Kolloquiumszyklus - previous dates

Few scientific topics catch as much attention as climate research these days. Will temperatures rise significantly in the upcoming decades? Will snow and ice covers disappear? Will draugths and severe storms threaten lifes all around the globe? Many questions like these move people, politics, and also business. To give as good as possible answers, climate researchers employ most modern measurement, simulation, and analysis methodology, resulting in challenging compilations of data of heterogeneous form and origin, usually with multi- ple variates, and almost always time-dependent. Accordingly, visualization is challenged and advanced approaches are needed to enable effective exploration, analysis and presen- tation. In this talk recent research work on how to support hypothesis generation in climate research through interactive visual exploration is presented. A discussion of associated challenges explains why visualization of data from climate research clearly has the potential to initiate interesting future research in visualization.

The video game industry is the only entertainment industry that has seen steady, double digit growth over the past fifteen years even out doing the high tech industry.
This provides many opportunities for talented individuals who may not have thought about making games as a career.
Wolfgang Hamann (Pres/CEO - Koolhaus Games, Vancouver, Canada) will be providing an overview of this fascinating field as well as discussing the Game Development Process - the marriage of software development, game design, art and sound

3D datasets are becoming increasingly large and complex. In medicine, fiber structures within the brain are inferred from diffusion-tensor magnetic resonance imaging (DT-MRI), yielding thousands to millions of curved trajectories. In chemistry, billions of atoms are included in large-scale molecular dynamics simulations. In both cases, the resulting geometry becomes difficult to comprehend in part because of its complexity.
We describe two approaches to improving perception of the resulting 3D scenes. The first approach is to apply physically based illumination rather than the conventional "local" illumination. The second approach is to transform the data into an ensemble coordinate system where geometric complexity increases slowly. The utility of these approaches have been validated by performing user studies.

In 2005 the university hospital of Maastricht (Netherlands) acquired a Medtronic N20 Polestar, a mobile, low-field, intraoperative MRI scanner which can be used in a standard operating room. To make better use of this scanner and enhance its images with high-quality preoperative imaging data the hospital started a close collaboration with the biomedical image analysis group of the technical university of Eindhoven (prof. Bart ter Haar Romeny). The goal is to define research projects related to image-guided neurosurgery that involve preoperative imaging, intraoperative MRI or a combination of both. For this purpose, the image-guided neurosurgery group was founded in 2007. This group is directly located at the university hospital of Maastricht and therefore at only a minute's distance from the neurosurgeons, one of whom (a resident) is a part-time but active member of this group working on his own PhD. This KV presentation will discuss the image-guided neurosurgery group and some of its past and current projects. Special attention will be given to deep brain stimulation and multimodal visualization, the latter of which was a master's thesis project of the presenter Ralph Brecheisen. His own PhD project in the image-guided neurosurgery group has only recently started and is still ill-defined but will focus on visualization for neurosurgery applications. The main purpose of his visit to Vienna is to find ideas for research and opportunities for collaboration, possibly in combination with the university hospital of Maastricht.

High-fidelity real-time visualization of surfaces under high-dynamic-range (HDR) image-based illumination provides an invaluable resource for various computer graphics applications. Material design, lighting design, architectural previsualization, and gaming are just a few such applications.
We present filtered importance sampling, a technique for image-based lighting of glossy objects using BRDF importance sampling in conjunction with environment map filtering. Furthermore, we extend the algorithm with real-time shadow computation. Free from any pre-computation, the algorithm supports fully dynamic scenes and, above all, is simple to implement.

The goal of computerized image generation is to convey information to the user or viewer, whether for artistic reflection, scientific discovery, or decision making. The history of art, design, illustration, and perception form a rich basis for developing interactive computerized visual environments for discovery, engineering, and analytical decision making. The development of interactive visualization techniques to effectively, rapidly and accurately convey information can fundamentally change the pace of scientific discovery and adoption of new science into usable applications. Moreover, integrated data management, analysis, and interactive visual environments provide insight and information from the massive data generated by computer simulations, sensors, and web-based sources. The potential of these integrated environments has led to a evolution of visualization to visual analytics.
In this talk, I'll discuss the role that computer graphics and interactive integrated visualization and analytics can play in research, discovery, and deployment in a variety of application areas. We have been developing integrated visual analytics environments for a diverse set of applications from homeland security to fundamental computational science. I'll describe some of our integrated visualization, data management, and analytical solutions for weather forecasting, cloud modeling, surgical training, computational nanoelectronics, computational fluid dynamics, cancer care engineering, syndromic surveillance, agricultural food production, and emergency response.

Point counting is a technique used for estimate the composition of a sample. We developed an interactive application designed to facilitate the point counting process through visual computing; this application could be useful in any domain in which the sample image can be digitized. Additionally, we provide other visual analysis tools showing how the application can benefit from the combination of these concepts and the techniques coming from Information Visualization. We utilize the point counting technique on petrographic thin section images in order to perform modal analyses of rocks, but it could be used on many other types of samples in order to estimate their composition.

With the recent advancements in biomedical imaging technology, molecular processes in the cell can now be brought directly in relation to structural and functional changes at higher levels. Functional imaging (optical, nuclear and MR with targeted contrast agents) provides a window on cellular biochemistry and gene expression, while structural imaging (CT, MR, ultrasound) may be used to measure the resulting structural changes in the whole body. Disease processes and treatment effects can now be followed over time, from molecule to organism, both in pre-clinical small animal models and in humans.
For a single time point, a molecular imaging study may consist of photographs, photon emission images, serial CT, MR or PET slices, functional MR imaging, MR spectroscopy, and histology. We have recently started working on new visualization techniques that will enable the in-depth visual exploration of relations between disease evolution, underlying molecular processes and structural and functional changes that are locked up in combined molecular, functional and structural imaging data.
This talk starts with a brief overview of the TU Delft Medical Visualisation group and its research activities. I will then introduce molecular imaging and the role of visualisation in this new field, after which I will present our latest results on a visualisation system for bioluminescence imaging and on whole-body articulated registration for small animal imaging.

In this talk we show how biased methods based on density estimation of photon hits such as photon maps can be extended. Instead of using photon hits as in photon maps and combining them with final gathering we exploit the photon paths in two ways. First, we make density estimation in ray space of photon paths, which reduces bias. Second, we reverse the process of density estimation and splat energy of photons around the cones of photon paths. We show the results and timings of the image synthesis based on the two new methods and the differences to traditional photon mapping.

The appearance of real-world objects depends on the incident illumination, on the 3D geometry of the object, and on the reflection properties of the object's surfaces. Reflectance fields capture the resulting global light transport in such a way that the object can be relit in arbitrary virtual environments faithfully reproducing the appearance of the original. In this talk I will present an overview about our current work on acquiring and processing reflectance fields. One part will cover acquisition techniques that are able to measure the global light transport within a scene on a ray-to-ray basis allowing for capturing and reproducing effects such as subsurface scattering, refractions and caustics. One remaining problem is that reflectance fields are typically acquired only for a discrete set of incident light directions. A rotation in the incident illumination is likely to produce artifacts due to this coarse sampling. In the second part I therefore will address the problem of upsampling reflectance fields in the light domain allowing for smoothly moving shadows and highlights when light sources move around the scene.

The traditional development of virtual and augmented reality applications usually relied on expensive workstation hardware and custom developed software. Today, this approach seems not reasonable anymore. Alone the development of a modern rendering pipeline for the application can consume several man-months. However, modern game engines incorporate modern and highly efficient rendering pipelines that could support the application development on higher levels. This talk introduces important terms and definitions, presents some examples like the adoption with spatially immersive projector-based displays (SIDs) and shows some problems that are inherent to game engines.

Functional approximation of scattered data is a popular technique for compactly representing various types of datasets in computer graphics, including surface, volume, and vector datasets. Typically, sums of Gaussians or similar radial basis functions are used in the functional approximation and PC graphics hardware is used to quickly evaluate and render these datasets. While truncated radially symmetric basis functions are quick to evaluate and simple for encoding optimization, they are not the most appropriate choice for data that is not radially symmetric and are especially problematic for representing linear, planar, and many non-spherical structures. Therefore, the functional approximation system is extended to using more general basis functions, such as ellipsoidal basis functions(EBFs) that provide greater compression and visually more accurate encodings of volumetric scattered datasets. In addition to static data approximation, temporal data is encoded using results from encoding previous timestep to speed the encoding time. Moreover, as a part of visual analytics, we developed tools for zoonotic syndromic surveillance, linked animal and human visual analytics for healthcare surveillance, network visualization, etc. In this talk, We will introduce these visual analytics tools and discuss their applications.

SOFA is a new open source framework primarily targeted at medical simulation research. Based on an advanced software architecture, it allows to (1)~create complex and evolving simulations by combining new algorithms with algorithms already included in SOFA; (2) modify most parameters of the simulation~--~deformable behavior, surface representation, solver, constraints, collision algorithm, etc.~--~by simply editing an XML file; (3) build complex models from simpler ones using a scene-graph description; (4) efficiently simulate the dynamics of interacting objects using abstract equation solvers; and (5) reuse and easily compare a variety of available methods. In this paper we highlight the key concepts of the SOFA architecture and illustrate its potential through a series of examples.

Curved Planar Reformation (CPR) has proved to be a practical and widely used tool for the visualization of curved tubular structures within the human body. It has been useful in medical procedures involving the examination of blood vessels and the spine. However, it is more difficult to use it for large, tubular, structures such as the trachea and the colon because abnormalities may be smaller relative to the size of the structure and may not have such distinct density and shape characteristics.
Our new approach (which we call 'Volumetric CPR') improves on this situation by using volume rendering for hollow regions and standard CPR for the surrounding tissue. This effectively combines gray scale contextual information with detailed color information from the area of interest. The approach is successfully used with each of the standard CPR types and the resulting images are promising as an alternative to virtual flythroughs.
We show that lighting is non-trivial because of the deformation which occurs when the three dimensional curved tubular structure is mapped to a two dimensional image plane. We show how lighting and shading is computed in this scenario and how it can be used to maximize the users understanding of the surface.
Lastly, we demonstrate that our new approach is a useful tool for displaying additional information not typically available during a flythrough, such as real-time surface coverage data or translucency rendering. We also show that, because the Volumetric CPR provides and alternative view on the colon, it increases surface coverage from 86.8% (for a flythrough in each direction) to 99.2%; significantly improving the chances of detecting abnormalities.

ET is a powerful tool for visualization of the highly dynamic structures of organelles in living cells. Although investigation using transmission electron microscopy requires fixed and embedded material which is stable in high vacuum and under a high voltage electron beam, the modern preparation method of high pressure fixation (HPF) allows obtaining snapshots from the arrangement of organelles in living cells in relation to a particular experimental condition.
In order to obtain appropriate 3D data, tilt series from semithin sections (200-300 nm), cut in parallel to the plane of the monolayer of cell cultures, are performed using a Tecnai-20 200KV transmission electron microscope (FEI, Eindhoven, The Netherlands) equipped with an eucentric goniometer. In addition a rotation holder (Gatan, Inc., Pleasanton, USA) is used for orientation of rod-like structures parallel to the tilt axis and also for dual axis acquisition. Series of tilted images (range: -70° to +70°) are acquired with a tilt increment of 1°. After holder calibration, dislocations in x, y and z axis are corrected by the Explore 3D acquisition software (FEI). The volume of the semithin sections is reconstructed by the back projection method into serial slices using the software package Inspect 3D (FEI). This software implicates also an alignment tool using cross correlation which is prerequisite for an appropriate reconstruction. Dual axis reconstruction requires acquisition of perpendicular orientated tilt series. It is performed using the Matlab software platform and an advanced version of the "Tomo Toolbox", kindly provided by Dr. Jürgen Plitzko, Dept. of Molecular Structural Biology (Head: Prof. Dr. Wolfgang Baumeister), Max Planck Institute of Biochemistry in Martinsried near Munich.
3D models are performed by tracing the structures of interest in every slice with colored contours that are merged in the Z axis by the help of the Amira 3.0 software (Mercury Computer Systems, Merignac Cedex, France). Models, generated in this way can be rotated in the space and presented as movie.
The aim of this presentation is to introduce interesting applications from cell biology and to discuss problems and limitations in 3D visualization using the commercial software as described above.

QuteMol is an open source (GPL), interactive, /high quality molecular visualization system/. It exploits the current GPU capabilites through OpenGL shaders to offer an array of innovative visual effects. QuteMol visualization techniques are aimed at improving clarity and an easier understanding of the 3D shape and structure of large molecules or complex proteins.
In this talk, the individual techniques implemented in QuteMol are presented. These include:

• Real Time Ambient Occlusion
• Depth Aware Silhouette Enhancement
• Ball and Sticks, Space-Fill and Liquorice visualization modes
• High resolution antialiased snapshots for creating publication quality renderings
• Automatic generation of animated gifs of rotating molecules for web pages animations
• Interactive rendering of large molecules and protein (>100k atoms)
• Standard PDB input

Swirl and tumble motion are two important, common fluid flow patterns from computational fluid dynamics (CFD) simulations typical of automotive engine simulation. We study and visualize swirl and tumble flow using several advanced flow visualization techniques: direct, geometric, texture-based, and feature-based. When illustrating these methods, we describe the relative strengths and weaknesses of each approach across multiple spatlo-temporal domains typical of an engineer's analysis. The result is the most comprehensive, systematic search for swirl and tumble motion ever performed. Based on this investigation we offer perspectives on where and when these techniques are best applied in order to visualize the behavior of swirl and tumble motion.

This presentation introduces myself and explains briefly which are my research activities

Image compositing is combining two or more images by overlaying them. For this to be meaningful, some of the image areas need to be less than perfectly opaque, so the rearmost images can be seen. When Porter and Duff wrote their 1984 paper on Image Compositing, they used a four channel colour model (r,g,b,a). The extra channel, called alpha, represented the opacity of the colour (r,g,b). We have recently shown that this is mathematically a projective space, which extends the range of use of the alpha colour model, including to applications beyond compositing. This published work will be described. We also have some very recent unpublished results and these too will be presented.

We present a coherent hierarchical level of detail (HLOD) culling algorithm that employs a novel metric to perform the refinement of a HLOD-based system that takes into account visibility information. The information is gathered from the result of a hardware occlusion query (HOQ) performed on the bounding volume of a given node in the hierarchy. Although the advantages of doing this are clear, previous approaches treat refinement criteria and HOQ as independent subjects. For this reason, HOQs have been used restrictively as if their result were boolean. In contrast to that, we fully exploit the results of the queries to be able to take into account visibility information within refinement conditions. We do this by interpreting the result of a given HOQ as the virtual resolution of a screen space where the refinement decision takes place. In order to be able to use our proposed metric to perform the refinement of the HLOD hierarchy as well as to schedule HOQs, we exploit the spatial and temporal coherence inherent to hierarchical representations. Despite the simplicity of our approach, in our experiments we obtained a substantial performance boost (compared to previous approaches) in the frame-rate with minimal loss in image quality.

In this talk we investigate the effects of function composition in the form g(f(x)) = h(x) by means of a spectral analysis of h. We decompose the spectral description of h(x) into a scalar product of the spectral description of g(x) and a term that solely depends on f(x) and that is independent of g(x). We then use the method of stationary phase to derive the essential maximum frequency of g(f(x)) bounding the main portion of the energy of its spectrum. This limit is the product of the maximum frequency of g(x) and the maximum derivative of f(x). This leads to a proper sampling of the composition h of the two functions g and f. We apply our theoretical results to a fundamental open problem in volume rendering -- the proper sampling of the rendering integral after the application of a transfer function.

Fully 3D datasets have become ubiquitous in a wide range of disciplines, such as science, engineering, medicine, and even entertainment. There is a vast demand to efficiently create these data, as well as fuse, relate, and visualize them. In this talk I will report on our efforts in all of these domains. First I will discuss techniques that utilize GPUs for rapid tomographic volume reconstruction and even direct volume visualization from X-ray projection data. Then I will describe our Magic Volume Lens framework which fuses and augments different types of volumetric data at different scales into one composite representation, providing a variety of zoom lenses for focus+context GPU-accelerated viewing with semantic context.

Today the generation of raw 3D models has become quite easy. Typical sources for geometric data are: 3D scanning, CAD system output, reconstructions from images and video and so on. However, while these models usually have a sufficient quality at the first glance, the removal of inconsistencies and other optimizations are still necessary to make these raw models any useful for downstream applications beyond mere display. Besides this basic mesh repair, one would also like to convert unstructured polygonal models into meshes where individual faces are of high quality in terms of aspect ratio and the degrees of freedom (i.e. vertices) are aligned to major geometric features. These are the global and the local aspects of remeshing techniques respectively. In my talk I will present a number of mesh repair and mesh optimization techniques which are numerically robust and sufficiently efficient to process large dataset of realistic input quality.

In this talk I will describe approaches towards user-oriented exploration of volumetric datasets. A visualization technique is presented, which allows to emphasize certain regions of interest by applying different visual appearances interactively. In order to give better insights into this regions occluding parts can be removed or visualized differently such that a better focussing is allowed. Since when applying these strategies the overall structure of the dataset is modified, spatial comprehension may become more difficult. To diminish this effect a visualization technique to support depth perception is proposed.