SemSeg

The thorough analysis of flows plays an important role in many different processes, such as airplane and car design, environmental research, and medicine. Scientific Visualization and its subfield flow visualization have provided a variety of techniques for the domain experts to visually analyze large and complex flow data sets. Among them, so-called topology-based methods play an important role. Vector field topology (VFT) is a mathematically rigorous theory that reveals the essential structure of a static vector field. However, this approach is only fully valid for static vector fields.

Recent developments in the target domains of this project show a clear transition from steady to unsteady flow scenarios. Accordingly, we have to see that the traditionally proven approaches do not apply any more and that a conceptual change in the methodology of visual analysis is necessary. Topology-based methods which account for the complete dynamic behaviour of flow fields are strongly needed but do not exist. Steps toward this goal have been done from several sides, delivering promising but yet only partial results.

It is the objective of this project to research a new segmentation method for unsteady flows that has the elegance and specificity of (steady) VFT, but which provides correct results for unsteady flows as well. This project aims at the formulation of a sound theoretical mechanism to describe structural features in time-dependent flow. Similar to the case of steady flow, were topology has proven its usefulness in many years, it is straight-forward to expect that the new approach will also establish its important role in the analysis and discussion of time-dependent flow scenarios. As part of a successful project, concrete algorithms to extract and visualize the topological structures are derived from the new mechanism. Implementations of them will allow studying the usefulness on a number of real-life flow data from different areas of application.

Research Partners

  • University of Bergen, Norway (UiB)
  • University of Magdeburg, Germany (UMAG)
  • ETH Zurich, Switzerland (ETH)
  • VRVis Research Center in Vienna, Austria (VRVis)

Link(s)

Publications

2012

    [Bibtex]
    @MISC {Brambilla12SemSegWorkshop,
    author = "Andrea Brambilla and Robert Carnecky",
    title = "Introduction to Illustrative Flow Visualization",
    howpublished = "Presentation at the 3rd SemSeg User Forum Workshop",
    month = "February",
    year = "2012",
    images = "images/Brambilla12Illustrative.png",
    thumbnails = "images/Brambilla12Illustrative_thumb.png",
    location = "Magdeburg, Germany",
    url = "http://vc.cs.ovgu.de/index.php?article_id=232",
    pres = "pdfs/Brambilla12SemSegWorkshop.pdf",
    project = "semseg"
    }
    [PDF] [Bibtex]
    @ARTICLE {Brambilla12AHierarchical,
    author = "Andrea Brambilla and Ivan Viola and Helwig Hauser",
    title = "A Hierarchical Splitting Scheme to Reveal Insight into Highly Self-Occluded Integral Surfaces",
    journal = "Journal of WSCG",
    year = "2012",
    volume = "20",
    number = "1",
    pages = "57--64",
    month = "July",
    abstract = "In flow visualization, integral surfaces are of particular interest for their ability to describe trajectories of massless particles. In areas of swirling motion, integral surfaces can become very complex and difficult to understand. Taking inspiration from traditional illustration techniques, such as cut-aways and exploded views, we propose a surface analysis tool based on surface splitting and focus+context visualization. Our surface splitting scheme is hierarchical and at every level of the hierarchy the best cut is chosen according to a surface complexity metric. In order to make the interpretation of the resulting pieces straightforward, cuts are always made along isocurves of specific flow attributes. Moreover, a degree of interest can be specified, so that the splitting procedure attempts to unveil the occluded interesting areas. Through practical examples, we show that our approach is able to overcome the lack of understanding originating from structural occlusion.",
    pdf = "pdfs/Brambilla12AHierarchical.pdf",
    images = "images/Brambilla12AHierarchical01.png, images/Brambilla12AHierarchical02.png, images/Brambilla12AHierarchical03.png",
    thumbnails = "images/Brambilla12AHierarchical01_thumb.png, images/Brambilla12AHierarchical02_thumb.png, images/Brambilla12AHierarchical03_thumb.png",
    issn = "1213-6972",
    publisher = "Union Agency",
    url = "http://wscg.zcu.cz/JWSCG/",
    event = "WSCG 2012 - 20th International Conference on Computer Graphics, Visualization and Computer Vision",
    location = "Pilsen, Czech Republic",
    pres = "pdfs/Brambilla12AHierarchical.pptx",
    project = "semseg"
    }
    [Bibtex]
    @MISC {Hauser12SemSegWorkshop,
    author = "Helwig Hauser and Kresimir Matkovic",
    title = "Interactive Visual Analysis of Time-Dependent Flows",
    howpublished = "Presentation at the 3rd SemSeg User Forum Workshop",
    month = "February",
    year = "2012",
    images = "images/Hauser12SemSegWorkshop.png",
    thumbnails = "images/Hauser12SemSegWorkshop_thumb.png",
    location = "Magdeburg, Germany",
    url = "http://vc.cs.ovgu.de/index.php?article_id=232",
    pres = "pdfs/Hauser12SemSegWorkshop-pres.pdf",
    project = "semseg"
    }
    [PDF] [DOI] [Bibtex]
    @INPROCEEDINGS {Brambilla12Illustrative,
    author = "Andrea Brambilla and Robert Carnecky and Ronald Peikert and Ivan Viola and Helwig Hauser",
    title = "Illustrative Flow Visualization: State of the Art, Trends and Challenges",
    booktitle = "EuroGraphics 2012 State of the Art Reports (STARs)",
    year = "2012",
    pages = "75--94",
    abstract = "Flow visualization is a well established branch of scientific visualization and it currently represents an invaluable resource to many fields, like automotive design, meteorology and medical imaging. Thanks to the capabilities of modern hardware, flow datasets are increasing in size and complexity, and traditional flow visualization techniques need to be updated and improved in order to deal with the upcoming challenges. A fairly recent trend to enhance the expressiveness of scientific visualization is to produce depictions of physical phenomena taking inspiration from traditional handcrafted illustrations: this approach is known as illustrative visualization, and it is getting a foothold in flow visualization as well. In this state of the art report we give an overview of the existing illustrative techniques for flow visualization, we highlight which problems have been solved and which issues still need further investigation, and, finally, we provide remarks and insights on the current trends in illustrative flow visualization.",
    pdf = "pdfs/Brambilla12Illustrative.pdf",
    images = "images/Brambilla12Illustrative.png",
    thumbnails = "images/Brambilla12Illustrative_thumb.png",
    url = "http://diglib.eg.org/EG/DL/conf/EG2012/stars/075-094.pdf",
    doi = "10.2312/conf/EG2012/stars/075-094",
    location = "Cagliari, Italy",
    pres = "pdfs/Brambilla12Illustrative.pptx",
    project = "semseg"
    }
    [PDF] [DOI] [Bibtex]
    @INPROCEEDINGS {Pobitzer12Filtering,
    author = "Armin Pobitzer and Ronald Peikert and Raphael Fuchs and Holger Theisel and Helwig Hauser",
    title = "Filtering of FTLE for Visualizing Spatial Separation in Unsteady 3D Flow",
    booktitle = "Topological Methods in Data Analysis and Visualization II",
    year = "2012",
    editor = "R. Peikert and H. Hauser and H. Carr and R. Fuchs",
    pages = "237--253",
    publisher = "Springer",
    abstract = "Texture mapping is a common method for combining surface geometry with image data, with the resulting photorealistic 3D models being suitable not only for visualisation purposes but also for interpretation and spatial measurement, in many application fields, such as cultural heritage and the earth sciences. When acquiring images for creation of photorealistic models, it is usual to collect more data than is finally necessary for the texturing process. Images may be collected from multiple locations, sometimes with different cameras or lens configurations and large amounts of overlap may exist. Consequently, much redundancy may be present, requiring sorting to choose the most suitable images to texture the model triangles. This paper presents a framework for visualization and analysis of the geometric relations between triangles of the terrain model and covering image sets. The application provides decision support for selection of an image subset optimized for 3D model texturing purposes, for non-specialists. It aims to improve the communication of geometrical dependencies between model triangles and the available digital images, through the use of static and interactive information visualisation methods. The tool was used for computer-aided selection of image subsets optimized for texturing of 3D geological outcrop models. The resulting textured models were of high quality and with a minimum of missing texture, and the time spent in time-consuming reprocessing was reduced. Anecdotal evidence indicated that an increased user confidence in the final textured model quality and completeness makes the framework highly beneficial. ",
    pdf = "pdfs/Pobitzer12Filtering.pdf",
    images = "images/Pobitzer12Filtering01.png, images/Pobitzer12Filtering02.png",
    thumbnails = "images/Pobitzer12Filtering01_thumb.png, images/Pobitzer12Filtering02_thumb.png",
    doi = "http://dx.doi.org/10.1007/978-3-642-23175-9_16",
    url = "http://dx.doi.org/10.1007/978-3-642-23175-9_16",
    project = "semseg"
    }

2011

    [Bibtex]
    @INPROCEEDINGS {lez11pathlines,
    author = "Alan Lez and Andreas Zajic and Kresimir Matkovic and Armin Pobitzer and Michael Mayer and Helwig Hauser",
    title = "Interactive Exploration and Analysis of Pathlines in Flow Data",
    booktitle = "Proc. International Conference in Central Europe on ComputerGraphics, Visualization and Computer Vision (WSCG 2011)",
    year = "2011",
    pages = "17--24",
    abstract = "The rapid development of large-scale scientific computing nowadays allows to inherently respect the unsteady character of natural phenomena in computational flow simulation. With this new trend to more regularly consider time-dependent flow scenarios, an according new need for advanced exploration and analysis solutions emerges. In this paper, we now present three new concepts in pathline analysis which further improve the abilities of analysis: a multi-step analysis which helps to save time and space needed for computation, direct pathline brushing, and usage of pre-configured view arrangements. We have found that clever combining of these three concepts with already existing methods creates very powerful tool for pathline analysis. The coordinated multiple views (CMV) tool used supports iterative composite brushing which enables a quick information drill-down. We illustrate the usefulness using an example from the automotive industry. We have analyzed an exhaust manifoldtime-dependent simulation data set.",
    images = "images/lez11pathlines1.jpg, images/lez11pathlines2.jpg",
    thumbnails = "images/lez11pathlines1_thumb.jpg, images/lez11pathlines2_thumb.jpg",
    location = "Plzen, Czech Republic",
    project = "semseg"
    }
    [Bibtex]
    @INPROCEEDINGS {pobitzer11semseg,
    author = "Armin Pobitzer and Helwig Hauser",
    title = "The {SemSeg} project and recent developments in flow visualization",
    booktitle = "Proc. Sixth National Conference on Computational Mechanics (MekIT'11)",
    year = "2011",
    pages = "281--292",
    address = "Trondheim, Norway",
    month = "May",
    publisher = "Tapir Academic Press",
    abstract = "The present paper discusses recent efforts to develop semantic segmentation of spacetime flow domains for visualization purposes, taking thework of the SemSeg project as a starting point. In particular we address separation structures based on Finite-time Lyapunov exponents and their extraction, the incorporation of uncertainty, and the application of Interactive Visual Analysis in the context of flow visualization.",
    images = "images/pobitzer11semseg.jpg",
    thumbnails = "images/pobitzer11semseg_thumb.jpg",
    editors = "B. Skallerud and H.I. Andersson",
    project = "semseg"
    }
    [Bibtex]
    @ARTICLE {pobitzer11energyScale,
    author = "Armin Pobitzer and Murat Tutkun and {\O }yvind Andreassen and Raphael Fuchs and Ronald Peikert and Helwig Hauser",
    title = "Energy-scale Aware Feature Extraction for Flow Visualization",
    journal = "Computer Graphics Forum",
    year = "2011",
    volume = "30",
    number = "3",
    pages = "771--780",
    abstract = "In the visualization of flow simulation data, feature detectors often tend to result in overly rich response, making some sort of filtering or simplification necessary to convey meaningful images. In this paper we present an approach that builds upon a decomposition of the flow field according to dynamical importance of different scales of motion energy. Focusing on the high-energy scales leads to a reduction of the flow field while retaining the underlying physical process. The presented method acknowledges the intrinsic structures of the flow according to its energy and therefore allows to focus on the energetically most interesting aspects of the flow. Our analysis shows that this approach can be used for methods based on both local feature extraction and particle integration and we provide a discussion of the error caused by the approximation. Finally, we illustrate the use of the proposed approach for both a local and a global feature detector and in the context of numerical flow simulations.",
    images = "images/pobitzer11energyScale1.jpg, images/pobitzer11energyScale3.jpg, images/pobitzer11energyScale2.jpg",
    thumbnails = "images/pobitzer11energyScale1_thumb.jpg, images/pobitzer11energyScale3_thumb.jpg, images/pobitzer11energyScale2_thumb.jpg",
    url = "http://dx.doi.org/10.1111/j.1467-8659.2011.01926.x",
    event = "EuroVis 2011",
    location = "Bergen, Norway",
    project = "semseg"
    }
    [Bibtex]
    @ARTICLE {pobitzer11topology,
    author = "Armin Pobitzer and Ronald Peikert and Raphael Fuchs and Benjamin Schindler and Alexander Kuhn and Holger Theisel and Kresimir Matkovic and Helwig Hauser",
    title = "The State of the Art in Topology-based Visualization of Unsteady Flow",
    journal = "Computer Graphics Forum",
    year = "2011",
    volume = "30",
    number = "6",
    pages = "1789--1811",
    month = "September",
    abstract = "Vector fields are a common concept for the representation of many different kinds of flow phenomena in science and engineering. Methods based on vector field topology are known for their convenience for visualizing and analyzing steady flows, but a counterpart for unsteady flows is still missing. However, a lot of good and relevant work aiming at such a solution is available.We give an overview of previous research leading towards topology-based and topology-inspired visualization of unsteady flow, pointing out the different approaches and methodologies involved as well as their relation to each other, taking classical (i.e., steady) vector field topology as our starting point. Particularly, we focus on Lagrangian methods, space-time domain approaches, local methods, and stochastic and multi-field approaches. Furthermore, we illustrate our review with practical examples for the different approaches.",
    images = "images/pobitzer10topology.jpg,",
    thumbnails = "images/pobitzer10topology_thumb.jpg",
    project = "semseg",
    url = "http://dx.doi.org/10.1111/j.1467-8659.2011.01901.x"
    }

2010

    [Bibtex]
    @INPROCEEDINGS {pobitzer10topology,
    author = "Armin Pobitzer and Ronald Peikert and Raphael Fuchs and Benjamin Schindler and Alexander Kuhn and Holger Theisel and Kresimir Matkovic and Helwig Hauser",
    title = "On the Way Towards Topology-Based Visualization of Unsteady Flow - the State of the Art",
    booktitle = "EuroGraphics 2010 State of the Art Reports (STARs)",
    year = "2010",
    pages = "137--154",
    abstract = "Vector fields are a common concept for the representation of many different kinds of flow phenomena in science and engineering. Topology-based methods have shown their convenience for visualizing and analyzing steady flow but a counterpart for unsteady flow is still missing. However, a lot of good and relevant work has been done aiming at such a solution.We give an overview of the research done on the way towards topology-based visualization of unsteady flow, pointing out the different approaches and methodologies involved as well as their relation to each other, takingclassical (i.e. steady) vector field topology as our starting point. Particularly, we focus on Lagrangian Methods, Space-Time Domain Approaches, Local Methods, and Stochastic and Multi-Field Approaches. Furthermore, weillustrated our review with practical examples for the different approaches.",
    images = "images/pobitzer10topology.jpg,",
    thumbnails = "images/pobitzer10topology_thumb.jpg",
    event = "EuroGraphics 2010",
    location = "Norrk{\"o}ping, Sweden",
    pres = "pdfs/pobitzer10topology-presentation.pdf",
    project = "semseg"
    }
    [Bibtex]
    @ARTICLE {fuchs10lagrangian,
    author = "Raphael Fuchs and Jan Kemmler and Benjamin Schindler and Jrgen Waser and Filip Sadlo and Helwig Hauser and Ronald Peikert",
    title = "Toward a Lagrangian Vector Field Topology",
    journal = "Computer Graphics Forum",
    year = "2010",
    volume = "29",
    number = "3",
    pages = "1163--1172",
    month = "june",
    abstract = "In this paper we present an extended critical point concept which allows us to apply vector field topology in the case of unsteady flow. We propose a measure for unsteadiness which describes the rate of change of the velocities ina fluid element over time. This measure allows us to select particles for which topological properties remain intact inside a finite spatio-temporal neighborhood. One benefit of this approach is that the classification of critical points based on the eigenvalues of the Jacobian remains meaningful. In the steady case the proposed criterion reduces to the classical definition of critical points. As a first step we show that finding an optimal Galilean frame of reference can be obtained implicitly by analyzing the acceleration field. In a second step we show that this can be extended by switching to the Lagrangian frame of reference. This way the criterion can detect critical points moving along intricate trajectories. We analyze the behavior of the proposed criterion based on two analytical vector fields for which a correct solution is defined by their inherent symmetries and present results for numerical vector fields.",
    images = "images/fuchs10lagrangian2.jpg, images/fuchs10lagrangian.jpg",
    thumbnails = "images/fuchs10lagrangian2_thumb.jpg, images/fuchs10lagrangian_thumb.jpg",
    event = "EuroVis 2010",
    location = "Bordeaux, France",
    url = "http://dx.doi.org/10.1111/j.1467-8659.2009.01686.x",
    project = "semseg"
    }