Volumetric Ray Casting Research Articles

Volumetric Rendering on Wavelet-Based Adaptive Grid

Numerical modeling of physical phenomena frequently involves processes across a wide range of spatial and temporal scales. In the last two decades, the advancements in wavelet-based numerical methodologies to solve partial differential equations, combined with the unique properties of wavelet analysis to resolve localized structures of the solution on dynamically adaptive computational meshes, make it feasible to perform large-scale numerical simulations of a variety of physical systems on a dynamically adaptive computational mesh that changes both in space and time. Volumetric visualization of the solution is an essential part of scientific computing, yet the existing volumetric visualization techniques do not take full advantage of multi-resolution wavelet analysis and are not fully tailored for visualization of a compressed solution on the wavelet-based adaptive computational mesh. Our objective is to explore the alternatives for the visualization of time-dependent data on space-time varying adaptive mesh using volume rendering while capitalizing on the available sparse data representation. Two alternative formulations are explored. The first one is based on volumetric ray casting of multi-scale datasets in wavelet space. Rather than working with the wavelets at the finest possible resolution, a partial inverse wavelet transform is performed as a preprocessing step to obtain scaling functions on a uniform grid at a user-prescribed resolution. As a result, a solution in physical space is represented by a superposition of scaling functions on a coarse regular grid and wavelets on an adaptive mesh. An efficient and accurate ray casting algorithm is based just on these coarse scaling functions. Additional details are added during the ray tracing by taking an appropriate number of wavelets into account based on support overlap with the interpolation point, wavelet coefficient magnitude, and other characteristics, such as opacity accumulation (front to back ordering) and deviation from frontal viewing direction. The second approach is based on complementing of wavelet-based adaptive mesh to the traditional Adaptive Mesh Refinement (AMR) mesh. Both algorithms are illustrated and compared to the existing volume visualization software for Rayleigh-Benard thermal convection and electron density data sets in terms of rendering time and visual quality for different data compression of both wavelet-based and AMR adaptive meshes.

Visualizing 3D atmospheric data with spherical volume texture on virtual globes

Volumetric ray-casting is a widely used algorithm in volume visualization, but implementing this algorithm to render atmospheric volume data that cover a large area on virtual globes constitutes a challenging problem. Because atmospheric data are usually georeferenced to a spherical coordinate system described by longitude, latitude and altitude, adaptations to the conventional volumetric ray-casting method are needed to accommodate spherical volume texture sampling. In this paper, we present a volumetric ray-casting framework to visualize atmospheric data that cover a broad but thin geographic area (because of the thinness of Earth׳s atmosphere). Volume texture conforming to the spherical coordinate system of a virtual globe can be created directly from the spherical volume data to avoid oversampling, undersampling or a loss of accuracy due to reprojecting and resampling such data into a Cartesian coordinate system. Considering the insignificant physical thickness of the atmosphere of the Earth, the ray-casting method presented in this paper also allows for real-time vertical scaling (exaggeration of the altitudinal range) without the need to re-process the volume texture, enabling convenient visual observation of the altitudinal variations. The spherical volume ray-casting method is implemented in a deferred rendering framework to integrate the volume effects into a virtual globe composed of a variety of background geospatial data objects, such as terrain, imagery, vector shapes and 3D geometric models.

Context Preserving Maps of Tubular Structures

When visualizing tubular 3D structures, external representations are often used for guidance and display, and such views in 2D can often contain occlusions. Virtual dissection methods have been proposed where the entire 3D structure can be mapped to the 2D plane, though these will lose context by straightening curved sections. We present a new method of creating maps of 3D tubular structures that yield a succinct view while preserving the overall geometric structure. Given a dominant view plane for the structure, its curve skeleton is first projected to a 2D skeleton. This 2D skeleton is adjusted to account for distortions in length, modified to remove intersections, and optimized to preserve the shape of the original 3D skeleton. Based on this shaped 2D skeleton, a boundary for the map of the object is obtained based on a slicing path through the structure and the radius around the skeleton. The sliced structure is conformally mapped to a rectangle and then deformed via harmonic mapping to match the boundary placement. This flattened map preserves the general geometric context of a 3D object in a 2D display, and rendering of this flattened map can be accomplished using volumetric ray casting. We have evaluated our method on real datasets of human colon models.

B104 ボリュームレンダリングにおける照明の最適配置

Locating an optimal light source is an important task for image synthesis because it influences the spatial perception of the observers. Several methods have been proposed, that search for the optimal location of light sources for 3D surfaces, but none has been done for volumes. This paper presents a new method for finding an optimal location of a single parallel light source for volumetric ray-casting. The method computes the entropy of brightness distribution of representative isosurfaces. The method then utilizes the opacity transfer function to assign a distinct weight to each of the values of isosurface illumination entropy to evaluate the plausible illuminating entropy for the volume. The light with the maximum entropy value allows the observers to realize the volume features with enriched 3D visual cues.

Volume visualization of multicolor laser confocal microscope data

The objective of this work is to give biologists the ability to visualize multicolor laser confocal microscope (MLCM) data sets. We present the application of volume ray casting techniques to create fast and accurate visualization of the spatial structures in MLCM data sets. We provide various volume pre-processing routines for noise removal, smoothing and edge enhancement. The tool has an interactive interface to assist the operator in classifying the volume using various transparency mappings. We have developed volume rendering using volumetric ray casting based upon a perspective camera model. We illustrate an innovative way to simultaneously visualize LCM data set from three lasers using voxel level merging. A method to generate key frame animation sequence of an arbitrary fly through path is also included in the visualization tool.

Three-dimensional brain visualization for metachromatic leukodystrophy

The basic understanding of many neurogenetic diseases requires study of the clinical, biochemical, and pathological aspects. To study the pathological aspects, the organs affected by the disease must be observed. We have used volume visualization techniques to create three-dimensional (3D) brain images of a patient with late infantile metachromatic leukodystrophy (MLD). The 3D brain images showed clearly, stereographically, and non-invasively the intracerebral lesion. This lesion, which indicated hyperintensity in magnetic resonance (MR) images, extended throughout the periventricular white matter. The 3D brain images are provided to integrate information. Volumetric ray-casting was useful in obtaining directly images of the entire brain and in allowing an intuitive understanding of the extension of the lesion in three dimensions and of the extent of the defects in the MLD brain. Isosurfacing facilitated a clear extraction of the lesion located by volumetric ray-casting. Each technique used in this study played a role in visualization and their use was complementary. 3D brain images will promote morphological investigation of neurogenetic diseases.