VMV11

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https://diglib.eg.org/handle/10.2312/1015

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Seamless Integration of Multimodal Shader Compositing into a Flexible Ray Casting Pipeline
(The Eurographics Association, 2011) Arens, Stephan; Bolte, Matthias; Domik, Gitta; Peter Eisert and Joachim Hornegger and Konrad Polthier
In the last three years a number of multi-volume GPU ray casting systems have been presented. Some of them are very powerful and provide a wide variety of features. However, these approaches are either only capable of displaying multiple modalities together without logically combining them or they lack the necessary flexibility for rapid visual development. These features are fundamental for visualizing the coherent information of multimodal data. In this paper we therefore present an integrated way of visually specifying a volume rendering pipeline including a flexible multimodal compositing of sampling, transfer functions, logical operators and shading. As a result the data flow can be visually constructed and retraced from preprocessing through to the shader operations. Hence intuitive visual prototyping of multimodal transfer function compositing is possible at runtime.
Is it Necessary to Model the Matrix Degrading Enzymes for Simulating Tumour Growth?
(The Eurographics Association, 2011) Toma, Alina; Mang, Andreas; Schütz, Tina A.; Becker, Stefan; Buzug, Thorsten M.; Peter Eisert and Joachim Hornegger and Konrad Polthier
We propose a hybrid continuum discrete model to simulate tumour growth on a microscopic scale. The lattice based spatio temporal model consists of reaction diffusion equations that describe interactions between cancer cells and their microenvironment. The components that are typically considered are usually nutrients, like oxygen and glucose, matrix degrading enzymes (MDE) and the extracellular matrix (ECM). The in vivo processes are very complex and occur on different levels. This in turn leads to huge computational costs. Thus, the aim is to describe the processes on the basis of simplified mathematical approaches, which depict realistic results at the same time. In this work we discuss if we have to model the MDEs or if the ECM can be modelled directly depending on the cancer cells distribution. Comparing the results for modelling the tumour growth with the common choice and with the simplified model without MDE, we observe almost similar results. The model without MDE allows for a straightforward, fast and accurate implementation.
Auto-Tilt Photography
(The Eurographics Association, 2011) Sadlo, Filip; Dachsbacher, Carsten; Peter Eisert and Joachim Hornegger and Konrad Polthier
Tilt-shift camera lenses are a powerful artistic tool to achieve effects like selective focus with very shallow depth of field. Typically they are used by professional photographers only, which is due to the high cost and weight, and the intricate, non-intuitive handling. We introduce the auto-tilt mechanism which is as easy to use as the standard autofocus. It allows automatic sharp focus of objects not parallel to the image plane, such as in landscape photography where getting everything sharp is often desirable. In contrast to pure computational approaches that are based on resampling from focal stacks, our approach based on true exposures enables time-dependent scenes and higher image quality. Auto-tilt can also be controlled via a simple sketching user-interface letting the photographer quickly define image regions inside and outside sharp focus. We demonstrate auto-tilt using a simple rapidly prototyped experimental setup that tilts the sensor (as opposed to classic tilt-shift lenses), and describe possible implementations in off-the-shelf cameras. We also outline future prospects with flexible image sensors currently being developed.
Probabilistic Inverse Dynamics for Blood Pattern Reconstruction
(The Eurographics Association, 2011) Cecchetto, Benjamin T.; Heidrich, Wolfgang; Peter Eisert and Joachim Hornegger and Konrad Polthier
We present a method of reconstructing the region of origin and trajectories for particles given impact directions and positions. This method works for nonlinear trajectories, such as parabolic motion or motion with drag if given drag parameters. Our method works if given the impact speeds as well, or they can be estimated using a similar total initial energy prior. We apply our algorithm to the case of forensic blood pattern reconstruction, by automatically estimating impact velocities directly form the blood patterns. We validate our method in physically accurate simulated experiments, a feasibility study varying the impact angle and speed to estimate the impact speed from blood drop densities, as well as a forensic experiment using blood to reconstruct the region of origin.
A Clustering-based Visualization Technique to Emphasize Meaningful Regions of Vector Fields
(The Eurographics Association, 2011) Kuhn, Alexander; Lehmann, Dirk J.; Gaststeiger, Rocco; Neugebauer, Matthias; Preim, Bernhard; Theisel, Holger; Peter Eisert and Joachim Hornegger and Konrad Polthier
This paper proposes a vector field visualization approach that extracts and visualizes grouped regions of static 3D vector fields of similar curvature behavior. These regions are argued to ease the recognition of regions of potential interest and accelerate the general exploration process of vector fields. Our approach detects regions of similar geometric stream properties such as integral curvature and visualizes them by means of compact cluster boundaries. To supplement existing approaches our method combines information on relevant scales to extract meaningful semantical aspects of the overall field structure. For proof of concept we illustrate our results based on real and synthetic data sets.
RITK: The Range Imaging Toolkit - A Framework for 3-D Range Image Stream Processing
(The Eurographics Association, 2011) Wasza, Jakob; Bauer, Sebastian; Haase, Sven; Schmid, Moritz; Reichert, Sebastian; Hornegger, Joachim; Peter Eisert and Joachim Hornegger and Konrad Polthier
The recent introduction of low-cost devices for real-time acquisition of dense 3-D range imaging (RI) streams has attracted a great deal of attention. However, to date, there exists no open source framework that is explicitly dedicated to real-time processing of RI streams. In this paper, we present the Range Imaging Toolkit (RITK). The goal is to provide a powerful yet intuitive software platform that facilitates the development of range image stream applications. RITK puts emphasis on real-time processing of range image streams and proposes the use of a dedicated pipeline mechanism. Furthermore, we introduce a powerful and convenient interface for range image processing on the graphics processing unit (GPU). Being designed thoroughly and in a generic manner, the toolkit is able to cope with the broad diversity of data streams provided by available RI devices and can easily be extended by custom range imaging sensors or processing modules. RITK is an open source project and will be made publicly available at http://www5.cs.fau.de/ritk.
Measuring BRDFs of Immersed Materials
(The Eurographics Association, 2011) Berger, Kai; Reshetouski, Ilya; Magnor, Marcus; Ihrke, Ivo; Peter Eisert and Joachim Hornegger and Konrad Polthier
We investigate the effect of immersing real-world materials into media of different refractive indices. We show, that only some materials follow the Fresnel-governed behaviour. In reality, many materials exhibit unexpected effects such as stronger localized highlights or a significant increase in the glossy reflection due to microgeometry. In this paper, we propose a new measurement technique that allows for measuring the BRDFs of materials that are immersed into different media.
Real-time Rendering of Stack-based Terrains
(The Eurographics Association, 2011) Löffler, Falko; Müller, Andreas; Schumann, Heidrun; Peter Eisert and Joachim Hornegger and Konrad Polthier
Usually, terrain rendering relies on a 2D regular grid of height values, the so called height field. Height fields describe 2.5D surfaces and are not able to present complex 3D terrain features. In contrast, a 3D data representation quickly exceeds the available memory resources. To overcome this problem we apply material stacks. Material stacks combine the simplicity of 2D height fields and the extended modeling capabilities of 3D volumetric data. However, this approach requires expensive rendering and is difficult to realize in real-time. In this paper we present an innovative real-time rendering approach of terrains relying on material stacks. Our approach is based on two major steps: First, a LoD hierarchy for material-stacks is generated. Second, during rendering a multi-staged quadrangulation pipeline extracts terrain surface from the material stacks. As a result, we achieve real-time frame rates at high resolutions.
Extracting Flow Structures Using Sparse Particles
(The Eurographics Association, 2011) Agranovsky, Alexy; Garth, Christoph; Joy, Kenneth I.; Peter Eisert and Joachim Hornegger and Konrad Polthier
In recent years, Lagrangian Coherent Structures (LCS) have been characterized using the Finite-Time Lyapunov Exponent, following the advection of a dense set of particles into a corresponding flow field. The large amount of particles needed to sufficiently map a flow field has been a non-trivial computational burden in the application of LCS. By seeding a minimal amount of particles into the flow field, Moving Least Squares, combined with FTLE, will extrapolate the important feature locations at which further refinement is desired. Following the refinement procedure, MLS produces a continuous function reconstruction allowing the characterization of Lagrangian Coherent Structures with a lower number of particles. Through multiple data sets, we show that given a sparse and refined sampling, MLS will reproduce FTLE fields exhibiting a nominal error while maintaining a performance increase when compared to the standard, dense finite difference approach.
AVDT - Automatic Visualization of Descriptive Texts
(The Eurographics Association, 2011) Spika, Christian; Schwarz, Katharina; Dammertz, Holger; Lensch, Hendrik P. A.; Peter Eisert and Joachim Hornegger and Konrad Polthier
Expressing mental images visually as 3D scenes is a time-consuming challenge. Therefore, we employ natural language to facilitate the creation of virtual environments. In this paper, we present a framework, which automatically converts an arbitrary descriptive text into a representative 3D scene. Our system parses a user-written input text, extracts information using techniques from Natural Language Processing (NLP) and identifies relevant units. Based on derived object-to-object relations, our system associates every object with an appropriate 3D model and evaluates spatial dependencies of the entities. The resulting locations are combined based on adequate heuristics in order to create natural looking virtual environments. Finally, a physics engine is used to render a realistic and interactive 3D scene which enables the user to actively manipulate the stage setup.
Instant Level-of-Detail
(The Eurographics Association, 2011) Grund, Nico; Derzapf, Evgenij; Guthe, Michael; Peter Eisert and Joachim Hornegger and Konrad Polthier
Highly detailed models are commonly used in computer games and other interactive rendering applications. In this context, static levels-of-detail are frequently used to achieve real-time frame rates. While this is a simple solution to improve the rendering performance, the additional geometry needs to be stored and loaded into graphics memory. This is especially problematic in online applications, where the data needs to be transmitted over a possibly slow connection. On the other hand, consumer level computers are usually equipped with a graphics card that can be used for general purpose parallel computing. Based on this observation, we propose a high-quality parallel mesh simplification algorithm based on the quadric error metric. The simplification performance can compete with the time required to load additional meshes from a local hard disk.
Data-Driven Visualization of Functional Brain Regions from Resting State fMRI Data
(The Eurographics Association, 2011) Crippa, Alessandro; Roerdink, Jos B.T.M.; Peter Eisert and Joachim Hornegger and Konrad Polthier
Functional parcellation of the human cortex plays an important role in the understanding of brain functions. Tradi- tionally, functional areas are defined according to anatomical landmarks. Recently, new techniques were proposed that do not require a priori segmentation of the cortex. Such methods allow functional parcellation by functional information alone. We propose here a data-driven approach for the exploration of functional connectivity of the cortex. The method extends a known parcellation method, used in multichannel EEG analysis, to define and extract functional units (FUs), i.e., spatially connected brain regions that record highly correlated fMRI signals. We apply the method to the study of fMRI data and provide a visualization, inspired by the EEG case, that uses linked views to facilitate the understanding of both the location and the functional similarity of brain regions. Initial feedback on our approach was received from four domain experts, researchers in the field of neuroscience.
Simulating Deep Sea Underwater Images Using Physical Models for Light Attenuation, Scattering, and Refraction
(The Eurographics Association, 2011) Sedlazeck, Anne; Koch, Reinhard; Peter Eisert and Joachim Hornegger and Konrad Polthier
When adapting computer vision algorithms to underwater imaging, two major differences in image formation occur. While still traveling through the water, light rays are scattered and absorbed depending on their wavelength, creating the typical blue hue and low contrast in underwater images. When entering the underwater housing of the camera, light rays are refracted twice upon passing from water into glass and into air. We propose a simulator for both effects based on physical models for deep sea underwater images captured by cameras in underwater housings with glass port thicknesses in the order of centimeters. Hence, modeling refraction by explicitly computing the correct path of the rays allows to accurately simulate distortions induced by underwater housings. The Jaffe- McGlamery model for effects on color is often used in computer vision algorithms as a base for simplification. We extend this model to incorporate color images, shadows, and several light sources.
Surface Flow from Visual Cues
(The Eurographics Association, 2011) Petit, Benjamin; Letouzey, Antoine; Boyer, Edmond; Franco, Jean-Sébastien; Peter Eisert and Joachim Hornegger and Konrad Polthier
In this paper we study the estimation of dense, instantaneous 3D motion fields over a non-rigidly moving surface observed by multi-camera systems. The motivation arises from multi-camera applications that require motion information, for arbitrary subjects, in order to perform tasks such as surface tracking or segmentation. To this aim, we present a novel framework that allows to efficiently compute dense 3D displacement fields using low level visual cues and geometric constraints. The main contribution is a unified framework that combines flow constraints for small displacements with temporal feature constraints for large displacements and fuses them over the surface using local rigidity constraints. The resulting linear optimization problem allows for variational solutions and fast implementations. Experiments conducted on synthetic and real data demonstrate the respective roles of flow and feature constraints as well as their ability to provide robust surface motion cues when combined.
Bent Normals and Cones in Screen-space
(The Eurographics Association, 2011) Klehm, Oliver; Ritschel, Tobias; Eisemann, Elmar; Seidel, Hans-Peter; Peter Eisert and Joachim Hornegger and Konrad Polthier
Ambient occlusion (AO) is a popular technique for real-time as well as offline rendering. One of its benefits is a gain in efficiency due to the fact that occlusion and shading are decoupled which results in an average occlusion that modulates the surface shading. Its main drawback is a loss of realism due to the lack of directional occlusion and lighting. As a solution, the use of bent normals was proposed for offline rendering. This work describes how to compute bent normals and bent cones in combination with screen-space ambient occlusion. These extensions combine the speed and simplicity of AO with physically more plausible lighting.
Koiter's Thin Shells on Catmull-Clark Limit Surfaces
(The Eurographics Association, 2011) Wawrzinek, Anna; Hildebrandt, Klaus; Polthier, Konrad; Peter Eisert and Joachim Hornegger and Konrad Polthier
We present a discretization of Koiter's model of elastic thin shells based on a finite element that employs limit surfaces of Catmull Clark's subdivision scheme. The discretization can directly be applied to control grids of Catmull Clark subdivision surfaces, and, therefore, integrates modeling of Catmull Clark subdivision surfaces with analysis and optimization of elastic thin shells. To test the discretization, we apply it to standard examples for physical simulation of thin shells and compute free vibration modes of thin shells. Furthermore, we use the discrete shell model to set up a deformation-based modeling system for Catmull Clark subdivision surfaces. This system integrates modeling of subdivision surfaces with deformation-based modeling and allows to switch back and forth between the two different approaches to modeling.
Interactive Exploration of Polymer-Solvent Interactions
(The Eurographics Association, 2011) Thomaß, Bertram; Walter, Jonathan; Krone, Michael; Hasse, Hans; Ertl, Thomas; Peter Eisert and Joachim Hornegger and Konrad Polthier
The interaction of three-dimensional linked hydrophilic polymers with surrounding solvents in time-dependent data sets is of great interest for domain experts and current research in molecular dynamics. These polymers are called hydrogels, and their most characteristic property is their swelling in aqueous solutions by absorbing the solvent. Their conformation transition can be studied by investigations of the interaction of the single polymer strand and the solvent directly around the polymer at an atomistic level. We present new visualization techniques to interactively study time-dependent data sets from molecular dynamics simulations-with special regard to polymer-solvent interactions like local concentrations and hydrogen bonds-as well as filtering methods to facilitate analysis. Such methods that visualize polymer-solvent interactions on a hydration shell around a polymer are not available in current tools and can greatly facilitate the visual analysis, which helps domain experts to extract additional information about hydrogel characteristics and gain new insights from the simulation results. While our visual analysis methods presented in this paper clearly facilitate the analysis of hydrogels and lead to new insight, the presented concepts are applicable to other domains like proteins or polymers in general that interact with solvents.
Adaptive Level-of-Precision for GPU-Rendering
(The Eurographics Association, 2011) Meyer, Quirin; Sussner, Gerd; Greiner, Günter; Stamminger, Marc; Peter Eisert and Joachim Hornegger and Konrad Polthier
Video memory is a valuable resource that has grown much slower than the rendering power of GPUs over the last years. Today, video memory is often the limiting factor in interactive high-quality rendering applications. The most often used solution to reduce memory consumption is to apply level-of-detail (LOD) methods: only a simplified version of the mesh with less vertices and triangles is kept in memory. In this paper we examine a simple orthogonal compression approach that is mostly neglected: adapting the level-of-precision (LOP) of vertex data. The main idea is to quantize vertex positions according to the current view distance, and adapt precision by adding or removing single bit planes. We provide an analysis of the resulting image error, and show that visual artifacts can be avoided by simply constraining the quantization for critical vertices. Our approach allows both random access on vertex data as well as quickly switching between LOP. In experiments we found that our approach compresses vertex positions by about 70percent on average without loss in rendering performance or image quality.
Improving Stability and Compactness in Street Layout Visualizations
(The Eurographics Association, 2011) Kratt, Julian; Strobelt, Hendrik; Deussen, Oliver; Peter Eisert and Joachim Hornegger and Konrad Polthier
We present and evaluate improvements for Street Layout, a technique that can be used for visualizing evolving hierarchical data such as file structures or software systems. Street Layouts represent data as street networks, where each street represents a branch of the hierarchy and buildings around streets represent leaves. We extended the initial idea in various ways to increase compactness and visual stability. Our approaches are compared against the current methods in a conducted technical evaluation. A prototypic application shows the applicability of our improvements for visualizing a real world data set.
Partial Symmetry Detection in Volume Data
(The Eurographics Association, 2011) Kerber, Jens; Wand, Michael; Krüger, Jens; Seidel, Hans-Peter; Peter Eisert and Joachim Hornegger and Konrad Polthier
In this paper, we present an algorithm for detecting partial Euclidean symmetries in volume data. Our algorithm finds subsets in voxel data that map to each other approximately under translations, rotations, and reflections. We implement the search for partial symmetries efficiently and robustly using a feature-based approach: We first reduce the volume to salient line features and then create transformation candidates from matching only local configurations of these line networks. Afterwards, only a shortlist of transformation candidates need to be verified using expensive dense volume matching. We apply our technique on both synthetic test scenes as well as real CT scans and show that we can recover a large amount of partial symmetries for complexly structured volume data sets.

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