VG: Eurographics/IEEE VGTC Symposium on Volume Graphics

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3D Reconstruction of Emission and Absorption in Planetary Nebulae
(The Eurographics Association, 2007) Lintu, Andrei; Lensch, Hendrik P. A.; Magnor, Marcus; El-Abed, Sascha; Seidel, Hans-Peter; H.-C. Hege and R. Machiraju and T. Moeller and M. Sramek
This paper addresses the problem of reconstructing the 3D structure of planetary nebulae from 2D observations. Assuming axial symmetry, our method jointly reconstructs the distribution of dust and ionized gas in the nebulae from observations at two different wavelengths. In an inverse rendering framework we optimize for the emission and absorption densities which are correlated to the gas and dust distribution present in the nebulae. First, the density distribution of the dust component is estimated based on an infrared image, which traces only the dust distribution due to its intrinsic temperature. In a second step, we optimize for the gas distribution by comparing the rendering of the nebula to the visible wavelength image. During this step, besides the emission of the ionized gas, we further include the effect of absorption and scattering due to the already estimated dust distribution. Using the same approach, we can as well start with a radio image from which the gas distribution is derived without absorption, then deriving the dust distribution from the visible wavelength image considering absorption and scattering. The intermediate steps and the final reconstruction results are visualized at real-time frame rates using a volume renderer. Using our method we recover both gas and dust density distributions present in the nebula by exploiting the distinct absorption or emission parameters at different wavelengths.
Accelerated Light Propagation Through Participating Media
(The Eurographics Association, 2007) Lee, Richard; O'Sullivan, Carol; H.-C. Hege and R. Machiraju and T. Moeller and M. Sramek
Monte Carlo path tracing is a simple and effective way to solve the volume rendering equation. However, propagating light paths through participating media can be very costly because of the need to simulate potentially many scattering events. This paper presents a simple technique to accelerate path tracing of homogeneous participating media. We use a traditional path tracer for scattering near the surface but switch to a new approach for handling paths that penetrate far enough inside the medium. These paths are determined by sampling from a set of precomputed probability distributions, which avoids the need to simulate individual scattering events or perform ray intersection tests with the environment. We demonstrate cases where our approach leads to accurate and more efficient rendering of participating media, including subsurface scattering in translucent materials.
Accelerated, High-Quality Refraction Computations for Volume Graphics
(The Eurographics Association, 2005) Li, Shengying; Mueller, Klaus; Klaus Mueller and Thomas Ertl and Eduard Groeller
We present an efficient framework for the high-quality rendering of discretely sampled surface-based objects with refractive effects. This requires an accurate estimation of the refraction coefficients, paired with efficient and accurate surface detection, space traversal, and backdrop image sampling. Our framework achieves these goals, by employing a high-quality spline-based filter in conjunction with a novel filtered octree space decomposition with pre-classified cells that is carefully matched to the filter and voxel neighborhood characteristics. Here, we benefit greatly from the non-negativity of the B-Spline kernel. Finally, we describe an innovative scheme that achieves the high quality of pixel super-sampling on a flat backdrop plane without the overhead of tracing the actual rays across the refractive object.
Accelerating Volume Raycasting using Occlusion Frustums
(The Eurographics Association, 2008) Mensmann, Jörg; Ropinski, Timo; Hinrichs, Klaus; Hans-Christian Hege and David Laidlaw and Renato Pajarola and Oliver Staadt
GPU-based volume raycasting allows to produce high quality renderings on current graphics hardware. The use of such raycasters is on the rise due to their inherent flexibility as well as the advances in hardware performance and functionality. Although recent raycasting systems achieve interactive frame rates on high-end graphics hardware, further improved performance would enable more complex rendering techniques, e. g., advanced illumination models. In this paper we introduce a novel approach to empty space leaping in order to reduce the number of costly volume texture fetches during ray traversal. We generate an optimized proxy geometry for raycasting which is based on occlusion frustums obtained from previous frames. Our technique does not rely on any preprocessing, introduces no image artifacts, and in contrast to previous point-based methods works also for non-continuous view changes. Besides the technical realization and the performance results, we also discuss the potential problems of ray coherence in relation to our approach and restrictions in current GPU architectures. The presented technique has been implemented using fragment and geometry shaders and can be integrated easily into existing raycasting systems.
Accelerating Voxel-Based Terrain Rendering with Keyframe-Free Image-Based Rendering
(The Eurographics Association, 2001) Qin, Jiafa; MingWan,; Qu, Huamin; Kaufman, Arie; K. Mueller and A. Kaufman
We propose a voxel-based terrain rendering method which incorporates a novel keyframe-free image-based rendering algorithm and a new heuristic ray coherence raycasting algorithm. The current image is generated by warping the previous image with a revised 3D warping algorithm and filling holes by raycasting, accelerated by ray coherence and multiresolution ray traversal. This method not only achieves good performance, but also allows arbitrary viewing directions. We further accelerate the rendering with multiprocessor parallelism and have achieved a real-time rendering rate of 30Hz on a 16-processor SGI Power Challenge.
Accuracy-Based Sampling and Reconstruction with Adaptive Grid for Parallel Hierarchical Tetrahedrization
(The Eurographics Association, 2003) T.Tanaka, Hiromi; Takama, Yasufumi; Wakabayashi, Hiroki; I. Fujishiro and K. Mueller and A. Kaufman
Recent advances in volume scanning techniques have made the task of acquiring volume data of 3-D objects easier and more accurate. Since the quantity of such acquired data is generally very large, a volume model capable of compressing data while maintaining a specified accuracy is required. The objective of this work is to construct a multi resolution tetrahedra representation of input volume data. This representation adapts to local field properties while preserving their discontinuities. In this paper, we present an accuracy-based adaptive sampling and reconstruction technique, we call an adaptive grid, for hierarchical tetrahedrization of C1 continuous volume data. We have developed a parallel algorithm of adaptive grid generation that recursively bisects tetrahedra gird elements by increasing the number of grid nodes, according to local field properties and such as orientation and curvature of isosurfaces, until the entire volume has been approximated within a specified level of view-invariant accuracy. We have also developed a parallel algorithm that detects and preserves bothC0 andC1 discontinuities of field values, without the formation of cracks which normally occur during independent subdivision. Experimental results demonstrate the validity and effusiveness of the proposed approach.
Adaptive Sampling and Rendering of Fluids on the GPU
(The Eurographics Association, 2008) Zhang, Yanci; Solenthaler, Barbara; Pajarola, Renato; Hans-Christian Hege and David Laidlaw and Renato Pajarola and Oliver Staadt
In this paper, we propose a novel GPU-friendly algorithm for the Smoothed Particle Hydrodynamics (SPH) simulation for weakly compressible fluids. The major goal of our algorithm is to implement a GPU-based SPH simulation that can simulate and render a large number of particles at interactive speed. Additionally, our algorithm exhibits the following three features. Firstly, our algorithm supports adaptive sampling of the fluids. Particles can be split into several sub-particles in geometrically complex regions to provide a more accurate simulation. At the same time, nearby particles deep inside the fluids are merged to a single particle to reduce the number of particles. Secondly, the fluids are visualized by directly computing the intersection between ray and an isosurface defined by the surface particles. A dynamic particle grouping algorithm and equation solver are employed to quickly find the ray-isosurface intersection. Thirdly, based on the observation that the SPH simulation is a naturally parallel algorithm, the whole SPH simulation, including the adaptive sampling of the fluids as well as surface particle rendering, is executed on the GPU to fully utilize the computational power and parallelism of modern graphics hardware. Our experimental data shows that we can simulate about 50K adaptively sampled particles, or up to 120K particles in the fixed sampling case at a rate of approximately 20 time steps per second.
Adaptive Sampling in Single Pass, GPU-based Raycasting of Multiresolution Volumes
(The Eurographics Association, 2006) Ljung, Patric; Raghu Machiraju and Torsten Moeller
This paper presents a novel direct volume rendering technique for adaptive object- and image-space sampling density of multiresolution volumes. The raycasting is implemented entirely on the GPU in a single pass fragment program which adapts the sampling density along rays, guided by block resolutions. The multiresolution volumes are provided by a transfer function based level-of-detail scheme adaptively loading large out-of-core volumes. Adaptive image-space sampling is achieved by gathering projected basic volume block statistics for screen tiles and then allocating a level-of-detail for each tile. This combination of techniques provides a significant reduction of processing requirements while maintaining high quality rendering.
Advanced Light Material Interaction for Direct Volume Rendering
(The Eurographics Association, 2010) Lindemann, Florian; Ropinski, Timo; Ruediger Westermann and Gordon Kindlmann
In this paper we present a heuristic approach for simulating advanced light material interactions in the context of interactive volume rendering. In contrast to previous work, we are able to incorporate complex material functions, which allow to simulate reflectance and scattering. We exploit a common representation of these material properties based on spherical harmonic basis functions, to combine the achieved reflectance and scattering effects with natural lighting conditions, i. e., incorporating colored area light sources. To achieve these goals, we introduce a modified SH projection technique, which is not just tailored at a single material category, but adapts to the present material. Thus, reflecting and scattering materials as assigned trough the transfer function can be captured in a unified approach. We will describe the required extensions to the standard volume rendering integral and present an approximation which allows to realize the material effects in order to achieve interactive frame rates. By exploiting a combination of CPU and GPU processing, we are able to modify material properties and can change the illumination conditions interactively. We will demonstrate the outcome of the proposed approach based on renderings of real-world data sets and report the achieved computation times.
Applications of Optimal Sampling Lattices for Volume Acquisition via 3D Computed Tomography
(The Eurographics Association, 2007) Xu, Fang; Mueller, Klaus; H.-C. Hege and R. Machiraju and T. Moeller and M. Sramek
There has been mounting evidence that the familiar Cartesian lattices, while convenient for signal processing and representation, are sub-optimal when it comes to signal fidelity. More suitable in this respect are optimal sampling lattices, such as the Hexagonal and Body Centered Cartesian (BCC) lattice, and recent work has employed these in the areas of volume rendering and image processing. In this paper we explore various applications of these lattices within the context of 3D Computed Tomographic Reconstruction, both in terms of the (2D) detector and the (3D) reconstructed object, and a theoretical analysis is provided. We combine this analysis with a practical application, that is, the use of these lattices within a real-time GPU-accelerated 3D reconstruction platform, in which performance is also of an immediate concern.
An Architecture For Interactive Tetrahedral Volume Rendering
(The Eurographics Association, 2001) King, Davis; Wittenbrink, Craig M.; Wolters, Hans J.; K. Mueller and A. Kaufman
We present a new architecture for interactive unstructured volume rendering. Our system moves all the computations necessary for order-independent transparency and volume scan conversion from the CPU to the graphics hardware, and it makes a software sorting pass unnecessary. It therefore provides the same advantages for volume data that triangle-processing hardware provides for surfaces. To address a remaining bottleneck the bandwidth between main memory and the graphics processor we introduce two new primitives, tetrahedral strips and tetrahedral fans. These primitives allow performance improvements in rendering tetrahedral meshes similar to the improvements triangle strips and fans allow in rendering triangle meshes. We provide new techniques for generating tetrahedral strips that achieve, on the average, strip lengths of 17 on representative datasets. The combined effect of our architecture and new primitives is a 72 to 85 times increase in performance over triangle graphics hardware approaches. These improvements make it possible to use volumetric tetrahedral meshes in interactive applications.
Automatic Feature Modeling Techniques for Volume Segmentation Applications
(The Eurographics Association, 2007) Huang, Runzhen; Yu, Hongfeng; Ma, Kwan-Liu; Staadt, Oliver; H.-C. Hege and R. Machiraju and T. Moeller and M. Sramek
In many volume segmentation and visualization tasks, the ability to correctly identify the boundary surface of each volumetric feature of interest in the data is desirable. This surface can be used in subsequent quantitative studies of the segmented features. In this paper, we present an automatic approach to generate accurate representations of a feature of interest from volume segmentation. Our method first locates a set of points, which tightly define the boundary of the volumetric feature. This set of points can then be used to construct a boundary surface mesh. We also describe how to construct an anti-aliased volume representation of the segmented feature from this point set to enable high-quality volume rendering of the feature. These three representations - point set, boundary surface mesh, and anti-aliased volume segment - have a wide variety of applications.
Capture and Review of Interactive Volumetric Manipulations for Surgical Training
(The Eurographics Association, 2006) Kerwin, Thomas; Shen, Han-Wei; Stredney, Don; Raghu Machiraju and Torsten Moeller
In this paper, we present a system to capture efficiently a given user s interaction with a simulation system involving the procedural removal of material inside a volume, and to allow for a full 3D, lossless reviewing of that interaction at a later date. We describe an extension of this system to enable reviewing to occur at arbitrary points in the surgical procedure. The extension uses a combination of volume snapshots and event recording to be efficient in both time and space requirements.
Cell Projection of Convex Polyhedra
(The Eurographics Association, 2003) Roettger, Stefan; Ertl, Thomas; I. Fujishiro and K. Mueller and A. Kaufman
Finite element methods commonly use unstructured grids as the computational domain. As a matter of fact, the volume visualization of these unstructured grids is a time consuming task. Here, the fastest known object order algorithm is the projected tetrahedra algorithm of Shirley and Tuchman. Even with the upcoming of programmable graphics hardware, the rendering performance did not keep up with the growing complexity of the simulation data. In this paper we strive to improve the performance of the cell projection technique by posing several restrictions on the optical model. This allows us to devise a simple but fast hardware-accelerated algorithm which is able to project arbitrary polyhedral cells, that is tetrahedra, prisms, hexahedra, etc. For this reason, our algorithm is well suited for the display of unstructured FEM meshes with mixed cell types, but it is also applicable to the real-time display of gaseous phenonema, such as fire and ground fog.
Chronovolumes: A Direct Rendering Technique for Visualizing Time-Varying Data
(The Eurographics Association, 2003) Woodring, Jonathan; Shen, Han-Wei; I. Fujishiro and K. Mueller and A. Kaufman
We present a new method for displaying time varying volumetric data. The core of the algorithm is an integration through time producing a single view volume that captures the essence of multiple time steps in a sequence. The resulting view volume then can be viewed with traditional raycasting techniques. With different time integration functions, we can generate several kinds of resulting chronovolumes, which illustrate differing types of time varying features to the user. By utilizing graphics hardware and texture memory, the integration through time can be sped up, allowing the user interactive control over the temporal transfer function and exploration of the data.
Combining Point Clouds and Volume Objects in Volume Scene Graphs
(The Eurographics Association, 2005) Chen, Min; Klaus Mueller and Thomas Ertl and Eduard Groeller
This paper describes an extension to the technical framework of Constructive Volume Geometry (CVG) in order to accommodate point clouds in volume scene graphs. It introduces the notion of point-based volume object (PBVO) that is characterized by the opacity, rather than the geometry, of a point cloud. It examines and compares several radial basis functions (RBFs), including the one proposed in this paper, for constructing scalar fields from point clouds. It applies basic CVG operators to PBVOs and demonstrates the inter-operability of PBVOs with conventional volume objects including those procedurally defined and those constructed from volume datasets. It presents an octree-based algorithm for reducing the complexity in rendering a PBVO with a large number of points, and a set of testing results showing a significant speedup when an octree is deployed for rendering PBVOs.
Complementary Shape Comparison with Additional Properties
(The Eurographics Association, 2006) Zhang, Xiaoyu; Raghu Machiraju and Torsten Moeller
We present an algorithm for comparing 3D shapes by considering their pockets in the complementary space. The pockets of a closed compact surface can be represented by a 3D volumetric function. Multi-resolution dual contour trees are constructed from the pocket functions to efficiently match them in an affine-invariant way. DCTs are simplified data structures computed from contour trees (CT) of 3D functions. The DCTs capture the important features of the volumetric functions and are not sensitive to noises. Each node of a DCT corresponds to an interval volume and is tagged with geometrical, topological, and functional attributes. Similarities among shapes are compared by matching nodes from multi-resolution DCTs and calculating the score based on the attributes of the matched nodes. This method is particularly useful for comparing complicated molecular shapes, for which other properties such as electrostatic potentials can be added as additional attributes to improve performance.
Concurrent Volume Visualization of Real-Time fMRI
(The Eurographics Association, 2010) Nguyen, Tan Khoa; Eklund, Anders; Ohlsson, Henrik; Hernell, Frida; Ljung, Patric; Forsell, Camilla; Andersson, Mats; Knutsson, Hans; Ynnerman, Anders; Ruediger Westermann and Gordon Kindlmann
We present a novel approach to interactive and concurrent volume visualization of functional Magnetic Resonance Imaging (fMRI). While the patient is in the scanner, data is extracted in real-time using state-of-the-art signal processing techniques. The fMRI signal is treated as light emission when rendering a patient-specific high resolution reference MRI volume, obtained at the beginning of the experiment. As a result, the brain glows and emits light from active regions. The low resolution fMRI signal is thus effectively fused with the reference brain with the current transfer function settings yielding an effective focus and context visualization. The delay from a change in the fMRI signal to the visualization is approximately 2 seconds. The advantage of our method over standard 2D slice based methods is shown in a user study. We demonstrate our technique through experiments providing interactive visualization to the fMRI operator and also to the test subject in the scanner through a head mounted display.
Contour Nest: A Two-dimensional Representation for Three-dimensional Isosurfaces
(The Eurographics Association, 2006) Mizuta, Shinobu; Ono, Toshiki; Matsuda, Tetsuya; Raghu Machiraju and Torsten Moeller
Visualization of the topological structure of isosurfaces such as exclusion and inclusion plays an important role in analyzing three-dimensional (3D) scalar data like medical images, especially in selecting isosurfaces to observe. Under certain conditions, all isosurfaces in a 3D scalar field are closed surfaces having nest structure. Our purpose here is to translate closed isosurfaces in 3D space as a nest structure. Contour Tree (CT) can describe the nest structure among isosurfaces by tree structure, but it is difficult for users to understand the nest structure by direct observation of the tree shape. In this report, we propose a two-dimensional (2D) representation procedure named Contour Nest (CN) for intuitive display of the nest structure of isosurfaces. In the proposed method, nest structure of 3D isosurfaces extracted by Contour Tree is represented as 2D nest of rectangles. We have evaluated the effectiveness of the proposed method in selecting 3D isosurfaces.
Contour-Based Surface Reconstruction using Implicit Curve Fitting, and Distance Field Filtering and Interpolation
(The Eurographics Association, 2006) Marker, Jeffrey; Braude, Ilya; Museth, Ken; Breen, David; Raghu Machiraju and Torsten Moeller
This paper presents a volumetric approach to reconstructing a smooth surface from a sparse set of paral- lel binary contours, e.g. those produced via histologic imaging. It creates a volume dataset by interpolating 2D filtered distance fields. The zero isosurface embedded in the computed volume provides the desired result. MPU implicit functions are fit to the input contours, defined as binary images, to produce smooth curves with controllable error bounds. Full 2D Euclidean distance fields are then calculated from the implicit curves. A distance-dependent Gaussian filter is applied to the distance fields to smooth their medial axis discontinuities. Monotonicity-constraining cubic splines are used to construct smooth, blending slices between the input slices. A mesh that approximates the zero isosurface is then extracted from the resulting volume. The effectiveness of the approach is demonstrated on a number of complex, multi-component contour datasets.

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