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130
Efficient ray tracing of volume data
 ACM Transactions on Graphics
, 1990
"... Volume rendering is a technique for visualizing sampled scalar or vector fields of three spatial dimensions without fitting geometric primitives to the data. A subset of these techniques generates images by computing 2D projections of a colored semitransparent volume, where the color and opacity at ..."
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Cited by 325 (4 self)
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Volume rendering is a technique for visualizing sampled scalar or vector fields of three spatial dimensions without fitting geometric primitives to the data. A subset of these techniques generates images by computing 2D projections of a colored semitransparent volume, where the color and opacity at each point are derived from the data using local operators. Since all voxels participate in the generation of each image, rendering time grows linearly with the size of the dataset. This paper presents a fronttoback imageorder volumerendering algorithm and discusses two techniques for improving its performance. The first technique employs a pyramid of binary volumes to encode spatial coherence present in the data, and the second technique uses an opacity threshold to adaptively terminate ray tracing. Although the actual time saved depends on the data, speedups of an order of magnitude have been observed for datasets of useful size and complexity. Examples from two applications are given: medical imaging and molecular graphics.
C.H.: Visibility Preprocessing For Interactive Walkthroughs
 In: Computer Graphics (SIGGRAPH 91 Proceedings
, 1991
"... The number of polygons comprising interesting architectural models is many more than can be rendered at interactive frame rates. However, due to occlusion by opaque surfaces (e.g., walls), only a small fraction of atypical model is visible from most viewpoints. We describe a method of visibility pre ..."
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Cited by 281 (15 self)
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The number of polygons comprising interesting architectural models is many more than can be rendered at interactive frame rates. However, due to occlusion by opaque surfaces (e.g., walls), only a small fraction of atypical model is visible from most viewpoints. We describe a method of visibility preprocessing that is efficient andeffective foraxisaligned oril.ria / architectural m[}dels, A model is subdivided into rectangular cc//.$whose boundaries coincide with major opaque surfaces, Nonopaque p(~rtc~/.rare identified rm cell boundaries. and used to form ana~ju{~’n~y,q)f~/>//con nectingthe cells nfthesubdivisicm. Next. theccl/r/~cc/ / visibility is computed for each cell of the subdivisirrn, by linking pairs of cells between which unobstructed.si,q/~t/inr. ~exist. During an interactive ww/krhrm/,q/~phase, an observer with a known ~~sition and\it)M~~~)~t>mov esthrc>ughthe model. At each frame, the cell containingthe observer is identified, and the contents {]fp{>tentially visible cells areretrieved from storage. The set of potentially visible cells is further reduced by culling it against theobserver’s view cone, producing the ~)yt>r~]t(>// \ i,$ibi/ify, The contents of the remaining visible cells arc then sent to a graphics pipeline for hiddensurface removal and rendering, Tests onmoderatelyc mnplex 2D and 3D axial models reveal substantially reduced rendering loads,
Octrees for faster isosurface generation
 IEEE TRANSACTIONS ON MEDICAL IMAGING
, 2000
"... The large size of many volume data sets often prevents visualization algorithms from providing interactive rendering. The use of hierarchical data structures can ameliorate this problem by storing summary information to prevent useless exploration of regions of little or no current interest within ..."
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Cited by 274 (3 self)
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The large size of many volume data sets often prevents visualization algorithms from providing interactive rendering. The use of hierarchical data structures can ameliorate this problem by storing summary information to prevent useless exploration of regions of little or no current interest within the volume. This paper discusses research into the use of the octree hierarchical data structure when the regions of current interest can vary during the application, and are not known a priori. Octrees are well suited to the sixsided cell structure of many volumes. A new spaceefficient design is introduced for octree representations of volumes whose resolutions are not conveniently a power of two; octrees following this design are called branchonneed octrees (BONOs). Also, a caching method is described that essentially passes information between octree neighbors whose visitation times may be quite different, then discards it when its useful life is over. Using the application of octrees to isosurface generation as a focus, space and time comparisons for octreebased versus more traditional "marching" methods are presented.
Hierarchical Zbuffer visibility
 In Computer Graphics (SIGGRAPH ’93 Proceedings
, 1993
"... An ideal visibility algorithm should a) quickly reject most of the hidden geometry in a model and b) exploit the spatial and perhaps temporal coherence of the images being generated. Ray casting with spatial subdivision does well on criterion (a), but poorly on criterion (b). Traditional Zbuffer sc ..."
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Cited by 233 (1 self)
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An ideal visibility algorithm should a) quickly reject most of the hidden geometry in a model and b) exploit the spatial and perhaps temporal coherence of the images being generated. Ray casting with spatial subdivision does well on criterion (a), but poorly on criterion (b). Traditional Zbuffer scan conversion does well on criterion (b), but poorly on criterion (a). Here we present a hierarchical Zbuffer scanconversion algorithm that does well on both criteria. The method uses two hierarchical data structures, an objectspace octree and an imagespace Z pyramid, to accelerate scan conversion. The two hierarchical data structures make it possible to reject hidden geometry very rapidly while rendering visible geometry with the speed of scan conversion. For animation, the algorithm is also able to exploit temporal coherence. The method is well suited to models with high depth complexity, achieving orders of magnitude acceleration in some cases compared to ordinary Zbuffer scan conversion.
The radiance lighting simulation and rendering system
 In Proceedings of SIGGRAPH 94, ACM SIGGRAPH / ACM
, 1994
"... This paper describes a physicallybased rendering system tailored to the demands of lighting design and architecture. The simulation uses a lightbackwards raytracing method with extensions to efficiently solve the rendering equation under most conditions. This includes specular, diffuse and direct ..."
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Cited by 232 (4 self)
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This paper describes a physicallybased rendering system tailored to the demands of lighting design and architecture. The simulation uses a lightbackwards raytracing method with extensions to efficiently solve the rendering equation under most conditions. This includes specular, diffuse and directionaldiffuse reflection and transmission in any combination to any level in any environment, including complicated, curved geometries. The simulation blends deterministic and stochastic raytracing techniques to achieve the best balance between speed and accuracy in its local and global illumination methods. Some of the more interesting techniques are outlined, with references to more detailed descriptions elsewhere. Finally, examples are given of successful applications of this free software by others. CR Categories: I.3.3 [Computer Graphics]: Picture/image generation Display algorithms; I.3.7 [Computer Graphics]:
Volume Graphics
, 1993
"... this paper, is an emerging subfield of computer , s graphics concerned with the synthesis, manipulation, and rendering of volumetric objects tored in a volume buffer of voxels. Unlike volume visualization which focuses primarily on d g sampled and computed datasets, volume graphics is concerned prim ..."
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Cited by 148 (18 self)
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this paper, is an emerging subfield of computer , s graphics concerned with the synthesis, manipulation, and rendering of volumetric objects tored in a volume buffer of voxels. Unlike volume visualization which focuses primarily on d g sampled and computed datasets, volume graphics is concerned primarily with modele eometric scenes and particularly with those that are represented in a regular volume buffer a (see also the Glossary sidebar). As an approach, volume graphics has the potential to greatly dvance the field of 3D graphics by offering a comprehensive alternative to traditional surface F graphics. igure 1 portrays the taxonomy and the dataflow of volume visualization and volume graph  z ics. In this figure the use of volume graphics techniques in various stages of volume visuali ation is marked with solid lines. The major sources of volumetric data, displayed at the top, s are sampled/computed data (on the left) and geometric models (on the right). The ampled/computed input are 3D reconstructed to fill gaps of missing information and are then a g stored in the volume buffer. The geometric model in 3D continuous space is represented by eometric formula which is 3D scanconverted (voxelized) into a set of voxels that "best"  t approximate the model and is stored in the volume buffer (see [1] Chapter 5). The fundamen als of voxelization and the related 3D discrete topology issues are presented in the Fundamentals of Voxelization sidebar.  3  F
A Fast Voxel Traversal Algorithm for Ray Tracing
 In Eurographics ’87
, 1987
"... A fast and simple voxel traversal algorithm through a 3D space partition is introduced. Going from one voxel to its neighbour requires only two floating point comparisons and one floating point addition. Also, multiple ray intersections with objects that are in more than one voxel are eliminated. ..."
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Cited by 148 (5 self)
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A fast and simple voxel traversal algorithm through a 3D space partition is introduced. Going from one voxel to its neighbour requires only two floating point comparisons and one floating point addition. Also, multiple ray intersections with objects that are in more than one voxel are eliminated. Introduction In recent years, ray tracing has become the algorithm of choice for generating high fidelity images. Its simplicity and elegance allows one to easily model reflection, refraction and shadows. 1 Unfortunately, it has a major drawback: computational expense. The prime reason for this is that the heart of ray tracing, intersecting an object with a ray, is expensive and can easily take up to 95% of the rendering time. Unless some sort of intersection culling is performed, each ray must intersect all the objects in the scene, a very expensive proposition. There are two general strategies for intersection culling: hierarchical bounding volumes 1, 2, 3, 4 and space partitioning...
Multilevel ray tracing algorithm
 ACM Trans. on Graphics
, 2005
"... We propose new approaches to ray tracing that greatly reduce the required number of operations while strictly preserving the geometrical correctness of the solution. A hierarchical “beam” structure serves as a proxy for a collection of rays. It is tested against a kdtree representing the overall sc ..."
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Cited by 124 (2 self)
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We propose new approaches to ray tracing that greatly reduce the required number of operations while strictly preserving the geometrical correctness of the solution. A hierarchical “beam” structure serves as a proxy for a collection of rays. It is tested against a kdtree representing the overall scene in order to discard from consideration the subset of the kdtree (and hence the scene) that is guaranteed not to intersect with any possible ray inside the beam. This allows for all the rays inside the beam to start traversing the tree from some node deep inside thus eliminating unnecessary operations. The original beam can be further subdivided, and we can either continue looking for new optimal entry points for the subbeams, or we can decompose the beam into individual rays. This is a hierarchical process that can be adapted to the geometrical complexity of a particular view direction allowing for efficient geometric antialiasing. By amortizing the cost of partially traversing the tree for all the rays in a beam, up to an order of magnitude performance improvement can be achieved enabling interactivity for complex scenes on ordinary desktop machines.
A survey of shadow algorithms
 IEEE Computer Graphics and Applications
, 1990
"... Essential to realistic and visually appealing images, shadows are difficult ta compute in most display environments. This survey characterizes the various types of shadows. It also describes most existing shadow algorithms and discusses their complexities, advantages, and shommings. We examine herd ..."
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Cited by 123 (3 self)
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Essential to realistic and visually appealing images, shadows are difficult ta compute in most display environments. This survey characterizes the various types of shadows. It also describes most existing shadow algorithms and discusses their complexities, advantages, and shommings. We examine herd shadows, soft shadbws, shadows of transparent objects, and shadows for complex modeling primitives. For each type, we examine shadow algorithms within various rendswing techniques. This survey attempts to provide readem with enough background and insight on the various rmthods to dow them to choose the algorithm best wpuited to their W. We also hope that our analysis will h&p identify the a m that need more research and point bo possible sotutkms. A shadowa region of relative darkness within an not necessarily attenuate the light it occludes. In fact, illuminated regionoccurs when an object totally or it can concentrate light. However, as is traditional in partially occludes the light. A transparent object does image synthesis, lve will consider a region to be in
Fast ray tracing by ray classification
 In Proceedings of the 14th Annual Conference on Computer Graphics and Interactive Techniques
, 1987
"... We describe a new approach to ray tracing which drastically reduces the number of rayobject and raybounds intersection calculations by means of 5dimensional space subdivision. Collections of rays originating from a common 3D rectangular volume and directed through a 2D solid angle are represented ..."
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Cited by 109 (7 self)
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We describe a new approach to ray tracing which drastically reduces the number of rayobject and raybounds intersection calculations by means of 5dimensional space subdivision. Collections of rays originating from a common 3D rectangular volume and directed through a 2D solid angle are represented as hypercubes in 5space. A 5D volume bounding the space of rays is dynamically subdivided into hypercubes, each linked to a set of objects which are candidates for intersection. Rays are classified into unique hypercubes and checked for intersection with the associated candidate object set. We compare several techniques for object extent testing, including boxes, spheres, planesets, and convex polyhedra. In addition, we examine optirnizations made possible by the directional nature of the algorithm, such as sorting, caching and backface culling. Results indicate that this algorithm significantly outperforms previous ray tracing techniques, especially for complex environments.