Particle-Based Fused Rendering

In this chapter, we propose a fused rendering technique that can integrally handle multiple irregular volumes. Although there is a strong requirement for understanding large-scale datasets generated from coupled simulation techniques such as computational structure mechanics (CSM) and computational fluid dynamics (CFD), there is no fused rendering technique to the best of our knowledge. For this purpose, we can employ the particle-based volume rendering (PBVR) technique for each irregular volume dataset. Since the current PBVR technique regards an irregular cell as a planar footprint during depth evaluation, the straightforward employment causes some artifacts especially at the cell boundaries. To solve the problem, we calculate the depth value based on the assumption that the opacity describes the cumulative distribution function (CDF) of a probability variable, w, which shows a length from the entry point in the fragment interval in the cell. In our experiments, we applied our method to numerical simulation results in which two different irregular grid cells are defined in the same space and confirmed its effectiveness with respect to the image quality

Layout of Multiple Views for Volume Visualization: A User Study

Abstract. Volume visualizations can have drastically different appearances when viewed using a variety of transfer functions. A problem then occurs in trying to organize many different views on one screen. We conducted a user study of four layout techniques for these multiple views. We timed participants as they separated different aspects of volume data for both time-invariant and time-variant data using one of four different layout schemes. The layout technique had no impact on performance when used with time-invariant data. With time-variant data, however, the multiple view layouts all resulted in better times than did a single view interface. Surprisingly, different layout techniques for multiple views resulted in no noticeable difference in user performance. In this paper, we describe our study and present the results, which could be used in the design of future volume visualization software to improve the productivity of the scientists who use it

Transition Contour Synthesis with Dynamic Patch Transitions

In this article, we present a novel approach for modulating the shape of transitions between terrain materials to produce detailed and varied contours where blend resolution is limited. Whereas texture splatting and blend mapping add detail to transitions at the texel level, our approach addresses the broader shape of the transition by introducing intermittency and irregularity. Our results have proven that enriched detail of the blend contour can be achieved with a performance competitive to existing approaches without additional texture, geometry resources, or asset preprocessing. We achieve this by compositing blend masks on-the-fly with the subdivision of texture space into differently sized patches to produce irregular contours from minimal artistic input. Our approach is of particular importance for applications where GPU resources or artistic input is limited or impractical

Multiscale correlative tomography: an investigation of creep cavitation in 316 stainless steel

Creep cavitation in an ex-service nuclear steam header Type 316 stainless steel sample is investigated through a multiscale tomography workflow spanning eight orders of magnitude, combining X-ray computed tomography (CT), plasma focused ion beam (FIB) scanning electron microscope (SEM) imaging and scanning transmission electron microscope (STEM) tomography. Guided by microscale X-ray CT, nanoscale X-ray CT is used to investigate the size and morphology of cavities at a triple point of grain boundaries. In order to understand the factors affecting the extent of cavitation, the orientation and crystallographic misorientation of each boundary is characterised using electron backscatter diffraction (EBSD). Additionally, in order to better understand boundary phase growth, the chemistry of a single boundary and its associated secondary phase precipitates is probed through STEM energy dispersive X-ray (EDX) tomography. The difference in cavitation of the three grain boundaries investigated suggests that the orientation of grain boundaries with respect to the direction of principal stress is important in the promotion of cavity formation

Volumetric real-time particle-based representation of large unstructured tetrahedral polygon meshes

In this paper we propose a particle-based volume rendering approach for unstructured, three-dimensional, tetrahedral polygon meshes. We stochastically generate millions of particles per second and project them on the screen in real-time. In contrast to previous rendering techniques of tetrahedral volume meshes, our method does not need a prior depth sorting of geometry. Instead, the rendered image is generated by choosing particles closest to the camera. Furthermore, we use spatial superimposing. Each pixel is constructed from multiple subpixels. This approach not only increases projection accuracy, but allows also a combination of subpixels into one superpixel that creates the well-known translucency effect of volume rendering. We show that our method is fast enough for the visualization of unstructured three-dimensional grids with hard real-time constraints and that it scales well for a high number of particles

VIOLA - A multi-purpose and web-based visualization tool for neuronal-network simulation output

Neuronal network models and corresponding computer simulations are invaluable tools to aid the interpretation of the relationship between neuron properties, connectivity and measured activity in cortical tissue. Spatiotemporal patterns of activity propagating across the cortical surface as observed experimentally can for example be described by neuronal network models with layered geometry and distance-dependent connectivity. The interpretation of the resulting stream of multi-modal and multi-dimensional simulation data calls for integrating interactive visualization steps into existing simulation-analysis workflows. Here, we present a set of interactive visualization concepts called views for the visual analysis of activity data in topological network models, and a corresponding reference implementation VIOLA (VIsualization Of Layer Activity). The software is a lightweight, open-source, web-based and platform-independent application combining and adapting modern interactive visualization paradigms, such as coordinated multiple views, for massively parallel neurophysiological data. For a use-case demonstration we consider spiking activity data of a two-population, layered point-neuron network model subject to a spatially confined excitation originating from an external population. With the multiple coordinated views, an explorative and qualitative assessment of the spatiotemporal features of neuronal activity can be performed upfront of a detailed quantitative data analysis of specific aspects of the data. Furthermore, ongoing efforts including the European Human Brain Project aim at providing online user portals for integrated model development, simulation, analysis and provenance tracking, wherein interactive visual analysis tools are one component. Browser-compatible, web-technology based solutions are therefore required. Within this scope, with VIOLA we provide a first prototype.Comment: 38 pages, 10 figures, 3 table

Flux-Limited Diffusion for Multiple Scattering in Participating Media

For the rendering of multiple scattering effects in participating media, methods based on the diffusion approximation are an extremely efficient alternative to Monte Carlo path tracing. However, in sufficiently transparent regions, classical diffusion approximation suffers from non-physical radiative fluxes which leads to a poor match to correct light transport. In particular, this prevents the application of classical diffusion approximation to heterogeneous media, where opaque material is embedded within transparent regions. To address this limitation, we introduce flux-limited diffusion, a technique from the astrophysics domain. This method provides a better approximation to light transport than classical diffusion approximation, particularly when applied to heterogeneous media, and hence broadens the applicability of diffusion-based techniques. We provide an algorithm for flux-limited diffusion, which is validated using the transport theory for a point light source in an infinite homogeneous medium. We further demonstrate that our implementation of flux-limited diffusion produces more accurate renderings of multiple scattering in various heterogeneous datasets than classical diffusion approximation, by comparing both methods to ground truth renderings obtained via volumetric path tracing.Comment: Accepted in Computer Graphics Foru

Paleokarst reservoir modelling - A concept-driven approach

A significant proportion of the world's hydrocarbon production comes from paleokarst reservoirs. Although these reservoirs boast some of the most productive wells in oil history, the recovery factor is relatively low (RFmean: 32%) compared to other carbonate reservoirs (RFmean: 37 - 51%). The low recovery could relate to current reservoir modelling approaches potentially yielding inaccurate resource estimates or early water-breakthrough. Conventional industry-standard reservoir modelling software suites do not have dedicated workflows or add-ins for handling the complex morphologies commonly associated with paleokarst. Current modelling approaches are often datadriven (conditioned on available seismic and well data) and employ adapted or modified versions of stochastic reservoir modelling workflows used for siliciclastic and carbonate reservoirs. However, many paleokarst features are below seismic resolution, and the representativity of individual well data is often challenging to assess. Consequently, data-driven models often fail to render the connectivity, geometry, and volume of karst features. Karst is the predecessor to paleokarst, and therefore a genetic approach employing existent information from recent karst systems may be a good starting point for generating analogues to paleokarst reservoirs. A concept-driven approach, in combination with current data-driven modelling approaches, may enable model rendering that more closely echoes actual paleokarst reservoir architectures. However, only a few conceptual modelling methods are publicly available and described in the literature. The drawbacks with the available methods are that they under-/overestimate the cave volumes, fail to provide realistic cave morphologies, and forecast clastic sediment infill, and do not differentiate between preserved and collapsed caverns. Consequently, post-collapse reservoir morphologies, volumes and facies distributions may be rendered inaccurately. This thesis aims to address the shortcomings of currently available conceptual methods and present a novel concept-driven workflow for paleokarst reservoir modelling. A novel methodology for geocellular rendering of karst systems is presented in this thesis. The method utilizes modern cave-survey data to generate dense, equally spaced point-clouds (infilling the cave periphery). These point clouds can be used to discretize the karst systems in a geocellular framework by geometrical modelling. The volumetric and geometric rendering of the method is compared with two pre-established methods and benchmarked against the cave survey. The results show that the new method offers improved volumetric and geometric geocellular rendering compared to the preestablished methods and are comparable to that of the cave survey. A pilot study using a well-known and pre-established geophysical method, electrical resistivity tomography (ERT), was carried out in the Maaras cave system in northern Greece to evaluate the large-scale volumetric significance and spatial distribution of clastic sediments infilling karst cavities. ERT proved to be a practical and useful method for differentiating mesoscale (>2.5 m2) stratigraphic heterogeneity. Resistivity contrasts allowed the identification of sedimentary thickness variations, interbedded breccias, and cave floor. Results showed that the siliciclastic sediment thickness varied from 25 m to >45 m, occupying a minimum of 69-95 % of the available accommodation space. Finally, a novel interactive tool for evaluating cavern stability and forward model collapse and infill processes was developed. The tool employs conventional cave survey data, field measurements and geomechanical data of the host rock to simulate potential post-collapse morphologies and generate spatial output data suitable for geocellular modelling. Collapse propagation, and eventually the volume affected by the collapse, is controlled by user-defined paleokarst facies proportions and associated average porosities following a “mass-balance-principle” (i.e., porosity is final and only redistributed over a larger volume). Three different collapse scenarios were modelled using the Agios Georgios cave system in northern Greece as an analogue. The results show that it is feasible to use cave surveys to simulate collapse and infill processes and estimate the final paleokarst reservoir architecture. The morphology, volume and relative facies-proportions rendered in the reservoir models are comparable to those calculated in the forward collapse modelling tool, indicating that the geocellular model echoes the simulation. The results also show that the vertical continuity and target volume of a reservoir increases significantly with increasing bedding dip. This suggests that improved forecasting of the final reservoir architecture may optimise well positioning, production planning and eventually improve recovery prediction.Doktorgradsavhandlin