New techniques for the scientific visualization of three-dimensional multi-variate and vector fields

Volume rendering allows us to represent a density cloud with ideal properties (single scattering, no self-shadowing, etc.). Scientific visualization utilizes this technique by mapping an abstract variable or property in a computer simulation to a synthetic density cloud. This thesis extends volume rendering from its limitation of isotropic density clouds to anisotropic and/or noisy density clouds. Design aspects of these techniques are discussed that aid in the comprehension of scientific information. Anisotropic volume rendering is used to represent vector based quantities in scientific visualization. Velocity and vorticity in a fluid flow, electric and magnetic waves in an electromagnetic simulation, and blood flow within the body are examples of vector based information within a computer simulation or gathered from instrumentation. Understand these fields can be crucial to understanding the overall physics or physiology. Three techniques for representing three-dimensional vector fields are presented: Line Bundles, Textured Splats and Hair Splats. These techniques are aimed at providing a high-level (qualitative) overview of the flows, offering the user a substantial amount of information with a single image or animation. Non-homogenous volume rendering is used to represent multiple variables. Computer simulations can typically have over thirty variables, which describe properties whose understanding are useful to the scientist. Trying to understand each of these separately can be time consuming. Trying to understand any cause and effect relationships between different variables can be impossible. NoiseSplats is introduced to represent two or more properties in a single volume rendering of the data. This technique is also aimed at providing a qualitative overview of the flows

Visual Simulation of Flow

We have adopted a numerical method from computational fluid dynamics, the Lattice Boltzmann Method (LBM), for real-time simulation and visualization of flow and amorphous phenomena, such as clouds, smoke, fire, haze, dust, radioactive plumes, and air-borne biological or chemical agents. Unlike other approaches, LBM discretizes the micro-physics of local interactions and can handle very complex boundary conditions, such as deep urban canyons, curved walls, indoors, and dynamic boundaries of moving objects. Due to its discrete nature, LBM lends itself to multi-resolution approaches, and its computational pattern, which is similar to cellular automata, is easily parallelizable. We have accelerated LBM on commodity graphics processing units (GPUs), achieving real-time or even accelerated real-time on a single GPU or on a GPU cluster. We have implemented a 3D urban navigation system and applied it in New York City with real-time live sensor data. In addition to a pivotal application in simulation of airborne contaminants in urban environments, this approach will enable the development of other superior prediction simulation capabilities, computer graphics and games, and a novel technology for computational science and engineering

New techniques for the scientific visualization of three-dimensional multi-variate and vector fields

Volume rendering allows us to represent a density cloud with ideal properties (single scattering, no self-shadowing, etc.). Scientific visualization utilizes this technique by mapping an abstract variable or property in a computer simulation to a synthetic density cloud. This thesis extends volume rendering from its limitation of isotropic density clouds to anisotropic and/or noisy density clouds. Design aspects of these techniques are discussed that aid in the comprehension of scientific information. Anisotropic volume rendering is used to represent vector based quantities in scientific visualization. Velocity and vorticity in a fluid flow, electric and magnetic waves in an electromagnetic simulation, and blood flow within the body are examples of vector based information within a computer simulation or gathered from instrumentation. Understand these fields can be crucial to understanding the overall physics or physiology. Three techniques for representing three-dimensional vector fields are presented: Line Bundles, Textured Splats and Hair Splats. These techniques are aimed at providing a high-level (qualitative) overview of the flows, offering the user a substantial amount of information with a single image or animation. Non-homogenous volume rendering is used to represent multiple variables. Computer simulations can typically have over thirty variables, which describe properties whose understanding are useful to the scientist. Trying to understand each of these separately can be time consuming. Trying to understand any cause and effect relationships between different variables can be impossible. NoiseSplats is introduced to represent two or more properties in a single volume rendering of the data. This technique is also aimed at providing a qualitative overview of the flows

Clouding tracing: Visualization of the mixing of fluid elements in convection-diffusion systems

This paper describes a highly interactive method for computer visualization of the basic physical process of dispersion and mixing of fluid elements in convection-diffusion systems. It is based on transforming the vector field from a traditionally Eulerian reference frame into a Lagrangian reference frame. Fluid elements are traced through the vector field for the mean path as well as the statistical dispersion of the fluid elements about the mean position by using added scalar information about the root mean square value of the vector field and its Lagrangian time scale. In this way, clouds of fluid elements are traced and are not just mean paths. We have used this method to visualize the simulation of an industrial incinerator to help identify mechanisms for poor mixing

The State of the Art in Flow Visualization: Dense and Texture-Based Techniques

Flow visualization has been a very attractive component of scientific visualization research for a long time. Usually very large multivariate datasets require processing. These datasets often consist of a large number of sample locations and several time steps. The steadily increasing performance of computers has recently become a driving factor for a reemergence in flow visualization research, especially in texture-based techniques. In this paper, dense, texture-based flow visualization techniques are discussed. This class of techniques attempts to provide a complete, dense representation of the flow field with high spatio-temporal coherency. An attempt of categorizing closely related solutions is incorporated and presented. Fundamentals are shortly addressed as well as advantages and disadvantages of the methods. Categories and Subject Descriptors (according to ACM CCS): I.3 [Computer Graphics]: visualization, flow visualization, computational flow visualizatio

ICASE/LaRC Symposium on Visualizing Time-Varying Data

Time-varying datasets present difficult problems for both analysis and visualization. For example, the data may be terabytes in size, distributed across mass storage systems at several sites, with time scales ranging from femtoseconds to eons. In response to these challenges, ICASE and NASA Langley Research Center, in cooperation with ACM SIGGRAPH, organized the first symposium on visualizing time-varying data. The purpose was to bring the producers of time-varying data together with visualization specialists to assess open issues in the field, present new solutions, and encourage collaborative problem-solving. These proceedings contain the peer-reviewed papers which were presented at the symposium. They cover a broad range of topics, from methods for modeling and compressing data to systems for visualizing CFD simulations and World Wide Web traffic. Because the subject matter is inherently dynamic, a paper proceedings cannot adequately convey all aspects of the work. The accompanying video proceedings provide additional context for several of the papers

Perception of Multisensory Wind Representation in Virtual Reality

International audienceThe set of physical and sensitive phenomena that interacts with the urban morphology acts on the resulting perception from the users of a place. Its study and representation provides elements beyond the aesthetics aspects that can allow a better understanding of the space and future urban projects. We aim to analyze the effects of three different wind representations in terms of perception and sense of presence in virtual reality (VR). We focus on the following conditions: (R) reference scene with the audiovisual representation of the mechanical effects of the wind on the elements of the context, (V) reference scene plus the visualization of the wind flow, present (among others) in the architecture field, (T) reference scene plus tactile restitution of wind and eventually (V+T) assembling all previous conditions. For the experiment, we present to the participants (R), then (V) followed by (T), and finish with (V+T). 37 participants evaluated 12 different stop points (divided into four routes in the same simulated street), where they had to determine the perceived wind force and direction concerning the four different conditions (each one corresponding to one route). At the end of each route, participants evaluated their sense of presence in the VR scene. Our analysis showed significant effects of tactile restitution over the visual effects used in the study, both for understanding wind properties and for increasing the sense of presence in the VR scene. In terms of wind direction, (T) reduced the estimation error by 27% compared to (V). Concerning wind force, the reduction was 9.8%. As far as presence was concerned, (T) increased the sense of presence by 12.2% compared to (V)

Efficient algorithms for the realistic simulation of fluids

Nowadays there is great demand for realistic simulations in the computer graphics field. Physically-based animations are commonly used, and one of the more complex problems in this field is fluid simulation, more so if real-time applications are the goal. Videogames, in particular, resort to different techniques that, in order to represent fluids, just simulate the consequence and not the cause, using procedural or parametric methods and often discriminating the physical solution. This need motivates the present thesis, the interactive simulation of free-surface flows, usually liquids, which are the feature of interest in most common applications. Due to the complexity of fluid simulation, in order to achieve real-time framerates, we have resorted to use the high parallelism provided by actual consumer-level GPUs. The simulation algorithm, the Lattice Boltzmann Method, has been chosen accordingly due to its efficiency and the direct mapping to the hardware architecture because of its local operations. We have created two free-surface simulations in the GPU: one fully in 3D and another restricted only to the upper surface of a big bulk of fluid, limiting the simulation domain to 2D. We have extended the latter to track dry regions and is also coupled with obstacles in a geometry-independent fashion. As it is restricted to 2D, the simulation loses some features due to the impossibility of simulating vertical separation of the fluid. To account for this we have coupled the surface simulation to a generic particle system with breaking wave conditions; the simulations are totally independent and only the coupling binds the LBM with the chosen particle system. Furthermore, the visualization of both systems is also done in a realistic way within the interactive framerates; raycasting techniques are used to provide the expected light-related effects as refractions, reflections and caustics. Other techniques that improve the overall detail are also applied as low-level detail ripples and surface foam