Martin Hering-Bertram

Extracting and Visualizing Structural Features in Environmental Point Cloud LiDaR Data Sets

We present a user-assisted approach to extracting and visualizing structural features from point clouds obtained by terrestrial and airborne laser scanning devices. We apply a multi-scale approach to express the membership of local point environments to corresponding geometric shape classes in terms of probability. This information is filtered and combined to establish feature graphs which can be visualized in combination with the color-encoded feature and structural probability estimates of the measured raw point data. Our method can be used, for example, for exploring geological point data scanned from multiple viewpoints.

Volume deformations in grid-less flow simulations

This paper presents a novel method for the extraction and visualization of volume deformations in grid‐less point based flow simulations. Our primary goals are the segmentation of different paths through a mixing device and the visualization of ellipsoidal particle deformations. The main challenges are the numerically efficient processing of deformation tensors and the robust integration of stream‐ and streaklines at boundaries of the dataset such that closed segments are obtained. Our results show two‐ and three‐dimensional particle deformations as well as the segmentation of volumes in stationary fields and areas in time‐dependent datasets taking consistent paths through a mixing device.

Listener-based Analysis of Surface Importance for Acoustic Metrics

Acoustic quality in room acoustics is measured by well defined quantities, like definition, which can be derived from simulated impulse response filters or measured values. These take into account the intensity and phase shift of multiple reflections due to a wave front emanating from a sound source. Definition (D50) and clarity (C50) for example correspond to the fraction of the energy received in total to the energy received in the first 50 ms at a certain listener position. Unfortunately, the impulse response measured at a single point does not provide any information about the direction of reflections, and about the reflection surfaces which contribute to this measure. For the visualization of room acoustics, however, this information is very useful since it allows to discover regions with high contribution and provides insight into the influence of all reflecting surfaces to the quality measure. We use the phonon tracing method to calculate the contribution of the reflection surfaces to the impulse response for different listener positions. This data is used to compute importance values for the geometry taking a certain acoustic metric into account. To get a visual insight into the directional aspect, we map the importance to the reflecting surfaces of the geometry. This visualization indicates which parts of the surfaces need to be changed to enhance the chosen acoustic quality measure. We apply our method to the acoustic improvement of a lecture hall by means of enhancing the overall speech comprehensibility (clarity) and evaluate the results using glyphs to visualize the clarity (C50) values at listener positions throughout the room.

High-Quality Rendering of Quartic Spline Surfaces on the GPU

We present a novel GPU-based algorithm for high-quality rendering of bivariate spline surfaces. An essential difference to the known methods for rendering graph surfaces is that we use quartic smooth splines on triangulations rather than triangular meshes. Our rendering approach is direct since we do not use an intermediate tessellation but rather compute ray-surface intersections (by solving quartic equations numerically) as well as surface normals (by using Bernstein-Bezier techniques) for Phong illumination on the GPU. Inaccurate shading and artifacts appearing for triangular tesselated surfaces are completely avoided. Level of detail is automatic since all computations are done on a per fragment basis. We compare three different (quasi-) interpolating schemes for uniformly sampled gridded data, which differ in the smoothness and the approximation properties of the splines. The results show that our hardware-based renderer leads to visualizations (including texturing, multiple light sources, environment mapping, and so forth) of highest quality.

Stream Volume Segmentation of Grid-Less Flow Simulation

We present a novel algorithm for the geometric extraction of stream volume segmentation for visualization of grid-less flow simulations. Our goal is the segmentation of different paths through a mixing tube where the flow is represented by scattered point sets approximated with moving least squares. The key challenges are thewatertight construction of boundary representations from separatrices. These are obtained by integrating and intersectingstream surfaces starting at separation and attachment lines at boundaries of flow obstacles. A major challenge is the robust integration of stream lines at boundaries with no-slip condition such that closed volume segments are obtained. Our results show the segmentation of volumes taking consistent paths through a mixing tube with six partitioning blades. Slicing these volumes provides valuable insight into the quality of the mixing process.

Sound tracing: rendering listener specific acoustic room properties

We present an acoustic rendering approach visualizing the listener‐specific contribution of frequency‐dependent pressure fields on a scene geometry with acoustic reflection and scattering properties. Our method facilitates the evaluation of simulated acoustics showing the effect of simulation parameters like absorption and scattering. The image‐based spatial localization of acoustic properties is complementary to the auditive evaluation by means of auralization. Our core contribution is a pressure‐based acoustic rendering equation and a corresponding raytracing method applying techniques from photorealistic rendering to the field of simulated room acoustics. Applications are directed at the visualization of interference patterns and analyzing the impact of acoustic reflection parameters.

On Mesh-Free Valley Surface Extraction with Application to Low Frequency Sound Simulation

Crease surfaces describe extremal structures of 3D scalar fields. We present a new region-growing-based approach to the meshless extraction of adaptive nonmanifold valley and ridge surfaces that overcomes limitations of previous approaches by decoupling point seeding and triangulation of the surface. Our method is capable of extracting valley surface skeletons as connected minimum structures. As our algorithm is inherently mesh-free and curvature adaptive, it is suitable for surface construction in fields with an arbitrary neighborhood structure. As an application for insightful visualization with valley surfaces, we choose a low frequency acoustics simulation. We use our valley surface construction approach to visualize the resulting complex-valued scalar pressure field for arbitrary frequencies to identify regions of sound cancellation. This provides an expressive visualization of the topology of wave node and antinode structures in simulated acoustics.

Adaptive quasi-interpolating quartic splines

We present an adaptive quasi-interpolating quartic spline construction for regularly sampled surface data. The method is based on a uniform quasi-interpolating scheme, employing quartic triangular patches with C1-continuity and optimal approximation order within this class. Our contribution is the adaption of this scheme to surfaces of varying geometric complexity, where the tiling resolution can be locally defined, for example driven by approximation errors. This way, the construction of high-quality spline surfaces is enhanced by the flexibility of adaptive pseudo-regular triangle meshes. Numerical examples illustrate the use of this method for adaptive terrain modeling, where uniform schemes produce huge numbers of patches.

Topological flow volume extraction from time-surface maps

Abstract The input–output behavior or flow transfer function of typical mixing processes is highly relevant to the analysis of the dynamic system and its mixing quality. We aim to visualize this behavior by extracting topologically relevant flow volumes from statistics accumulated during particle traversal of the flow field. To guarantee a sufficiently dense sampling of the flow field, we use adaptive time-surfaces for the computation of these trajectory statistics. The proposed volume extraction technique operates in parameter space of the computed time-surfaces and facilitates fast extraction of boundary geometry at different levels of detail. Our results visualize flow transfer functions in the form of volumes for extrema of different time-surface statistics and demonstrate their benefit for flow analysis.

Interactive Visualization of Scattered Moment Tensor Data

Moment tensors derived from seismic measurements during earthquakes are related to stress tensors and keep important information about surface displacement in the earths mantle. We present methods facilitating an interactive visualization of scattered moment data to support earthquake and displacement analysis. For this goal, we combine and link visualizations of spatial location and orientation information derived from moment tensor decompositions. Furthermore, we contribute new tensor glyphs highlighting the indefinite character of moment tensors as well as novel tensor clustering and averaging techniques to aid interactive visual analysis and ease the challenges of interpreting moment tensor data.