VMV: Vision, Modeling, and Visualization

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Analysis of Vortex Merge Graphs
(The Eurographics Association, 2012) Kasten, Jens; Zoufahl, Andre; Hege, Hans-Christian; Hotz, Ingrid; Michael Goesele and Thorsten Grosch and Holger Theisel and Klaus Toennies and Bernhard Preim
We propose an analysis framework to investigate different flow quantities such as vorticity, λ<sub>2</sub> or the acceleration magnitude along vortex merge graphs and within their regions of influence. The explicit extraction of vortex merge graphs enables the application of statistical tools to investigate the vortex core lines themselves. The analysis tool provides common plots as scatter plots and parallel coordinates to explore the correlation of different quantities. An abstract representation of the vortex merge graph highlights birth, death and merges of vortices. Interactive picking of substructures supports a closer insepection of single vortices and their evolution. A further step integrates the regions of influence into the statistical analysis. Minima, maxima, median, mean and other percentiles of the measures along the vortex merge graph and its regions are visualized. The usability of the framework is demonstrated using a simulated flow data set of a mixing layer and a jet.
Audio Resynthesis on the Dancefloor: A Music Structural Approach
(The Eurographics Association, 2013) Tauscher, Jan-Philipp; Wenger, Stephan; Magnor, Marcus; Michael Bronstein and Jean Favre and Kai Hormann
We propose a method for synthesizing a novel soundtrack from an existing musical piece while preserving its structure and continuity from a music theoretical point of view. Existing approaches analyze a musical piece for possible cut points that allow the resynthesis of a novel soundtrack by lining up the source segments according to specified rules but fail to maintain musically correct song progression. Introducing the alignment of rhythmic and harmonic structures during transition point detection, we employ beat tracking as the analysis core component and take the human sound perception into account. Automatic segment rearrangement is improved by employing a novel belief propagation approach that enables user-defined constraints for the output soundtrack, allowing video editors or dance choreographers to tailor a soundtrack to their specific demands.
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.
Dynamic Time Warping Based 3D Contours
(The Eurographics Association, 2013) Croci, Simone; Smolic, Aljoscha; Wang, Oliver; Michael Bronstein and Jean Favre and Kai Hormann
In this work, we present a method for computing 3D contours from the silhouettes of objects in multiple views. Our approach unwraps contours into 1D signals and computes an efficient, globally optimal alignment using a modified dynamic time warping technique. Using our method, we can approximate real model geometry by interpolating the 3D contour on the billboard plane, thereby reducing the stereo problem to 1D and allowing for much more efficient and robust computation methods.
Integrated Multi-aspect Visualization of 3D Fluid Flows
(The Eurographics Association, 2013) Brambilla, Andrea; Andreassen, Øyvind; Hauser, Helwig; Michael Bronstein and Jean Favre and Kai Hormann
The motion of a fluid is affected by several intertwined flow aspects. Analyzing one aspect at a time can only yield partial information about the flow behavior. More details can be revealed by studying their interactions. Our approach enables the investigation of these interactions by simultaneously visualizing meaningful flow aspects, such as swirling motion and shear strain. We adopt the notions of relevance and coherency. Relevance identifies locations where a certain flow aspect is deemed particularly important. The related piece of information is visualized by a specific visual entity, placed at the corresponding location. Coherency instead represents the homogeneity of a flow property in a local neighborhood. It is exploited in order to avoid visual redundancy and to reduce occlusion and cluttering. We have applied our approach to three CFD datasets, obtaining meaningful insights.
Interactive Comparative Visualization of Multimodal Brain Tumor Segmentation Data
(The Eurographics Association, 2013) Lindemann, Florian; Laukamp, Kai; Jacobs, Andreas H.; Hinrichs, Klaus; Michael Bronstein and Jean Favre and Kai Hormann
We present a visualization system for the analysis of multi-modal segmentation data of brain tumors. Our system is designed to allow researchers and doctors a further investigation of segmented tumor data beyond a quantitative assessment of size. This includes the efficient visual analysis of the shape and relative position of the different, often overlapping segmented data modalities, using high quality 3D renderings of the data. Furthermore, our system provides visualization methods to compare tumor segmentation volumes acquired at various points of time, which helps the user to explore changes in shape and size before and after treatment. We also employ two novel interactive diagrams which allow the user to quickly navigate and analyze overlapping tumor regions. All methods are assembled and linked in a multi-view framework.
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.
Star Convex Cuts with Encoding Swaps for Fast Whole-Spine Vertebrae Segmentation in MRI
(The Eurographics Association, 2017) Rak, Marko; Tönnies, Klaus D.; Matthias Hullin and Reinhard Klein and Thomas Schultz and Angela Yao
We propose an automatic approach for fast vertebral body segmentation in three-dimensional magnetic resonance images of the whole spine. Previous works are limited to the lower thoracolumbar section and often take minutes to compute, which can be problematic in clinical routine or for data sets with numerous subjects. We address these limitations by a graph cut formulation. Our formulation involves appearance and shape information as well as star-convexity constraints to ensure a topologically correct segmentation for each vertebra. For close targets such as adjacent vertebrae, implementing star-convexity without fusing targets (naive binary formulations) or increasing run time/loosing optimality guarantees (multi-label formulations) is challenging. We provide a solution based on encoding swaps, which preserve optimality and ensure topological correctness between vertebrae. We validated our approach on two data sets. The first contains T1- and T2-weighted whole-spine images of 64 subjects. The second comprises 23 T2-weighted thoracolumbar images and is publicly available. Our results are competitive to previous works (or better) at a fraction of the run time. We yielded Dice coefficients of 85:1 +/- 4:4% and 89:7 +/- 2:3% with run times of 1:65 +/- 0:28 s and 2:73 +/- 0:36 s per vertebra on consumer hardware.
Visualizing Solar Dynamics Data
(The Eurographics Association, 2012) Machado, Gustavo M.; Sadlo, Filip; Müller, Thomas; Müller, Daniel; Ertl, Thomas; Michael Goesele and Thorsten Grosch and Holger Theisel and Klaus Toennies and Bernhard Preim
Solar dynamics data, particularly those from the Solar Dynamics Observatory, are now available in a sheer volume that is hard to investigate with traditional visualization tools, which mainly display 2D images. While the challenge of data access and browsing has been solved by web-based interfaces and efforts like the Helioviewer project, the approaches so far only provide 2D visualizations. We introduce the visualization of such data in the full 3D context, providing appropriate coordinate systems and projection techniques. We also apply and extend methods from volume rendering and flow visualization to 3D magnetic fields, which we derive from the sensor data in an interactive process, and introduce space-time visualization of photospheric data. Here, we concentrate on two solar phenomena: the structure and dynamics of coronal loops, and the development of the plasma convection in close vicinity of sunspots over time. Our approach avoids the time-coherence issue inherent in traditional magnetic field line placement, providing insight in the magnetic field and the structure of the coronal plasma. We are convinced that the presented techniques are applicable in many other fields such as the terrestrial magnetospheric physics, or magnetohydrodynamics simulations.

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