VG05: Eurographics/IEEE VGTC Workshop on Volume Graphics 2005

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https://diglib7.eg.org/handle/10.2312/472

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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.
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.
End-to-End Data Reduction and Hardware Accelerated Rendering Techniques for Visualizing Time-Varying Non-uniform Grid Volume Data
(The Eurographics Association, 2005) Akiba, Hiroshi; Ma, Kwan-Liu; Clyne, John; Klaus Mueller and Thomas Ertl and Eduard Groeller
We present a systematic approach for direct volume rendering terascale-sized data that are time-varying, and possibly non-uniformly sampled, using only a single commodity graphics PC. Our method employs a data reduction scheme that combines lossless, wavelet-based progressive data access with a user-directed, hardware-accelerated data packing technique. Data packing is achieved by discarding data blocks with values outside the data interval of interest and encoding the remaining data in a structure that can be efficiently decoded in the GPU. The compressed data can be transferred between disk, main memory, and video memory more efficiently, leading to more effective data exploration in both spatial and temporal domains. Furthermore, our texture-map based volume rendering system is capable of correctly displaying data that are sampled on a stretched, Cartesian grid. To study the effectiveness of our technique we used data sets generated from a large solar convection simulation, computed on a non-uniform, 504x504x2048 grid.
An Evaluation of Using Real-time Volumetric Display of 3D Ultrasound Data for Intracardiac Catheter Manipulation Tasks
(The Eurographics Association, 2005) Wang, Aaron S.; Narayan, Girish; Kao, David; Liang, David; Klaus Mueller and Thomas Ertl and Eduard Groeller
The enthusiasm for novel, minimally invasive, catheter based intracardiac procedures has highlighted the need to provide accurate, real-time, anatomically based image guidance to decrease complications, improve precision, and decrease fluoroscopy time. The recent development of real-time 3D echocardiography creates the opportunity to greatly improve our ability to guide minimally invasive procedures [Ahm03]. However, the need to present 3D data on a 2D display decreases the utility of 3D echocardiography because echocardiographers cannot readily appreciate 3D perspective on a 2D display without ongoing image manipulation. We evaluated the use of a novel strategy of presenting the data in a true 3D volumetric display, Perspecta Spatial 3D System (Actuality Systems, Inc., Burlington, MA). Two experienced echocardiographers performed the task of identifying the targeted location of a catheter within 6 different phantoms using four display methods. Echocardiographic images were obtained with a SONOS 7500 (Philips Medical Systems, Inc., Andover, MA). Completion of the task was significantly faster with the Perspecta display with no loss in accuracy. Echocardiography in 3D significantly improves the ability of echocardiography for guidance of catheter based procedures [Ahm03]. Further improvement is achieved by using a true 3D volumetric display, which allows for more intuitive assessment of the spatial relationships of catheters in three-dimensional space compared with conventional 2D visualization modalities.
GPU Accelerated Image Aligned Splatting
(The Eurographics Association, 2005) Neophytou, Neophytos; Mueller, Klaus; Klaus Mueller and Thomas Ertl and Eduard Groeller
Splatting is a popular technique for volume rendering, where voxels are represented by Gaussian kernels, whose pre-integrated footprints are accumulated to form the image. Splatting has been mainly used to render pre-shaded volumes, which can result in significant blurring in zoomed views. This can be avoided in the image-aligned splatting scheme, where one accumulates kernel slices into equi-distant, parallel sheet buffers, followed by classification, shading, and compositing. In this work we attempt to evolve this algorithm to the next level: GPU based acceleration. First we describe the challenges that the highly parallel Gather architecture of modern GPUs poses to the Scatter based nature of a splatting algorithm. We then describe a number of strategies that exploit newly introduced features of the latest-generation hardware to address these limitations. Two crucial operations to boost the performance in image-aligned splatting are the early elimination of hidden splats and the skipping of empty buffer-space. We will describe mechanisms which take advantage of the early z-culling hardware facilities to accomplish both of these operations efficiently in hardware.
GPU-based Object-Order Ray-Casting for Large Datasets
(The Eurographics Association, 2005) Hong, Wei; Qiu, Feng; Kaufman, Arie; Klaus Mueller and Thomas Ertl and Eduard Groeller
We propose a GPU-based object-order ray-casting algorithm for the rendering of large volumetric datasets, such as the Visible Human CT datasets. A volumetric dataset is decomposed into small sub-volumes, which are then organized using a min-max octree structure. The small sub-volumes are stored in the leaf nodes of the min-max octree, which are also called cells. The cells are classified using a transfer function, and the visible cells are then loaded into the video memory or the AGP memory. The cells are sorted and projected onto the image plane front to back. The cell projection is implemented using a volumetric ray-casting algorithm on the GPU. In order to make the cell projection more efficient, we devise a propagation method to sort cells into layers. The cells within the same layer are projected at the same time. We demonstrate the efficiency of our algorithm using the Visible Human datasets and a segmented photographic brain dataset on commodity PCs.
An Integrated Pipeline of Decompression, Simplification and Rendering for Irregular Volume Data
(The Eurographics Association, 2005) Yang, Chuan-Kai; Chiueh, Tzi-Cker; Klaus Mueller and Thomas Ertl and Eduard Groeller
Very large irregular-grid volume data sets are typically represented as tetrahedral mesh and require substantial disk I/O and rendering computation. One effective way to reduce this demanding resource requirement is compression. Previous research showed how rendering and decompression of a losslessly compressed irregular-grid data set can be integrated into a one-pass computation. This work advances the state of the art one step further by showing that a losslessly compressed irregular volume data set can be simplified while it is being decompressed and that simplification, decompression, and rendering can again be integrated into a pipeline that requires only a single pass through the data sets. Since simplification is a form of lossy compression, the on-the-fly volume simplification algorithm provides a powerful mechanism to dynamically create versions of a tetrahedral mesh at multiple resolution levels directly from its losslessly compressed representation, which also corresponds to the finest resolution level. In particular, an irregular-grid volume renderer can exploit this multi-resolution representation to maintain interactivity on a given hardware/software platform by automatically adjusting the amount of rendering computation that could be afforded, or performing so called time-critical rendering. The proposed tetrahedral mesh simplification algorithm and its integration with volume decompression and rendering has been successfully implemented in the Gatun system. Performance measurements on the Gatun prototype show that simplification only adds less than 5% of performance overhead on an average and with multi-resolution pre-simplification the end-to-end rendering delay indeed decreases in an approximately linear fashion with respect to the simplification ratio.
Introducing Topological Attributes for Objective-Based Visualization of Simulated Datasets
(The Eurographics Association, 2005) Takeshima, Yuriko; Takahashi, Shigeo; Fujishiro, Issei; Nielson, Gregory M.; Klaus Mueller and Thomas Ertl and Eduard Groeller
Recent development in the design of multi-dimensional transfer functions allows us to automatically generate comprehensible visualization images of given volumes by taking into account local features such as differentials and curvatures. However, especially when visualizing volumes obtained by scientific simulations, observers usually exploit their knowledge about the simulation settings as the clues to the effective control of visualization parameters for their own specific purposes. This paper therefore presents an objective-based framework for visualizing simulated volume datasets by introducing a new set of topological attributes. These topological attributes are calculated from the level-set graph of a given volume dataset, and thus differ from the conventional local attributes in that they also illuminate the global structure of the volume. The present framework provides a systematic means of emphasizing the underlying volume features, such as nested structures of isosurfaces, configuration of isosurface trajectories, and transitions of isosurface's topological type. Several combinations of the topological attributes together with the associated transfer function designs are devised and applied to real simulated datasets in order to demonstrate the feasibility of the present framework.
iSBVR: Isosurface-aided Hardware Acceleration Techniques for Slice-Based Volume Rendering
(The Eurographics Association, 2005) Xue, Daqing; Zhang, Caixia; Crawfis, Roger; Klaus Mueller and Thomas Ertl and Eduard Groeller
In this paper, we examine the performance of the early z-culling feature on current high-end commodity graphics cards and present an isosurface-aided hardware acceleration algorithm for slice-based volume rendering (iSBVR) to maximize its utilization. We analyze the computational models for early z-culling of the texture based volume rendering. We demonstrate that the performance improves with two to four times speedup against an original straightforward SBVR on an ATI 9800 pro display board. As volumetric shaders become increasingly complex, the advantages of fast z-culling will become even more pronounced.
A Multiresolution Volume Rendering Framework for Large-Scale Time-Varying Data Visualization
(The Eurographics Association, 2005) Wang, Chaoli; Gao, Jinzhu; Li, Liya; Shen, Han-Wei; Klaus Mueller and Thomas Ertl and Eduard Groeller
We present a new parallel multiresolution volume rendering framework for large-scale time-varying data visualization using the wavelet-based time-space partitioning (WTSP) tree. Utilizing the wavelet transform, a largescale time-varying data set is converted into a space-time multiresolution data hierarchy, and is stored in a timespace partitioning (TSP) tree. To eliminate the parent-child data dependency for reconstruction and achieve loadbalanced rendering, we design an algorithm to partition the WTSP tree and distribute the wavelet-compressed data along hierarchical space-filling curves with error-guided bucketization. At run time, the WTSP tree is traversed according to the user-specified time step and tolerances of both spatial and temporal errors. Data blocks of different spatio-temporal resolutions are reconstructed and rendered to compose the final image in parallel. We demonstrate that our algorithm can reduce the run-time communication cost to a minimum and ensure a well-balanced workload among processors when visualizing gigabytes of time-varying data on a PC cluster.
Representation of Objects with Sharp Details in Truncated Distance Fields
(The Eurographics Association, 2005) Novotný, Pavol; Srámek, Milos; Klaus Mueller and Thomas Ertl and Eduard Groeller
We present a new approach for voxelization of implicit solids which contain sharp details. If such objects are processed by common techniques, voxelization artifacts may appear, resulting, among others, in jaggy edges in rendered images. To cope with this problem we proposed a technique called Sharp Details Correction. The main idea is to modify objects during the process of voxelization according to the representability criterion. This means that sharp edges end vertices are rounded to a curvature, which depends on the grid resolution. Thus, we obtain artifact-free voxelized solids which produce alias-free images.
Robust Generation of Signed Distance Fields from Triangle Meshes
(The Eurographics Association, 2005) Bærentzen, J. Andreas; Klaus Mueller and Thomas Ertl and Eduard Groeller
A new method for robust generation of distance fields from triangle meshes is presented. Graphics hardware is used to accelerate a technique for generating layered depth images. From multiple layered depth images, a binary volume and a point representation are extracted. The point information is then used to convert the binary volume into a distance field. The method is robust and handles holes, spurious triangles and ambiguities. Moreover, the method lends itself to boolean operations between solids. Since a point cloud as well as a signed distance is generated, it is possible to extract an iso-surface of the distance field and fit it to the point set. Using this method, one may recover sharp edge information. Examples are given where the method for generating distance fields coupled with mesh fitting is used to perform boolean and morphological operations on triangle meshes. [volume graphics] [layered depth image] [distance field]
Scaffolding-based Segmentation of Coronary Vascular Structures
(The Eurographics Association, 2005) Bartz, Dirk; Lakare, Sarang; Klaus Mueller and Thomas Ertl and Eduard Groeller
The coronary arteries are essential for the proper function of the human heart. However, they are generally difficult to segment in volume datasets separately from the other blood-filled cavities of the heart. The major reason for these difficulties is the lack of sufficient spatial resolution and partial volume effects. In this paper, we present a method to mark the coronary arteries by a virtual endoscopic traversal. Virtual endoscopy enables a significantly easier visual identification of the blood vessels in comparison to outside views or slice-by-slice examination methods. Furthermore, we use this marking as a scaffold for the actual segmentation of the coronary arteries.
A Simple and Flexible Volume Rendering Framework for Graphics-Hardware-based Raycasting
(The Eurographics Association, 2005) Stegmaier, Simon; Strengert, Magnus; Klein, Thomas; Ertl, Thomas; Klaus Mueller and Thomas Ertl and Eduard Groeller
In this work we present a flexible framework for GPU-based volume rendering. The framework is based on a single pass volume raycasting approach and is easily extensible in terms of new shader functionality. We demonstrate the flexibility of our system by means of a number of high-quality standard and non-standard volume rendering techniques. Our implementation shows a promising performance in a number of benchmarks while producing images of higher accuracy than obtained by standard pre-integrated slice-based volume rendering.
Simplification of Unstructured Tetrahedral Meshes by Point Sampling
(The Eurographics Association, 2005) Uesu, Dirce; Bavoil, Louis; Fleishman, Shachar; Shepherd, Jason; Silva, Cláudio T.; Klaus Mueller and Thomas Ertl and Eduard Groeller
Tetrahedral meshes are widely used in scientific computing for representing three-dimensional scalar, vector, and tensor fields. The size and complexity of some of these meshes can limit the performance of many visualization algorithms, making it hard to achieve interactive visualization. The use of simplified models is one way to enable the real-time exploration of these datasets. In this paper, we propose a novel technique for simplifying large unstructured meshes. Most current techniques simplify the geometry of the mesh using edge collapses. Our technique simplifies an underlying scalar field directly by segmenting the original scalar field into two pieces: the boundary of the original domain and the interior samples of the scalar field. We then simplify each piece separately, taking into account proper error bounds. Finally, we combine the simplified domain boundary and scalar field into a complete, simplified mesh that can be visualized with standard unstructured-data visualization tools. Our technique is much faster than edge-collapse-based simplification approaches. Furthermore, it is particularly suitable for aggressive simplification. Experiments show that isosurfaces and volume renderings of meshes produced by our technique have few noticeable visual artifacts.
A Simplified Model for Inhomogeneous Subsurface Scattering
(The Eurographics Association, 2005) Sharp, Richard; Machiraju, Raghu; Klaus Mueller and Thomas Ertl and Eduard Groeller
In recent years there has been considerable interest in modeling realistic subsurface light scattering in materials such as marble, human skin, or clouds. Many of these models provide a solution for the transport equation in a homogeneous or layered scattering media. The model we present here exploits a diffusion mechanism to provide a simpler solution to the transport equation. Treating light flux as current we can use circuit analysis techniques and linear systems to solve directly for the steady state transport equation and ignore the transient values. Thus our model can simulate light transport in heterogeneous materials and complex geometry.
Texturing and Hypertexturing of Volumetric Objects
(The Eurographics Association, 2005) Miller, Chris M.; Jones, Mark W.; Klaus Mueller and Thomas Ertl and Eduard Groeller
Texture mapping is an extremely powerful and flexible tool for adding complex surface detail to an object. This paper introduces a method of surface texturing and hypertexturing complex volumetric objects in real-time. We employ distance field volume representations, texture based volume rendering and procedural texturing techniques with Shader Model 2.0 flexible programmable graphics hardware. We aim to provide a flexible cross-platform, non vendor specific implementation.
Time-Varying Interval Volumes
(The Eurographics Association, 2005) Zhang, Caixia; Xue, Daqing; Crawfis, Roger; Wenger, Rephael; Klaus Mueller and Thomas Ertl and Eduard Groeller
In this paper, we study the interval segmentation and direct rendering of time-varying volumetric data to provide a more effective and interactive volume rendering of time-varying structured and unstructured grids. Our segmentation is based upon intervals within the scalar field between time steps, producing a set of geometrically defined time-varying interval volumes. To construct the time-varying interval volumes, we cast the problem one dimension higher, using a five-dimensional iso-contour construction for interactive computation or segmentation. The key point of this paper is how to render the time-varying interval volumes directly. We directly render the 4D interval volumes by projecting the 4D simplices onto 3D, decomposing the projected 4-simplices to 3-simplices and then rendering them using a modified hardware-implemented projected tetrahedron method. In this way, we can see how interval volumes change with the time in one view. The algorithm is independent of the topology of the polyhedral cells comprising the grid, and thus offers an excellent enhancement to the volume rendering of time-varying unstructured grids. Another advantage of this algorithm is that various volumetric and surface boundaries can be embedded into the time-varying interval volumes.
A Virtual Reality Toolkit for the Diagnosis and Monitoring of Myocardial Infarctions
(The Eurographics Association, 2005) Ryan, John; O Sullivan, Carol; Bell, Christopher; Mulvihill, Niall; Klaus Mueller and Thomas Ertl and Eduard Groeller
We have developed a software system that takes standard electrocardiogram (ECG) input and interprets this input along with user-defined and automatically defined markers to diagnose myocardial infarctions (MI). These pathologies are then automatically represented within a volumetric model of the heart. Over a period of six months 30 patients were monitored using a digital ECG system and this information was used to test and develop our system. It was found that the STEMIs (ST segment Elevation MI) were successfully diagnosed, however NSTEMIs (Non-STEMI), although correctly interpreted, were more ambiguous due to the fact that T wave inversions are sometimes seen on normal ECGs. Control ECGs of normal hearts were also taken. The system correctly interpreted this data as being normal. A standard voxel-count metric was developed so that future work in MI monitoring will be possible. The toolkit was found to be beneficial for three possible uses, as a diagnostic tool for clinicians, as a teaching tool for students and also as an information tool for the patient.
Visualization of Time-Varying Volumetric Data using Differential Time-Histogram Table
(The Eurographics Association, 2005) Younesy, Hamid; Möller, Torsten; Carr, Hamish; Klaus Mueller and Thomas Ertl and Eduard Groeller
We introduce a novel data structure called Differential Time-Histogram Table (DTHT) for visualization of timevarying scalar data. This data structure only stores voxels that are changing between time-steps or during transfer function updates. It allows efficient updates of data necessary for rendering during a sequence of queries common during data exploration and visualization. The table is used to update the values held in memory so that efficient visualization is supported while guaranteeing that the scalar field visualized is within a given error tolerance of the scalar field sampled. Our data structure allows updates of time-steps in the order of tens of frames per second for volumes of sizes of 4.5GB, enabling real-time time-sliders.

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