.

关键词： Painting

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