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  • 1. Bachynskyi, M.
    et al.
    Oulasvirta, A.
    Palmas, Gregorio
    Max Planck Institute for Informatics, Germany.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Biomechanical Simulation in the Analysis of Aimed Movements2013In: Extended Abstracts (Works in Progress) CHI’13, ACM Digital Library, 2013, 1-6 p.Conference paper (Refereed)
    Abstract [en]

    For efficient design of gestural user interfaces both performance and fatigue characteristics of movements must be understood. We are developing a novel method that allows for biomechanical analysis in conjunction with performance analysis. We capture motion data using optical tracking from which we can compute performance measures such as speed and accuracy. The measured motion data also serves as input for a biomechanical simulation using inverse dynamics and static optimization on a full-body skeletal model. The simulation augments the data by biomechanical quantities from which we derive an index of fatigue. We are working on an interactive analysis tool that allows practitioners to identify and compare movements with desirable performance and fatigue properties. We show the applicability of our methodology using a case study of rapid aimed movements to targets covering the 3D movement space uniformly.

  • 2. Bachynskyi, M.
    et al.
    Oulasvirta, A.
    Palmas, Gregorio
    Max Planck Institute for Informatics, Germany.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Is Motion Capture-Based Biomechanical Simulation Valid for HCI Studies?: Study and Implications2014In: Proc. ACM CHI Conference on Human Factors in Computing Systems, ACM Digital Library, 2014, 3215-3224 p.Conference paper (Refereed)
    Abstract [en]

    Motion-capture-based biomechanical simulation is a non-invasive analysis method that yields a rich description of posture, joint, and muscle activity in human movement. The method is presently gaining ground in sports, medicine, and industrial ergonomics, but it also bears great potential for studies in HCI where the physical ergonomics of a design is important. To make the method more broadly accessible, we study its predictive validity for movements and users typical to studies in HCI. We discuss the sources of error in biomechanical simulation and present results from two validation studies conducted with a state-of-the-art system. Study I tested aimed movements ranging from multitouch gestures to dancing, finding out that the critical limiting factor is the size of movement. Study II compared muscle activation predictions to surface-EMG recordings in a 3D pointing task. The data shows medium-to-high validity that is, however, constrained by some characteristics of the movement and the user. We draw concrete recommendations to practitioners and discuss challenges to developing the method further.

  • 3. Bachynskyi, M.
    et al.
    Palmas, Gregorio
    Max Planck Institute for Informatics, Germany.
    Oulasvirta, A.
    Steimle, J.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Performance and Ergonomics of Touch Surfaces: A Comparative Study Using Biomechanical Simulation2015In: CHI '15: Proceedings of the 33rd Annual ACM Conference on Human Factors in Computing, ACM Digital Library, 2015, 1817-1826 p.Conference paper (Refereed)
    Abstract [en]

    Although different types of touch surfaces have gained extensive attention in HCI, this is the first work to directly compare them for two critical factors: performance and ergonomics. Our data come from a pointing task (N=40) carried out on five common touch surface types: public display (large, vertical, standing), tabletop (large, horizontal, seated), laptop (medium, adjustably tilted, seated), tablet (seated, in hand), and smartphone (single- and two-handed input). Ergonomics indices were calculated from biomechanical simulations of motion capture data combined with recordings of external forces. We provide an extensive dataset for researchers and report the first analyses of similarities and differences that are attributable to the different postures and movement ranges.

  • 4. Bachynskyi, M.
    et al.
    Palmas, Gregorio
    Max Planck Institute for Informatics, Germany.
    Oulasvirta, A.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Informing the Design of Novel Input Methods with Muscle Coactivation Clustering2015In: ACM Transactions on Computer-Human Interaction, ISSN 1073-0516, Vol. 21, no 6, 30Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel summarization of biomechanical and performance data for user interface designers. Previously, there was no simple way for designers to predict how the location, direction, velocity, precision, or amplitude of users’ movement affects performance and fatigue. We cluster muscle coactivation data from a 3D pointing task covering the whole reachable space of the arm. We identify eleven clusters of pointing movements with distinct muscular, spatio-temporal and performance properties. We discuss their use as heuristics when designing for 3D pointing.

  • 5. Benger, W.
    et al.
    Heinzl, R.
    Hildenbrand, D.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Theisel, H.
    Tschumperlé, D.
    Differential Methods for Multi-Dimensional Visual Data Analysis2010In: Handbook of Mathematical Methods in Imaging / [ed] Scherzer, O., Springer , 2010, 1533-1595 p.Chapter in book (Other academic)
    Abstract [en]

    Images in scientific visualization are the end-product of the data processing. Starting from higher-dimensional datasets, such as scalar-, vector-, tensor- fields given on 2D, 3D, 4D domains, the objective is to reduce this complexity to two-dimensional images comprehensible to the human visual system. Various mathematical fields such as in particular differential geometry, topology (theory of discretized manifolds), differential topology, linear algebra, geometric algebra, vectorfield and tensor analysis, and partial differential equations contribute to the data filtering and transformation algorithms used in scientific visualization. The application of differential methods is core to all these fields. The following chapter will provide examples from current research on the application of these mathematical domains to scientific visualization and ultimately generating of images for analysis of multi-dimensional datasets.

  • 6. Brunton, A.
    et al.
    Wand, M.
    Wuhrer, S.
    Seidel, H. -P
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    A Low-Dimensional Representation for Robust Partial Isometric Correspondences Computation2014In: Graphical Models, ISSN 1524-0703, E-ISSN 1524-0711, Vol. 76, no 2, 70-85 p.Article in journal (Refereed)
    Abstract [en]

    Intrinsic shape matching has become the standard approach for pose invariant correspondence estimation among deformable shapes. Most existing approaches assume global consistency. While global isometric matching is well understood, only a few heuristic solutions are known for partial matching. Partial matching is particularly important for robustness to topological noise, which is a common problem in real-world scanner data. We introduce a new approach to partial isometric matching based on the observation that isometries are fully determined by local information: a map of a single point and its tangent space fixes an isometry. We develop a new representation for partial isometric maps based on equivalence classes of correspondences between pairs of points and their tangent-spaces. We apply our approach to register partial point clouds and compare it to the state-of-the-art methods, where we obtain significant improvements over global methods for real-world data and stronger guarantees than previous partial matching algorithms.

  • 7. Funck, W. von
    et al.
    Weinkauf, Tino
    Visualization and Data Analysis, Zuse Inst Berlin, Berlin, Germany.
    Theisel, H.
    Seidel, H. -P
    Smoke Surfaces: An Interactive Flow Visualization Technique Inspired by Real-World Flow Experiments2008In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 14, no 6, 1396-1403 p.Article in journal (Refereed)
    Abstract [en]

    Smoke rendering is a standard technique for flow visualization. Most approaches are based on a volumetric, particle based, or image based representation of the smoke. This paper introduces an alternative representation of smoke structures: as semi-transparent streak surfaces. In order to make streak surface integration fast enough for interactive applications, we avoid expensive adaptive retriangulations by coupling the opacity of the triangles to their shapes. This way, the surface shows a smoke-like look even in rather turbulent areas. Furthermore, we show modifications of the approach to mimic smoke nozzles, wool tufts, and time surfaces. The technique is applied to a number of test data sets.

  • 8. Günther, B.
    et al.
    Thiele, F.
    Petz, R.
    Nitsche, W.
    Sahner, J.
    Weinkauf, Tino
    Zuse Institute Berlin, Germany; Department Visualization and Data Analysis, Germany.
    Hege, H. -C
    Control of Separation on the Flap of a Three-Element High-Lift Configuration2007In: 45th AIAA Aerospace Sciences Meeting and Exhibit, AIAA , 2007, Vol. 5Conference paper (Refereed)
    Abstract [en]

    This paper describes a joint experimental and numerical investigation of the control of the flow over the flap of a three-element high-lift configuration by means of periodic excitation. At Reynolds numbers between 0.3 ᅵ 106 and 1 ᅵ 106 the flow is influenced by periodic blowing or periodic blowing/suction through slots near the flap leading edge. The delay of flow separation by periodic vertical excitation could be identified in the experiments as well as numerical simulations based on the Unsteady Reynolds-averaged Navier-Stokes equations (URANS). As a result, the mean aerodynamic lift of this practically relevant wing configuration could be significantly enhanced. By investigating different excitation frequencies and intensities optimum control parameters could be found. The behaviour of the aerodynamic forces with varying flap deflection angle are measured on a finite swept wing. Scientific visualisation of the numerical simulations of an infinite swept wing allows a detailed analysis of the structures in this complex flow field and the effect of flow control on these.

  • 9. Günther, D.
    et al.
    Jacobson, A.
    Reininghaus, J.
    Seidel, H. -P
    Sorkine-Hornung, O.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Fast and Memory-Efficient Topological Denoising of 2D and 3D Scalar Fields2014In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 20, no 12, 2585-2594 p.Article in journal (Refereed)
    Abstract [en]

    Data acquisition, numerical inaccuracies, and sampling often introduce noise in measurements and simulations. Removing this noise is often necessary for efficient analysis and visualization of this data, yet many denoising techniques change the minima and maxima of a scalar field. For example, the extrema can appear or disappear, spatially move, and change their value. This can lead to wrong interpretations of the data, e.g., when the maximum temperature over an area is falsely reported being a few degrees cooler because the denoising method is unaware of these features. Recently, a topological denoising technique based on a global energy optimization was proposed, which allows the topology-controlled denoising of 2D scalar fields. While this method preserves the minima and maxima, it is constrained by the size of the data. We extend this work to large 2D data and medium-sized 3D data by introducing a novel domain decomposition approach. It allows processing small patches of the domain independently while still avoiding the introduction of new critical points. Furthermore, we propose an iterative refinement of the solution, which decreases the optimization energy compared to the previous approach and therefore gives smoother results that are closer to the input. We illustrate our technique on synthetic and real-world 2D and 3D data sets that highlight potential applications.

  • 10. Günther, D.
    et al.
    McGuire, P. C.
    Walter, S.
    Weinkauf, Tino
    New York University, USA.
    Hege, H. -C
    Extraction of Valley Networks in Mars Elevation Maps2010In: European Planetary Science Congress (Poster), Europea Planetary Science Congress , 2010Conference paper (Refereed)
    Abstract [en]

    The identification of valley networks and channels is an essential tool for geomorphological interpretations of the fluvial, glacial and volcanic history of Mars. While the creation of valley networks by erosion is an accepted hypothesis, the flow of water as the sole cause has recently been put into question. To investigate the origin of the networks, their detailed properties have to be mapped at a global scale. In previous attempts of computer-generated global mapping, manual verification of the results was necessary. Herein, we present a novel algorithm to automatically extract valley networks in terms of extremal lines and compare the extraction results with an area that has already been manually mapped in the literature. Extremal lines are a subset of the topological skeleton from an elevation map. The skeleton encodes the essential information and can be iteratively simplified to obtain different levels of detail in the elevation map. The hierarchization process is thereby fully automatic and does not involve any algorithmic parameters. Using the measure separatrix persistence, we are able to assess the topological importance of each element of the skeleton. This enables a reduction to the most dominant extremal lines. This topological analysis allows for an unbiased extraction of all extremal lines in an elevation map. The data analyst is provided with a slider to choose an appropriate level of detail for further analysis.

  • 11. Günther, D.
    et al.
    Reininghaus, J.
    Prohaska, S.
    Weinkauf, Tino
    New York University, U.S.A..
    Hege, H. -C
    Efficient Computation of a Hierarchy of Discrete 3D Gradient Vector Fields2012In: Topological Methods in Data Analysis and Visualization II / [ed] Peikert, R.; Hauser, H.; Carr, H.; Fuchs, R., Springer, 2012, 15-30 p.Chapter in book (Other academic)
    Abstract [en]

    This paper introduces a novel combinatorial algorithm to compute a hierarchy of discrete gradient vector fields for three-dimensional scalar fields. The hierarchy is defined by an importance measure and represents the combinatorial gradient flow for different levels of detail. The presented algorithm is based on Forman’s discrete Morse theory, which guarantees topological consistency and algorithmic robustness. In contrast to previous work, our algorithm combines memory and runtime efficiency. It thereby lends itself to the analysis of large data sets. A discrete gradient vector field is also a compact representation of the underlying extremal structures - the critical points, separation lines and surfaces. Given a certain level of detail, an explicit geometric representation of these structures can be extracted using simple and fast graph algorithms.

  • 12. Günther, D.
    et al.
    Reininghaus, J.
    Seidel, H. -P
    Weinkauf, Tino
    CNRS LTCI Institut Mines-Télécom, France .
    Notes on the Simplification of the Morse-Smale Complex2014In: Topological Methods in Data Analysis and Visualization III / [ed] Bremer, P. -T; Hotz, I.; Pascucci, V.; Peikert, R., Springer, 2014, 135-150 p.Chapter in book (Other academic)
    Abstract [en]

    The Morse-Smale complex can be either explicitly or implicitly represented. Depending on the type of representation, the simplification of the Morse-Smale complex works differently. In the explicit representation, the Morse-Smale complex is directly simplified by explicitly reconnecting the critical points during the simplification. In the implicit representation, on the other hand, the Morse-Smale complex is given by a combinatorial gradient field. In this setting, the simplification changes the combinatorial flow, which yields an indirect simplification of the Morse-Smale complex. The topological complexity of the Morse-Smale complex is reduced in both representations. However, the simplifications generally yield different results. In this paper, we emphasize the differences between these two representations, and provide a high-level discussion about their advantages and limitations.

  • 13. Günther, D.
    et al.
    Seidel, H. -P
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany .
    Extraction of Dominant Extremal Structures in Volumetric Data using Separatrix Persistence2012In: Computer graphics forum (Print), ISSN 0167-7055, E-ISSN 1467-8659, Vol. 31, no 8, 2554-2566 p.Article in journal (Refereed)
    Abstract [en]

    Extremal lines and surfaces are features of a 3D scalar field where the scalar function becomes minimal or maximal with respect to a local neighborhood. These features are important in many applications, e.g., computer tomography, fluid dynamics, cell biology. We present a novel topological method to extract these features using discrete Morse theory. In particular, we extend the notion of Separatrix Persistence from 2D to 3D, which gives us a robust estimation of the feature strength for extremal lines and surfaces. Not only does it allow us to determine the most important (parts of) extremal lines and surfaces, it also serves as a robust filtering measure of noise-induced structures. Our purely combinatorial method does not require derivatives or any other numerical computations.

  • 14. Hege, H. -C
    et al.
    Weinkauf, Tino
    Zuse Institute Berlin, Germany.
    Prohaska, S.
    Hutanu, A.
    Distributed Visualization and Analysis of Fluid Dynamics Data2004In: Proc. Fourth International Symposium on Advanced Fluid Information and Transdisciplinary Fluid Integration, 2004Conference paper (Refereed)
    Abstract [en]

    Fluid dynamics applications require a good understanding of the underlying physical phenomena. Therefore, effective procedures are necessary for analyzing and visualizing the various physical fields. Beside interactive and perceptually efficient techniques for visualizing flow fields directly, there is strong demand for methods that uncover hidden flow structures. %as well as the structural changes due to parameter variations. Some recently developed feature based visual analysis methods are exemplarily presented. Fluid flow data typically are large and often are stored remotely or distributedly. The interactive visual analysis of such large data sets requires new software architectures – ideally utilizing emerging Grid standards. We discuss such architectures and report on specific realizations in the framework of the visualization system Amira.

  • 15. Hege, H. -C
    et al.
    Weinkauf, Tino
    Zuse Institute, Germany.
    Prohaska, S.
    Hutanu, A.
    Towards Distributed Visualization and Analysis of Large Flow Data2005In: JSME international journal. Series B, Fluids and thermal engineering, ISSN 1340-8054, E-ISSN 1347-5371, Vol. 48, no 2, 241-246 p.Article in journal (Refereed)
    Abstract [en]

    Fluid dynamics applications require a good understanding of the underlying physical phenomena. Therefore, effective procedures are necessary for analyzing and visualizing the various physical fields. Beside interactive and perceptually efficient techniques for visualizing flow fields directly, there is strong demand for methods that uncover hidden flow structures. Some recently developed feature based visual analysis methods are exemplarily presented. Fluid flow data typically are large and often are stored remotely or distributedly. The interactive visual analysis of such large data sets requires new software architectures – ideally utilizing emerging Grid standards. We discuss such architectures and report on specific software realizations.

  • 16. Jacobson, A.
    et al.
    Weinkauf, Tino
    MPI Informatik, Germany.
    Sorkine, O.
    Smooth Shape-Aware Functions with Controlled Extrema2012In: Computer graphics forum (Print), ISSN 0167-7055, E-ISSN 1467-8659, Vol. 31, no 5, 1577-1586 p.Article in journal (Refereed)
    Abstract [en]

    Functions that optimize Laplacian-based energies have become popular in geometry processing, e.g. for shape deformation, smoothing, multiscale kernel construction and interpolation. Minimizers of Dirichlet energies, or solutions of Laplace equations, are harmonic functions that enjoy the maximum principle, ensuring no spurious local extrema in the interior of the solved domain occur. However, these functions are only C0 at the constrained points, which often causes smoothness problems. For this reason, many applications optimize higher-order Laplacian energies such as biharmonic or triharmonic. Their minimizers exhibit increasing orders of continuity but also increasing oscillation, immediately releasing the maximum principle. In this work, we identify characteristic artifacts caused by spurious local extrema, and provide a framework for minimizing quadratic energies on manifolds while constraining the solution to obey the maximum principle in the solved region. Our framework allows the user to specify locations and values of desired local maxima and minima, while preventing any other local extrema. We demonstrate our method on the smoothness energies corresponding to popular polyharmonic functions and show its usefulness for fast handle-based shape deformation, controllable color diffusion, and topologically-constrained data smoothing.

  • 17. Kasten, J.
    et al.
    Weinkauf, Tino
    Courant Institute of Mathematical Sciences, USA.
    Petz, C.
    Hotz, I.
    Noack, B. R.
    Hege, H. -C
    Extraction of Coherent Structures from Natural and Actuated Flows2010In: Active Flow Control II / [ed] King, R., Springer, 2010, 373-387 p.Chapter in book (Other academic)
    Abstract [en]

    We present feature-extraction techniques for numerical and experimental data of complex fluid flows. Focus is placed on efficient analysis and visualization of coherent structures of snapshots, temporal evolution and parameter-dependency of coherent structures. One key enabler are Galilean invariant flow quantities based on pressure, acceleration, vorticity and velocity Jacobians. Other important catalyzers are Lagrangian filters that distill persistent strong particle-fixed features while neglecting weak and short-living ones. The proposed feature extraction framework is exemplified for the time-dependent natural and actuated flow around a high-lift airfoil, as well as other benchmark configurations of the SFB 557.

  • 18. Kozlov, Y.
    et al.
    Esturo, J. Martinez
    Seidel, H. -P
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Regularized Harmonic Surface Deformation2014Other (Other academic)
    Abstract [en]

    Harmonic surface deformation is a well-known geometric modeling method that creates plausible deformations in an interactive manner. However, this method is susceptible to artifacts, in particular close to the deformation handles. These artifacts often correlate with strong gradients of the deformation energy. In this work, we propose a novel formulation of harmonic surface deformation, which incorporates a regularization of the deformation energy. To do so, we build on and extend a recently introduced generic linear regularization approach. It can be expressed as a change of norm for the linear optimization problem, i.e., the regularization is baked into the optimization. This minimizes the implementation complexity and has only a small impact on runtime. Our results show that a moderate use of regularization suppresses many deformation artifacts common to the well-known harmonic surface deformation method, without introducing new artifacts.

  • 19. Kuhn, A.
    et al.
    Rössl, C.
    Weinkauf, Tino
    Max Planck Institute for Informatics.
    Theisel, H.
    A Benchmark for Evaluating FTLE Computations2012In: Proc. IEEE PacificVis, IEEE Computer Society, 2012, 121-128 p.Conference paper (Refereed)
    Abstract [en]

    The Finite Time Lyapunov Exponent (FTLE) has become a widespread tool for analyzing unsteady flow behavior. For its computation, several numerical methods have been introduced, which provide trade-offs between performance and accuracy. In order to decide which methods and parameter settings are suitable for a particular application, an evaluation of the different FTLE methods is necessary. We propose a general benchmark for FTLE computation, which consists of a number of 2D time-dependent flow fields and error measures. Evaluating the accuracy of a numerically computed FTLE field requires a ground truth, which is not available for realistic flow data sets, since such fields can generally not be described in a closed form. To overcome this, we introduce approaches to create non-trivial vector fields with a closed-form formulation of the FTLE field. Using this, we introduce a set of benchmark flow data sets that resemble relevant geometric aspects of Lagrangian structures, but have an analytic solution for FTLE. Based on this ground truth, we perform a comparative evaluation of three standard FTLE concepts. We suggest error measures based on the variance of both, the fields and the extracted ridge structures.

  • 20. Laramee, R. S.
    et al.
    Erlebacher, G.
    Garth, C.
    Schafhitzel, T.
    Theisel, H.
    Tricoche, X.
    Weinkauf, Tino
    Konrad Zuse Zentrum Informat Tech Berlin, Germany.
    Weiskopf, D.
    Applications of Texture-Based Flow Visualization2008In: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 2, no 3, 264-274 p.Article in journal (Refereed)
    Abstract [en]

    Flow visualization is a classic sub-field of scientific visualization. The task of flow visualization algorithms is to depict vector data, i.e., data with magnitude and direction. An important category of flow visualization techniques makes use primarily of textures in order to convey the properties of a vector field. Recently, several research advances have been made in this special category, of dense, texture-based techniques. We present the application of the most recent texture-based techniques to real world data from (1) oceanography and meteorology, (2) computational fluid dynamics (CFD) in the automotive industry, and (3) medicine. We describe the motivations for using texture-based algorithms as well as the important recent advancements required for their successful incorporation into industry grade software. Our goal is to appeal to practitioners in the field interested in learning how these recent techniques can help them gain insight into problems that engineers and other professionals may be faced with on a daily basis. Many of these applications have only recently become possible.

  • 21.
    Larsson, David
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Insitutet, Sweden.
    Spühler, Jeannette
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Günyeli, E.
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Hoffman, Johan
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Colarieti-Tosti, Massimiliano
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Winter, R.
    Larsson, Matilda
    KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging. Karolinska Institutet, Sweden.
    Estimation of left ventricular blood flow parameters: Clinical application of patient-specific CFD simulations from 4D echocardiography2017In: Medical Imaging 2017: Ultrasonic Imaging and Tomography, SPIE - International Society for Optical Engineering, 2017, Vol. 10139, 101390LConference paper (Refereed)
    Abstract [en]

    Echocardiography is the most commonly used image modality in cardiology, assessing several aspects of cardiac viability. The importance of cardiac hemodynamics and 4D blood flow motion has recently been highlighted, however such assessment is still difficult using routine echo-imaging. Instead, combining imaging with computational fluid dynamics (CFD)-simulations has proven valuable, but only a few models have been applied clinically. In the following, patient-specific CFD-simulations from transthoracic dobutamin stress echocardiography have been used to analyze the left ventricular 4D blood flow in three subjects: two with normal and one with reduced left ventricular function. At each stress level, 4D-images were acquired using a GE Vivid E9 (4VD, 1.7MHz/3.3MHz) and velocity fields simulated using a presented pathway involving endocardial segmentation, valve position identification, and solution of the incompressible Navier-Stokes equation. Flow components defined as direct flow, delayed ejection flow, retained inflow, and residual volume were calculated by particle tracing using 4th-order Runge-Kutta integration. Additionally, systolic and diastolic average velocity fields were generated. Results indicated no major changes in average velocity fields for any of the subjects. For the two subjects with normal left ventricular function, increased direct flow, decreased delayed ejection flow, constant retained inflow, and a considerable drop in residual volume was seen at increasing stress. Contrary, for the subject with reduced left ventricular function, the delayed ejection flow increased whilst the retained inflow decreased at increasing stress levels. This feasibility study represents one of the first clinical applications of an echo-based patient-specific CFD-model at elevated stress levels, and highlights the potential of using echo-based models to capture highly transient flow events, as well as the ability of using simulation tools to study clinically complex phenomena. With larger patient studies planned for the future, and with the possibility of adding more anatomical features into the model framework, the current work demonstrates the potential of patient-specific CFD-models as a tool for quantifying 4D blood flow in the heart.

  • 22. Max, N.
    et al.
    Weinkauf, Tino
    Zuse Institute Berlin, Germany.
    Critical Points of the Electric Field from a Collection of Point Charges2009In: Topology-Based Methods in Visualization II / [ed] Hege, H. -C; Polthier, K.; Scheuermann, G., Springer , 2009, 101-114 p.Chapter in book (Other academic)
    Abstract [en]

    The electric field around a molecule is generated by the charge distribution of its constituents: positively charged atomic nuclei, which are well approximated by point charges, and negatively charged electrons, whose probability density distribution can be computed from quantum mechanics. For the purposes of molecular mechanics or dynamics, the charge distribution is often approximated by a collection of point charges, with either a single partial charge at each atomic nucleus position, representing both the nucleus and the electrons near it, or as several different point charges per atom. The critical points in the electric field are useful in visualizing its geometrical and topological structure, and can help in understanding the forces and motion it induces on a charged ion or neutral dipole. Most visualization tools for vector fields use only samples of the field on the vertices of a regular grid, and some sort of interpolation, for example, trilinear, on the grid cells. There is less risk of missing or misinterpreting topological features if they can be derived directly from the analytic formula for the field, rather than from its samples. This work presents a method which is guaranteed to find all the critical points of the electric field from a finite set of point charges. To visualize the field topology, we have modified the saddle connector method to use the analytic formula for the field.

  • 23. Micallef, Luana
    et al.
    Palmas, Gregorio
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Oulasvirta, Antti
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Towards Perceptual Optimization of the Visual Design of Scatterplots2017In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 23, no 6, 1588-1599 p.Article in journal (Refereed)
    Abstract [en]

    Designing a good scatterplot can be difficult for non-experts in visualization, because they need to decide on many parameters, such as marker size and opacity, aspect ratio, color, and rendering order. This paper contributes to research exploring the use of perceptual models and quality metrics to set such parameters automatically for enhanced visual quality of a scatterplot. A key consideration in this paper is the construction of a cost function to capture several relevant aspects of the human visual system, examining a scatterplot design for some data analysis task. We show how the cost function can be used in an optimizer to search for the optimal visual design for a user's dataset and task objectives (e.g., "reliable linear correlation estimation is more important than class separation"). The approach is extensible to different analysis tasks. To test its performance in a realistic setting, we pre-calibrated it for correlation estimation, class separation, and outlier detection. The optimizer was able to produce designs that achieved a level of speed and success comparable to that of those using human-designed presets (e.g., in R or MATLAB). Case studies demonstrate that the approach can adapt a design to the data, to reveal patterns without user intervention.

  • 24. Molnos, Sonja
    et al.
    Mamdouh, Tarek
    Petri, Stefan
    Nocke, Thomas
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Coumou, Dim
    A network-based detection scheme for the jet stream core2017In: Earth System Dynamics, ISSN 2190-4979, E-ISSN 2190-4987, Vol. 8, no 1, 75-89 p.Article in journal (Refereed)
    Abstract [en]

    The polar and subtropical jet streams are strong upper-level winds with a crucial influence on weather throughout the Northern Hemisphere midlatitudes. In particular, the polar jet is located between cold arctic air to the north and warmer subtropical air to the south. Strongly meandering states therefore often lead to extreme surface weather. Some algorithms exist which can detect the 2-D (latitude and longitude) jets' core around the hemisphere, but all of them use a minimal threshold to determine the subtropical and polar jet stream. This is particularly problematic for the polar jet stream, whose wind velocities can change rapidly from very weak to very high values and vice versa. We develop a network-based scheme using Dijkstra's shortest-path algorithm to detect the polar and subtropical jet stream core. This algorithm not only considers the commonly used wind strength for core detection but also takes wind direction and climatological latitudinal position into account. Furthermore, it distinguishes between polar and subtropical jet, and between separate and merged jet states. The parameter values of the detection scheme are optimized using simulated annealing and a skill function that accounts for the zonal-mean jet stream position (Rikus, 2015). After the successful optimization process, we apply our scheme to reanalysis data covering 1979-2015 and calculate seasonal-mean probabilistic maps and trends in wind strength and position of jet streams. We present longitudinally defined probability distributions of the positions for both jets for all on the Northern Hemisphere seasons. This shows that winter is characterized by two well-separated jets over Europe and Asia (ca. 20 degrees W to 140 degrees E). In contrast, summer normally has a single merged jet over the western hemisphere but can have both merged and separated jet states in the eastern hemisphere. With this algorithm it is possible to investigate the position of the jets' cores around the hemisphere and it is therefore very suitable to analyze jet stream patterns in observations and models, enabling more advanced model-validation.

  • 25. Olbrich, S.
    et al.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Merzky, A.
    Knipp, H.
    Hege, H. -C
    Pralle, H.
    Lösungsansätze zur Visualisierung im High Performance Computing und Networking Kontext2002In: Zukunft der Netze - Die Verletzbarkeit meistern., 2002, Vol. 10, 269-279 p.Conference paper (Refereed)
    Abstract [de]

    In diesem Paper stellen wir ein Echtzeit-Szenario zur Überwachung und Steuerung von entfernt laufenden Großsimulationen vor, das auf einer Extraktion von Geometrien aus den Simulationsdaten, deren Übertragung über Hochgeschwindigkeitsnetze zu einem Client und der daraufhin erfolgenden Simulationssteuerung beruht. Wir stellen die Probleme eines solchen Szenarios dar und präsentieren Lösungen für diese Probleme. Basis dieses Papers ist das BMBF-geförderte DFN-Projekt "`Anwendungen der Teleimmersion in Weitverkehrsnetzen"' - einem Gigabit-Testbed mit Partnern in Berlin (ZIB) und Hannover (RRZN/RVS, Institut für Meteorologie und Klimatologie).

  • 26. Oulasvirta, A.
    et al.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Bachynskyi, M.
    Palmas, Gregorio
    Max Planck Institute for Informatics, Germany.
    Gestikulieren mit Stil2014In: Informatik-Spektrum, ISSN 0170-6012, Vol. 37, no 5, 449-453 p.Article in journal (Refereed)
    Abstract [en]

    Um Überanstrengungen und Ermüdungen vorzubeugen, müssen sich die Designer von neuen Nutzerschnittstellen auch über ergonomische Aspekte Gedanken machen. Hierzu kann eine Methode eingesetzt werden, bei der optisches Motion Capture und anschließende biomechanische Simulation verwendet werden. Wir erklären die Methode und beschreiben, wie wir sie im Bereich der Mensch-Computer-Interaktion einsetzen.

  • 27.
    Palmas, Gregorio
    et al.
    Max Planck Institute for Informatics.
    Bachynskyi, M.
    Oulasvirta, A.
    Seidel, H. -P
    Weinkauf, Tino
    Max Planck Institute for Informatics.
    An Edge-Bundling Layout for Interactive Parallel Coordinates2014In: Proc. IEEE PacificVis, IEEE , 2014Conference paper (Refereed)
    Abstract [en]

    Parallel Coordinates is an often used visualization method for multidimensional data sets. Its main challenges for large data sets are visual clutter and overplotting which hamper the recognition of patterns in the data. We present an edge-bundling method using density-based clustering for each dimension. This reduces clutter and provides a faster overview of clusters and trends. Moreover, it allows rendering the clustered lines using polygons, decreasing rendering time remarkably. In addition, we design interactions to support multidimensional clustering with this method. A user study shows improvements over the classic parallel coordinates plot in two user tasks: correlation estimation and subset tracing.

  • 28.
    Palmas, Gregorio
    et al.
    Max Planck Institute for Informatics, Germany.
    Bachynskyi, M.
    Oulasvirta, A.
    Seidel, H. -P
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    MovExp: A Versatile Visualization Tool for Human-Computer Interaction Studies with 3D Performance and Biomechanical Data2014In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 20, no 12, 2359-2368 p.Article in journal (Refereed)
    Abstract [en]

    In Human-Computer Interaction (HCI), experts seek to evaluate and compare the performance and ergonomics of user interfaces. Recently, a novel cost-efficient method for estimating physical ergonomics and performance has been introduced to HCI. It is based on optical motion capture and biomechanical simulation. It provides a rich source for analyzing human movements summarized in a multidimensional data set. Existing visualization tools do not sufficiently support the HCI experts in analyzing this data. We identified two shortcomings. First, appropriate visual encodings are missing particularly for the biomechanical aspects of the data. Second, the physical setup of the user interface cannot be incorporated explicitly into existing tools. We present MovExp, a versatile visualization tool that supports the evaluation of user interfaces. In particular, it can be easily adapted by the HCI experts to include the physical setup that is being evaluated, and visualize the data on top of it. Furthermore, it provides a variety of visual encodings to communicate muscular loads, movement directions, and other specifics of HCI studies that employ motion capture and biomechanical simulation. In this design study, we follow a problem-driven research approach. Based on a formalization of the visualization needs and the data structure, we formulate technical requirements for the visualization tool and present novel solutions to the analysis needs of the HCI experts. We show the utility of our tool with four case studies from the daily work of our HCI experts.

  • 29.
    Palmas, Gregorio
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Oulasvirta, Antti
    Aalto University.
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Optimization Landscapes: A Topological Approach to Understanding Permutation-based Optimization ProblemsManuscript (preprint) (Other academic)
    Abstract [en]

    Permutation-based optimization problemsare a class of NP-hard combinatorial problemsrepresenting many challenges in theory and practice.Their solution spaceconsists of all permutations $n!$of a given set of $n$ elements.Hence, for many real-world problemsthe solution spaceis too largeto even just visit every solution.The quality of a solutionis described by an objective function.A good understandingof the structures and symmetriesin this data is requiredto develop and steer heuristic algorithmsand other approaches to solving the underlying problem.We present a novel topological approachto exploring the objective functionsof permutation-based optimization problems.We infer the minima basinsand their propertiesfrom descending optimization paths.To deal with noise and general oversegmentation,we introduce an approachinspired by topological simplification of scalar fields.Based on this,we construct an edge-weighted graphapproximating the distances between basins,and visualize it using a force-directed layout,which shows the basins of local and global optimaorganized in a quasi-landscape.We show the variabilityof the solutions in a basinusing heat maps generated from permutation matrices.Our method is designed to be interactiveand read its input data as a streamfrom a simultaneously running simulation.We evaluate our method using different optimization problemsfrom both theory and practice.

  • 30.
    Palmas, Gregorio
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Space Bundling for Continuous Parallel Coordinates2016In: Eurographics Proceedings, The Eurographics Association , 2016Conference paper (Refereed)
    Abstract [en]

    Continuous Parallel Coordinates (CPC) are a visualization technique used to perform multivariate analysis of different scalar fields defined on thesame domain.While classic Parallel Coordinatesdraws a line for each sample point,a CPC visualization uses a density-based representation.An interesting possibility for the classic methodis to highlight higher-dimensional clustersusing edge bundling,where each line becomes a spline bent towards the centroid of the cluster.This often leads to expressive, illustrative visualizations.Unfortunately, bundling lines is not possible for CPC,as they are not involved in this method.In this paper,we propose a deformation of the visualization space for Continuous Parallel Coordinatesthat leads to similar results as those obtained through classic edge bundling.We achieve this by performing a curved-profile transformation in image space.The approach lends itself to a computationally lightweight GPU implementation.Furthermore, we provide intuitive interactionswith the bundled clusters.We show several examples of our technique applied to a commonly available data set.

  • 31. Peikert, R.
    et al.
    Günther, D.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Comment on "Second derivative ridges are straight lines and the implications for computing Lagrangian Coherent Structures, Physica D 2012.05.006"2013In: Physica D: Nonlinear Phenomena, ISSN 0167-2789, Vol. 242, no 1, 65-66 p.Article in journal (Refereed)
    Abstract [en]

    The finite-time Lyapunov exponent (FTLE) has become a standard tool for analyzing unsteady flow phenomena, partly since its ridges can be interpreted as Lagrangian coherent structures (LCS). While there are several definitions for ridges, a particular one called second derivative ridges has been introduced in the context of LCS, but subsequently received criticism from several researchers for being over-constrained. Among the critics are Norgard and Bremer [Physica D 2012.05.006], who suggest furthermore that the widely used definition of height ridges was a part of the definition of second derivative ridges, and that topological separatrices were ill-suited for describing ridges. We show that (a) the definitions of height ridges and second derivative ridges are not directly related, and (b) there is an interdisciplinary consensus throughout the literature that topological separatrices describe ridges. Furthermore, we provide pointers to practically feasible and numerically stable ridge extraction schemes for FTLE fields.

  • 32. Petz, C.
    et al.
    Weinkauf, Tino
    Zuse Institute Berlin, Germany.
    Streckwall, H.
    Salvatore, F.
    Noack, B. R.
    Hege, H. -C
    Vortex Structures at a Rotating Ship Propeller2006Other (Other academic)
  • 33. Rauschenbach, Uwe
    et al.
    Weinkauf, Tino
    University of Rostock, Germany.
    Schumann, Heidrun
    Interactive Focus and Context Display of Large Raster Images2000In: Proc. WSCG’2000, WSCG , 2000, 274-281 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents the RECTANGULAR FISHEYE VIEW, an interactive focus-and-context presentation technique for large raster images on mobile computers with small displays and limited processing power. Both the viewing of locally available images and the demand-driven display and transmission of remotely- stored images are supported by the technique. The underlying geometry calculations are explained, and the design decisions for supporting rapid interactive feedback are discussed. A scenario is described which demonstrates the performance of the method.

  • 34. Reininghaus, J.
    et al.
    Günther, D.
    Hotz, I.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Seidel, H. -P
    Combinatorial Gradient Fields for 2D Images with Empirically Convergent Separatrices2012Other (Other academic)
    Abstract [en]

    This paper proposes an efficient probabilistic method that computes combinatorial gradient fields for two dimensional image data. In contrast to existing algorithms, this approach yields a geometric Morse-Smale complex that converges almost surely to its continuous counterpart when the image resolution is increased. This approach is motivated using basic ideas from probability theory and builds upon an algorithm from discrete Morse theory with a strong mathematical foundation. While a formal proof is only hinted at, we do provide a thorough numerical evaluation of our method and compare it to established algorithms.

  • 35. Reininghaus, J.
    et al.
    Kasten, J.
    Weinkauf, Tino
    Max Planck Institute for Informatics, Germany.
    Hotz, I.
    Efficient Computation of Combinatorial Feature Flow Fields2012In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, Vol. 18, no 9, 1563-1573 p.Article in journal (Refereed)
    Abstract [en]

    We propose a combinatorial algorithm to track critical points of 2D time-dependent scalar fields. Existing tracking algorithms such as Feature Flow Fields apply numerical schemes utilizing derivatives of the data, which makes them prone to noise and involve a large number of computational parameters. In contrast, our method is robust against noise since it does not require derivatives, interpolation, and numerical integration. Furthermore, we propose an importance measure that combines the spatial persistence of a critical point with its temporal evolution. This leads to a time-aware feature hierarchy, which allows us to discriminate important from spurious features. Our method requires only a single, easy-to-tune computational parameter and is naturally formulated in an out-of-core fashion, which enables the analysis of large data sets. We apply our method to synthetic data and data sets from computational fluid dynamics and compare it to the stabilized continuous Feature Flow Field tracking algorithm.

  • 36. Sahner, J.
    et al.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Hege, H. -C
    Galilean Invariant Extraction and Iconic Representation of Vortex Core Lines2005In: Proc. Eurographics / IEEE VGTC Symposium on Visualization (EuroVis ’05), 2005, 151-160 p.Conference paper (Refereed)
    Abstract [en]

    While vortex region quantities are Galilean invariant, most methods for extracting vortex cores depend on the frame of reference. We present an approach to extracting vortex core lines independently of the frame of reference by extracting ridge and valley lines of Galilean invariant vortex region quantities. We discuss a generalization of this concept leading to higher dimensional features. For the visualization of extracted line features we use an iconic representation indicating their scale and extent. We apply our approach to datasets from numerical simulations and experimental measurements.

  • 37. Sahner, J.
    et al.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Teuber, N.
    Hege, H. -C
    Vortex and Strain Skeletons in Eulerian and Lagrangian Frames2007In: IEEE Transactions on Visualization and Computer Graphics, ISSN 1077-2626, E-ISSN 1941-0506, Vol. 13, no 5, 980-990 p.Article in journal (Refereed)
    Abstract [en]

    We present an approach to analyze mixing in flow fields by extracting vortex and strain features as extremal structures of derived scalar quantities that satisfy a duality property: they indicate vortical as well as high-strain (saddle-type) regions. Specifically, we consider the Okubo-Weiss criterion and the recently introduced Mz-criterion. While the first is derived from a purely Eulerian framework, the latter is based on Lagrangian considerations. In both cases high values indicate vortex activity whereas low values indicate regions of high strain. By considering the extremal features of those quantities, we define the notions of a vortex and a strain skeleton in a hierarchical manner: the collection of maximal 0D, 1D and 2D structures assemble the vortex skeleton; the minimal structures identify the strain skeleton. We extract those features using scalar field topology and apply our method to a number of steady and unsteady 3D flow fields.

  • 38.
    Saikia, Himangshu
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST). Max Planck Institute for Informatics.
    Seidel, H. -P
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST). Max Planck Institute for Informatics.
    Extended Branch Decomposition Graphs: Structural Comparison of Scalar Data2014In: Computer Graphics Forum (Proc. EuroVis), ISSN 1467-8659, Vol. 33, no 3, 41-50 p.Article in journal (Refereed)
    Abstract [en]

    We present a method to find repeating topological structures in scalar data sets. More precisely, we compare all subtrees of two merge trees against each other - in an efficient manner exploiting redundancy. This provides pair-wise distances between the topological structures defined by sub/superlevel sets, which can be exploited in several applications such as finding similar structures in the same data set, assessing periodic behavior in time-dependent data, and comparing the topology of two different data sets. To do so, we introduce a novel data structure called the extended branch decomposition graph, which is composed of the branch decompositions of all subtrees of the merge tree. Based on dynamic programming, we provide two highly efficient algorithms for computing and comparing extended branch decomposition graphs. Several applications attest to the utility of our method and its robustness against noise.

  • 39.
    Saikia, Himangshu
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Seidel, Hans-Peter
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Fast Similarity Search in Scalar Fields using Merging Histograms2015In: Topological Methods in Data Analysis and Visualization IV: Theory, Algorithms, and Applications, Springer, 2015, 121-134 p.Chapter in book (Refereed)
    Abstract [en]

    Similarity estimation in scalar fields using level set topology has attracted a lot of attention in the recent past. Most existing techniques match parts of contour or merge trees against each other by estimating a best overlap between them. Due to their combinatorial nature, these methods can be computationally expensive or prone to instabilities. In this paper, we use an inexpensive feature descriptor to compare subtrees of merge trees against each other. It is the data histogram of the voxels encompassed by a subtree. A small modification of the merge tree computation algorithm allows for obtaining these histograms very efficiently. Furthermore, the descriptor is robust against instabilities in the merge tree. The method is useful in an interactive environment, where a user can search for all structures similar to an interactively selected one. Our method is conservative in the sense that it finds all similar structures, with the rare occurrence of some false positives. We show with several examples the effectiveness, efficiency and accuracy of our method.

  • 40.
    Saikia, Himangshu
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Fast Topology-based Feature Tracking using a Directed Acyclic GraphManuscript (preprint) (Other academic)
  • 41.
    Saikia, Himangshu
    et al.
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Global Feature Tracking and Similarity Estimation in Time-Dependent Scalar Fields2017In: Computer graphics forum (Print), ISSN 0167-7055, E-ISSN 1467-8659, Vol. 36, no 3, 1-11 p.Article in journal (Refereed)
    Abstract [en]

    We present an algorithm for tracking regions in time-dependent scalar fields that uses global knowledge from all time steps for determining the tracks. The regions are defined using merge trees, thereby representing a hierarchical segmentation of the data in each time step. The similarity of regions of two consecutive time steps is measured using their volumetric overlap and a histogram difference. The main ingredient of our method is a directed acyclic graph that records all relevant similarity information as follows: the regions of all time steps are the nodes of the graph, the edges represent possible short feature tracks between consecutive time steps, and the edge weights are given by the similarity of the connected regions. We compute a feature track as the global solution of a shortest path problem in the graph. We use these results to steer the - to the best of our knowledge - first algorithm for spatio-temporal feature similarity estimation. Our algorithm works for 2D and 3D time-dependent scalar fields. We compare our results to previous work, showcase its robustness to noise, and exemplify its utility using several real-world data sets.

  • 42. Schulze, M.
    et al.
    Esturo, J. Martinez
    Günther, T.
    Rössl, C.
    Seidel, H. -P
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST). Max Planck Institute for Informatics.
    Theisel, H.
    Sets of Globally Optimal Stream Surfaces for Flow Visualization2014In: Computer Graphics Forum (Proc. EuroVis), ISSN 1467-8659, Vol. 33, no 3, 1-10 p.Article in journal (Refereed)
    Abstract [en]

    Stream surfaces are a well-studied and widely used tool for the visualization of 3D flow fields. Usually, stream surface seeding is carried out manually in time-consuming trial and error procedures. Only recently automatic selection methods were proposed. Local methods support the selection of a set of stream surfaces, but, contrary to global selection methods, they evaluate only the quality of the seeding lines but not the quality of the whole stream surfaces. Global methods, on the other hand, only support the selection of a single optimal stream surface until now. However, for certain flow fields a single stream surface is not sufficient to represent all flow features. In our work, we overcome this limitation by introducing a global selection technique for a set of stream surfaces. All selected surfaces optimize global stream surface quality measures and are guaranteed to be mutually distant, such that they can convey different flow features. Our approach is an efficient extension of the most recent global selection method for single stream surfaces. We illustrate its effectiveness on a number of analytical and simulated flow fields and analyze the quality of the results in a user study.

  • 43. Shi, K.
    et al.
    Theisel, H.
    Hauser, H.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Matkovic, K.
    Hege, H. -C
    Seidel, H. -P
    Path Line Attributes - an Information Visualization Approach to Analyzing the Dynamic Behavior of 3D Time-Dependent Flow Fields2009In: Topology-Based Methods in Visualization II / [ed] Hege, H. -C; Polthier, K.; Scheuermann, G., Springer , 2009, 75-88 p.Chapter in book (Other academic)
    Abstract [en]

    We describe an approach to visually analyzing the dynamic behavior of 3D time-dependent flow fields by considering the behavior of the path lines. At selected positions in the 4D space-time domain, we compute a number of local and global properties of path lines describing relevant features of them. The resulting multivariate data set is analyzed by applying state-of-the-art information visualization approaches in the sense of a set of linked views (scatter plots, parallel coordinates, etc.) with interactive brushing and focus+context visualization. The selected path lines with certain properties are integrated and visualized as colored 3D curves. This approach allows an interactive exploration of intricate 4D flow structures. We apply our method to a number of flow data sets and describe how path line attributes are used for describing characteristic features of these flows.

  • 44. Shi, K.
    et al.
    Theisel, H.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Hauser, H.
    Hege, H. -C
    Seidel, H. -P
    Extracting Separation Surfaces of Path Line Oriented Topology in Periodic 2D Time-Dependent Vector Fields2007In: Journal of WSCG, ISSN 1213-6964, Vol. 15, no 1, 75-82 p.Article in journal (Refereed)
    Abstract [en]

    This paper presents an approach to extracting the separation surfaces from periodic 2D time-dependent vector fields based on a recently introduced path line oriented topology. This topology is based on critical path lines which repeat the same spatial cycle per time period. Around those path lines there are areas of similar asymptotic flow behavior basins which are captured by a 2D Poincare map as a discrete dynamical system. Due to pseudo discontinuities in this map and the discrete integration scheme, separatrices between the basins can not be obtained as integral curves. Instead we choose a point-wise approach to segment the Poincare map and apply computer vision algorithms to extract the 2D separation curves. Starting from those curves we integrate separation surfaces which partition the periodic 2D time-dependent vector field into areas of similar path line behavior. We apply our approach to a number of data sets to to demonstrate its utility.

  • 45. Shi, K.
    et al.
    Theisel, H.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Hauser, H.
    Hege, H. -C
    Seidel, H. -P
    Path Line Oriented Topology for Periodic 2D Time-Dependent Vector Fields2006In: Proc. Eurographics / IEEE VGTC Symposium on Visualization (EuroVis ’06), 2006, 139-146 p.Conference paper (Refereed)
    Abstract [en]

    This paper presents an approach to extracting a path line oriented topological segmentation for periodic 2D time-dependent vector fields. Topological methods aiming in capturing the asymptotic behavior of path lines rarely exist because path lines are usually only defined over a fixed time-interval, making statements about their asymptotic behavior impossible. For the data class of periodic vector fields, this restriction does not apply any more. Our approach detects critical path lines as well as basins from which the path lines converge to the critical ones. We demonstrate our approach on a number of test data sets.

  • 46. Shi, K.
    et al.
    Theisel, H.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Hege, H. -C
    Seidel, H. -P
    Finite-Time Transport Structures of Flow Fields2008In: Proc. IEEE Pacific Visualization 2008, IEEE Computer Society, 2008, 63-70 p.Conference paper (Refereed)
    Abstract [en]

    Modern experimental and computational fluid mechanics are increasingly concerned with the structure nature of fluid motion. Recent research has highlighted the analysis of one transport structure which is called Lagrangian coherent structure. However, the quantity nature of the flow transport is still unclear. In this paper, we focus on the transport characteristics of physical quantities and propose an approach to visualize the finite-time transport structure of quantity advection. This is similar to an integral convolution over a scalar field along path-lines of a flow field. Applied to a well chosen set of physical quantity fields this yields structures giving insights into the dynamical processes of the underlying flow. We demonstrate our approach on a number of test data sets.

  • 47. Shi, K.
    et al.
    Theisel, H.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Hege, H. -C
    Seidel, H. -P
    Visualizing Transport Structures of Time-Dependent Flow Fields2008In: IEEE Computer Graphics and Applications, ISSN 0272-1716, E-ISSN 1558-1756, Vol. 28, no 5, 24-36 p.Article in journal (Refereed)
    Abstract [en]

    This article focuses on the transport characteristics of physical properties in fluids - in particular, visualizing the finite-time transport structure of property advection. Applied to a well-chosen set of property fields, the proposed approach yields structures giving insights into the underlying flow’s dynamic processes.

  • 48. Stöter, T.
    et al.
    Weinkauf, Tino
    KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST). Max Planck Institute for Informatics.
    Seidel, H. -P
    Theisel, H.
    Implicit Integral Surfaces2012In: Proc. Vision, Modeling and Visualization, 2012, 127-134 p.Conference paper (Refereed)
    Abstract [en]

    We present an implicit method for globally computing all four classic types of integral surfaces – stream, path, streak, and time surfaces – in 3D time-dependent vector fields. Our novel formulation is based on the representation of a time surface as implicit isosurface of a 3D scalar function advected by the flow field. The evolution of a time surface is then given as an isovolume in 4D space-time spanned by a series of advected scalar functions. Based on this, the other three integral surfaces are described as the intersection of two isovolumes derived from different scalar functions. Our method uses a dense flow integration to compute integral surfaces globally in the entire domain. This allows to change the seeding structure efficiently by simply defining new isovalues. We propose two rendering methods that exploit the implicit nature of our integral surfaces: 4D raycasting, and projection into a 3D volume. Furthermore, we present a marching cubes inspired surface extraction method to convert the implicit surface representation to an explicit triangle mesh. In contrast to previous approaches for implicit stream surfaces, our method allows for multiple voxel intersections, covers all regions of the flow field, and provides full control over the seeding line within the entire domain.

  • 49. Theisel, H.
    et al.
    Rï¿œssl, C.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Morphological Representations of Vector Fields2008In: Shape Analysis and Structuring / [ed] Floriani, L.; Spagnuolo, M., Springer , 2008Chapter in book (Other academic)
    Abstract [en]

    This chapter gives an overview on topological methods for vector field processing. After introducing topological features for 2D and 3D vector fields, we discuss how to extract and use them as visualization tools for complex flow phenomena. We do so both for static and dynamic fields. Finally, we introduce further applications of topological methods for compressing, simplifying, comparing, and constructing vector fields.

  • 50. Theisel, H.
    et al.
    Sahner, J.
    Weinkauf, Tino
    Zuse Institute Berlin.
    Hege, H. -C
    Seidel, H. -P
    Extraction of Parallel Vector Surfaces in 3D Time-Dependent Fields and Application to Vortex Core Line Tracking2005In: Proc. IEEE Visualization 2005, 2005, 631-638 p.Conference paper (Refereed)
    Abstract [en]

    We introduce an approach to tracking vortex core lines in time-dependent 3D flow fields which are defined by the parallel vectors approach. They build surface structures in the 4D space-time domain. To extract them, we introduce two 4D vector fields which act as feature flow fields, i.e. their integration gives the vortex core structures. As part of this approach, we extract and classify local bifurcations of vortex core lines in space-time. Based on a 4D stream surface integration, we provide an algorithm to extract the complete vortex core structure. We apply our technique to a number of test data sets.

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