R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12:19#28, 1992.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....Thus the correctness of isosurfaces with normals are dependent on the densities of incident voxels of all intersecting edges, and their 6 neighbors. In addition to indirect volume rendering, we take into account direct volume rendering. In particular, we focus on the ray casting algorithm [7, 14]. While our method is designed for ray casting, it is easily modified for other popular volume rendering methods such as splatting. When a ray is cast, the shaded color opacity pairs are computed at resampling points on the ray, and are accumulated in front to back order. In classifying materials, ....

R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12(5): 19

....areas. One of the most frequently applied techniques for visual ization is direct volume rendering, which produces 3D rendered images of high quality, directly from volume data. Splatting [20, 21] is a popular direct volume rendering method, which is widely used along with ray casting [9, 19, 23] and shear warping [7] It has been originally introduced as an object order algorithm, while the splatting computation can also be performed in image order [14] In the objectorder splatting approach, voxels are traversed in either front to backorback to front order consistent with a given view ....

R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12(5):19--28, Sept. 1992. 27

....[9] so that the use of a distance map for surface normal calculation is not necessary. However, as discussed in Section 5, there are times when a binary segmentation of the grey scale data is preferable for surface shading. Some existing methods store surface normals of known analytic models [32] or polygonal models [17] at each data point. These sampled surface normals are used to reconstruct normals for samples between data elements during rendering. However, this method requires the storage of 3 floating point values per data element or quantization of the surface normals, which can ....

R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12:19--28, 1992.

....next location until the ray passes completely through the data set. Each incremental position of the ray is termed a sample point at which an intersection test is performed against the data set. This approach is similar to discrete ray tracing, which also uses volume data, and is presented in [Yagel92] Discrete ray tracing first converts 3D geometric data into voxels and combines them to make a single volume data set. During this stage all view point independent attributes of the voxels are also calculated. A line drawing algorithm based on Bresenham s algorithm [Foley89] is then used for ....

Roni Yagel, Daniel Cohen, and Arie Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12(5):19--28, September 1992.

....and visualizing dynamic datasets. Furthermore, 3D double buffering follows the development of the traditional graphics pipeline (i.e. double buffered frame buffer) These are areas for additional research. If volume graphics is to offset traditional polygonal graphics, volumetric raytracing [48] and perspective projections must be considered. Raytracing is capable of producing photo realistic images using shadows, reflection, refraction, etc. For instance, VIRIM is capable of shadows. Secondary rays during raytracing have less coherence than primary rays, therefore, volumetric raytracing ....

R. Yagel, D. Cohen, and A. Kaufman. Discrete Ray Tracing. IEEE Computer Graphics and Applications, 12(9):19--28, September 1992.

....geometrically. The sources of volume data are either sampled data of real objects (e.g. CT of human organs) produced by a computer simulation (e.g. computational fluid dynamics running on a supercomputer) or synthesized by voxelizing a geometric model (e.g. CAD of mechanical parts [YCK92] Volume visualization is concerned with the representation, manipulation, and rendering of such datasets. A volumetric dataset is commonly represented as a sequence of cross sections or a volume buffer which is a 3D integer grid of unit volume cells called voxels. Each voxel is a quantum unit ....

....VolVis contains several rendering algorithms. One is a low accuracy rendering algorithm employed by the volumetric navigator, which allows the user to manipulate the data and change viewing parameters with a high degree of interactivity. At the other end is a volumetric ray tracer (e.g. YCK92] which provides realistic images at the cost of high rendering times. By placing restrictions on the viewing parameters, a template based ray caster [YK92] can be employed to produce more accurate images than the navigator at lower rendering times than the volumetric ray tracer. Another ....

R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12(5):19--28, September 1992.

....every cell will be visited by at least one ray. A second approach is to calculate the entry and exist points for each cell. The integrated intensity through the cell can then be calculated and composited into the image. Algorithms for efficiently stepping through a regular grid are described in [1, 84, 86, 105, 106]. Garrity [28] presents an algorithm for tracing through unstructured meshes. Ray tracing usually proceeds from the eye point into the mesh. This requires that the accumulated opacity be saved as the ray progresses. If the opacity reaches one, implying that no light further along the ray will ....

....ray will reach the viewer, then the ray can be terminated early. Levoy [53, 54] uses this technique for calculating contour surfaces. Yagel and Shi [107] illustrate a technique to preprocess the volume data such that opaque surfaces are quickly intersected when ray tracing. Many other techniques [11 14, 48 52, 55, 68, 70, 90, 94, 105, 106] have been developed to accelerate or extend the ray tracing of volume densities. 15 A A Figure 3 2. Common Tetrahedral Projections 3.3 Cell Projection Cell projection methods are precisely what their name implies. They project each face of a cell onto the image plane. The faces of a ....

Yagel, R., D. Cohen, and A. Kaufmann, Discrete Ray Tracing. IEEE Computer Graphics and Applications, Sept. 1992. 12(5): p. 19-28.

....process, one being ray casting [13] Ray casting is similar to ray tracing, except that in ray casting rays travel through the data set once without creating reflection rays. The ray casting used in this system is based on discrete increments along each ray similar to discrete ray tracing [18]. As the rays travel through the data, sample points are extracted and used to calculate local gradients surrounding the sample point which is used in opacity calculations to combine the sample points to create the final pixel value. The shading of the surface is calculated using either the ....

YAGEL, R., COHEN, D., AND KAUFMAN, A. Discrete ray tracing. IEEE Computer Graphics and Applications 12, 5 (September 1992), 19--28. (a) (b)

....lighting model (like the one just presented) and compositing the samples as described in the previous section. This method is very flexible and extremely easy to implement. There are several extensions of basic ray casting to include higher order illumination effects, like discrete ray tracing [131], and volumetric ray tracing [117] Both of these techniques take into account global illumination effects incorporating more accurate approximations of the more general rendering equation [50] Because of the large size of volumes, volumetric ray casting (and ray tracing) is very expensive. ....

R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, pages 19--28, 1992. BIBLIOGRAPHY 167

....graphics have investigated algorithms for rendering non diffuse synthetic scenes from their volumetric representation. Volumetric ray tracing [19, 31] can be used for this purpose, handling specular reflections and other nondiffuse phenomena via recursive tracing of secondary rays. Yagel et al. [33] describe discrete ray tracing, a technique in which discrete (voxelized) rays are tracked through the 3D volume buffer until they encounter a voxel occupied by a voxelized surface. Our proposed approach utilizes a related technique, which traces a ray in a layered depth projection of the scene. ....

....the projection axis of each LDI, whereas a volume buffer is not capable of resolving cases where two or more surfaces occupy the same voxel. 3. Similarly to image based ray tracing, it is possible to render images of non diffuse scenes by recursively tracing discrete rays in the 3D volume buffer [33]. In our representation, the LLF lets us eliminate the recursion altogether, or terminate it after a small number of reflections. 4 Computational elements for rendering 4.1 3D warping Rendering begins by 3D warping the view independent LDIs in order to generate a primary image of the scene. This ....

Roni Yagel, Daniel Cohen, and Arie Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12(5):19--28, September 1992.

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R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12:19#28, 1992.

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R. Yagel, D. Cohen, and A. Kaufman. Discrete ray tracing. IEEE Computer Graphics and Applications, 12:19#28, 1992.

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