Alexander Wiebel

Hochschule Worms · Department of Computer Science

We present a method to extract and visualize vortices that originate from bounding walls of three-dimensional time-dependent flows. These vortices can be detected using their footprint on the boundary, which consists of critical points in the wall shear stress vector field. In order to follow these critical points and detect their transformations,...

Stream surfaces are an intuitive approach to represent 3D vector fields. In many cases, however, they are challenging objects to visualize and to understand, due to a high degree of self-occlusion. Despite the need for adequate rendering methods, little work has been done so far in this important research area. In this paper, we present an illustra...

In the last years a variety of open-source software packages focusing on visualization of human brain data have evolved. Many of them are designed to be used in a pure academic environment and are optimized for certain tasks or special data. The open source visualization system we introduce here is called OpenWalnut. It is designed and developed to...

Scientists, engineers and physicians are used to analyze 3D data with slice-based visualizations. Radiologists for example are trained to read slices of medical imaging data. Despite the numerous examples of sophisticated 3D rendering techniques, domain experts, who still prefer slice-based visualization do not consider these to be very useful. Sin...

We discuss the concept of directness in the context of spatial interaction with visualization. In particular, we propose a model that allows practitioners to analyze and describe the spatial directness of interaction techniques, ultimately to be able to better understand interaction issues that may affect usability. To reach these goals, we disting...

In this work, we propose a visual analytics system to analyze deep reinforcement learning (deepRL) models working on the track reconstruction of charged particles in the field of particle physics. The data of these charged particles are in the form of point clouds with high-dimensional features. We use one of the existing post hoc saliency methods...

Objective. Gradient-based optimization using algorithmic derivatives can be a useful technique to improve engineering designs with respect to a computer-implemented objective function. Likewise, uncertainty quantification through computer simulations can be carried out by means of derivatives of the computer simulation. However, the effectiveness o...

Objective. Proton therapy is highly sensitive to range uncertainties due to the nature of the dose deposition of charged particles. To ensure treatment quality, range verification methods can be used to verify that the individual spots in a pencil beam scanning treatment fraction match the treatment plan. This study introduces a novel metric for pr...

The application of augmented reality in nature and in the context of environmental education is not common. Moreover, augmented reality is often used mainly for visualization, which puts the user in a rather passive state. To promote a more active user experience, we have created an interactive AR environment for outdoor scenarios. In this article,...

The Bergen proton Computed Tomography (pCT) is a prototype detector under construction. It aims to have the capability to track and measure ions’ energy deposition to minimize uncertainty in proton treatment planning. It is a high granularity digital tracking calorimeter, where the first two layers will act as tracking layers to obtain positional i...

When learning a motor skill it is helpful to get corrective feedback from an instructor. This will support the learner to execute the movement correctly. With modern technology, it is possible to provide this feedback via mixed reality. In most cases, this involves visual cues to help the user understand the corrective feedback. We analyzed recent...

Algorithmic derivatives can be useful to quantify uncertainties and optimize parameters using computer simulations. Whether they actually are, depends on how "well-linearizable" the program is. Proton computed tomography (pCT) is a medical imaging technology with the potential to increase the spatial accuracy of the dose delivered in proton-beam ra...

The implementation of augmented reality in nature and in an environmental education context, is not a common case. Furthermore, augmented reality is often used basically for visualization, which puts users in a rather passive state. In this paper we investigate how near and far interaction using a head-mounted-display can be combined with visualiza...

Background Proton computed tomography (pCT) and radiography (pRad) are proposed modalities for improved treatment plan accuracy and in situ treatment validation in proton therapy. The pCT system of the Bergen pCT collaboration is able to handle very high particle intensities by means of track reconstruction. However, incorrectly reconstructed and s...

Augmented, virtual and mixed reality (AR/VR/MR) are technologies of great potential due to the engaging and enriching experiences they are capable of providing. However, the possibilities that AR/VR/MR offer in the area of environmental applications are not yet widely explored. In this paper we present the outcome of a survey meant to discover and...

In this paper we propose augmented reality (AR) modes for showing virtual tree roots in the nature. The main question that we want to answer is “How is it possible to convincingly represent virtual 3D models of tree roots as being located in the forest soil, underground, while using the AR technology?”. We present different rendering and occlusion...

Augmented, virtual and mixed reality (AR/VR/MR) are technologies of great potential due to the engaging and enriching experiences they are capable of providing. However, the possibilities that AR/VR/MR offer in the area of environmental applications are not yet widely explored. In this paper we present the outcome of a survey meant to discover and...

Die gegenwärtig stattfindende Durchdringung aller menschlichen Lebensbereiche mit digitalen Technologien bringt für die Veranstaltungsbranche sowohl Chancen als auch Herausforderungen mit sich (vgl. Zanger 2019, S. 13ff.). Dabei geht die Markteinführung digitaler Technologien gemäß des sog. Hype-Zyklus der Unternehmensberatung Gartner in der Praxis...

Augmented reality (AR), virtual reality (VR) and mixed reality (MR) are technologies of great potential due to the engaging and enriching experiences they are capable of providing. Their use is rapidly increasing in diverse fields such as medicine, manufacturing or entertainment. However, the possibilities that AR, VR and MR offer in the area of en...

Paper on combination of spatial VR and 360 video.<br

Paper on combination of spatial VR and 360 video.<br

In diesem Kapitel wird der Einsatz von Augmented Reality (AR) in Lehrveranstaltungen an Hochschulen diskutiert. Als Fallbeispiel wird ein Konzept betrachtet, welches die Bereiche Blended Learning und Augmented Reality verbindet. Anders als in der klassischen Definition von Blended Learning wird hier aber Digitales in der Präsenzphase eingesetzt. Da...

This paper discusses the use of augmented reality in a university course in audiovisual production. An active learning approach is used and the students are fulfilling tasks with the help of augmented reality technology (here the HoloLens glasses). The developed augmented reality application connects topics of the lecture like film planning, storyb...

Smartphones und die darauf installierten Softwareapplikationen (Apps) können im Kontext von Veranstaltungen verschiedenen Anspruchsgruppen einen Mehrwert stiften. Veranstaltern bieten sie die Möglichkeit, ihr Leistungsspektrum mit einer eigenen Veranstaltungs-App zu erweitern, indem sie beispielsweise den Gästen einen schnellen Zugang zu veranstalt...

We present a vector field approximation for two-dimensional vector fields that preserves their topology and significantly reduces the memory footprint. This approximation is based on a segmentation. The flow within each segmentation region is approximated by an affine linear function. The implementation is driven by four aims: (1) the approximation...

Tutorial at IEEE VIS 2015 Conference

Tutorial at Eurographics Conference 2015

Natural sciences, medicine and engineering are only a small selection of application domains where volumetric data, continuous as well as scattered, are close to ubiquitous. While the visualization of such data itself is not straightforward, interaction with and manipulation of volumetric data - essential aspects of effective data analysis - pose e...

In this chapter we summarize the top research challenges in creating successful visualization tools for tensor fields in engineering. The analysis is based on our collective experiences and on discussions with both domain experts and visualization practitioners. We find that creating visualization tools for engineering tensors often involves solvin...

In this paper we present an interactive system that integrates the visual analysis of nerve fiber pathway approximations from diffusion tensor imaging (DTI) with electroencephalography (EEG) data. The technique uses source reconstructions from EEG data to define certain regions of interest in the brain. These regions, in turn, are used to selective...

An intuitive and sparse representation of the void space of porous materials supports the efficient analysis and visualization of interesting qualitative and quantitative parameters of such materials. We introduce definitions of the elements of this void space, here called pore space, based on its distance function, and present methods to extract t...

Linear approximation plays an important role in many areas employing numerical algorithms. Particularly in the field of vector field visualization, it is the basis of widely used techniques. In this paper, we introduce two methods to extract areas in two- and three-dimensional vector fields that are connected to linear flow behavior. We propose a r...

Trajectory visualization is an important tool to capture intrinsic characteristics of vector fields. However, often this class of geometric visualization suffers from visual clutter due to the number of curves that occlude each other and may cover relevant features. Attempts trying to avoid this effect often require complex pre/post-processing for...

Glyphs are a widespread technique to depict local properties of different kinds of fields. In this paper we present a new glyph for singularities in non-linear vector fields. We do not simply show the properties of the derivative at the singularities as most previous methods do, but instead illustrate the behavior that goes beyond the local linear...

In this paper, we present two combinatorial methods to process 3-D steady vector fields, which both use graph algorithms to extract features from the underlying vector field. Combinatorial approaches are known to be less sensitive to noise than extracting individual trajectories. Both of the methods are a straightforward extension of an existing 2-...

The grading of inflammatory bowel disease (IBD) severity is important to determine the proper treatment strategy and to quantify the response to treatment. Traditionally, ileocolonoscopy is considered the reference standard for assessment of IBD. However, the procedure is invasive and requires extensive bowel preparation. Magnetic resonance imaging...

One of the most promising avenues for compiling anatomical brain connectivity data arises from diffusion magnetic resonance imaging (dMRI). dMRI provides a rather novel family of medical imaging techniques with broad application in clinical as well as basic neu-roscience as it offers an estimate of the brain's fiber structure completely non-invasiv...

Diffusion magnetic resonance imaging is so far the only medical imaging modality that has the potential for probing anatomical brain connectivity in vivo. Specifically, it provides the data basis for a set of techniques allowing for tracking of fiber bundles in the brain's white matter. Furthermore, due to the micro-structural basis of the diffusio...

In this paper we applyvector field topology methods to amathematical model for the fluid dynamics of reaggregation processes in tissue engineering. The experimental background are dispersed embryonic retinal cells, which reaggregate in a rotation culture on a gyratory shaker, according to defined rotation and culture conditions. Under optimal condi...

Graph averaging as a means to compare multichannel EEG coherence networks

We present an algorithm that allows stream surfaces to recognize and adapt to vector field topology. Standard stream surface algorithms either refine the surface uncontrolled near critical points which slows down the computation considerably and may lead to a poor surface approximation. Alternatively, the concerned region is omitted from the stream...

Diffusion tensor images and higher-order diffusion images are the foundation for neuroscience researchers who are trying to gain insight into the connectome, the wiring scheme of the brain. Although modern imaging devices allow even more detailed anatomical measurements, these pure anatomical connections are not sufficient for understanding how the...

We introduce an improved algorithm for streak line approximation in 2D and 3D time-dependent vector fields. The algorithm is mainly based on iterative refinement of an initial coarse approximation of the streak line. The refinement process is steered by a predicate indicating the local approximation quality. We apply the algorithm to several real-w...

In the last years, a variety of open-source software packages focusing on visualization of human brain data have evolved. Many of them are designed to be used in a pure academic environment and are optimized for certain tasks or special data. The open source visualization system we introduce here is called OpenWalnut. It is designed and developed t...

The study of flow separation from walls or solid objects is still an active research area in the fluid dynamics and flow visualization communities and many open questions remain. This paper aims at introducing a new method for the extraction of separation manifolds originating from separation lines. We address the problem from the flow visualizatio...

We introduce a novel technique for the construction of smooth stream surfaces of 4th order precision. While common stream surface techniques use linear interpolation for generating seed points for new streamlines in the refinement phase, we use Hermite interpolation. The derivatives needed for Hermite interpolation are obtained by integration along...

Understanding fluid flow data, especially vortices, is still a challenging task. Sophisticated visualization tools help to gain insight. In this paper, we present a novel approach for the interactive comparison of scalar fields using isosurfaces, and its application to fluid flow datasets. Features in two scalar fields are defined by largest contou...

The present thesis focuses on the visualization of vector fields with an emphasis on flow fields. In connection with a DFG project, close collaboration and discussions with fluid dynamicists raised new questions concerning the detection and depiction of special features in flows. The contributions of the thesis in this context are the following: Fi...

The notions of Finite-Time Lyapunov Exponent (FTLE) and Lagrangian Coherent Structures provide a strong framework for the analysis and visualization of complex technical flows. Their definition is simple and intuitive, and they are built on a deep theoretical foundation. We apply these concepts to enable the analysis of flows in the immediate vicin...

In this paper, we present an overview of a number of existing flow visualization methods, developed by the authors in the recent past, that are specifically aimed at integrating and leveraging domain-specific knowledge into the visualization process. These methods transcend the traditional divide between interactive exploration and featurebased sch...

Modern unsteady (multi-)field visualizations require an effective reduction of the data to be displayed. From a huge amount of information the most informative parts have to be extracted. Instead of the fuzzy application dependent notion of feature, a new approach based on information theoretic concepts is introduced in this paper to detect importa...

Modern unsteady (multi-)field visualizations require an effective reduction of the data to be displayed. From a huge amount of information the most informative parts have to be extracted. Instead of the fuzzy application dependent notion of feature, a new approach based on information theoretic concepts is introduced in this paper to detect importa...

Using topology for feature analysis in flow fields faces several problems. First of all, not all features can be detected using topology based methods. Second, while in flow feature analysis the user is interested in a quantification of feature parameters like position, size, shape, radial velocity and other parameters of feature models, many of th...

We present, extend, and apply a method to extract the contribution of a subregion of a data set to the global flow. To isolate this contribution, we decompose the flow in the subregion into a potential flow that is induced by the original flow on the boundary and a localized flow. The localized flow is obtained by subtracting the potential flow fro...

This work is an attempt to test the concept of the hydrodynamic charge (analogous to the electric charge in electromagnetism) in the simple case of a coherent structure such as the Burgers vortex. We provide experimental measurements of both the so-called Lamb vector and its divergence (the charge) by two-dimensional particles images velocimetry. I...

Visualizing flow structures according to the users' interests provides insight to scientists and engineers. In previous work, a flow structure based on streamline predicates, that examine, whether a streamline has a given property, was defined. Evaluating all streamlines results in characteristic sets grouping all streamlines with similar behavior...

It is a challenging task to visualize the behavior of time-dependent 3D vector fields. Most of the time an overview of unsteady fields is provided via animations, but, unfortunately, animations provide only transient impressions of momentary flow. In this paper we present two approaches to visualize time varying fields with fixed geometry. Path lin...

In this paper we present an approach to the analysis of the contribution of a small subregion in a dataset to the global flow. To this purpose, we subtract the potential flow that is induced by the boundary of the sub-domain from the original flow. Since the potential flow is free of both divergence and rotation, the localized flow field retains th...