Showing papers on "Ray tracing (graphics) published in 1994"

The RADIANCE lighting simulation and rendering system

Abstract: This paper describes a physically-based rendering system tailored to the demands of lighting design and architecture. The simulation uses a light-backwards ray-tracing method with extensions to efficiently solve the rendering equation under most conditions. This includes specular, diffuse and directional-diffuse reflection and transmission in any combination to any level in any environment, including complicated, curved geometries. The simulation blends deterministic and stochastic ray-tracing 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.

Generalization of Lambert's reflectance model

Abstract: Lambert's model for body reflection is widely used in computer graphics. It is used extensively by rendering techniques such as radiosity and ray tracing. For several real-world objects, however, Lambert's model can prove to be a very inaccurate approximation to the body reflectance. While the brightness of a Lambertian surface is independent of viewing direction, that of a rough surface increases as the viewing direction approaches the light source direction. In this paper, a comprehensive model is developed that predicts body reflectance from rough surfaces. The surface is modeled as a collection of Lambertian facets. It is shown that such a surface is inherently non-Lambertian due to the foreshortening of the surface facets. Further, the model accounts for complex geometric and radiometric phenomena such as masking, shadowing, and interreflections between facets. Several experiments have been conducted on samples of rough diffuse surfaces, such as, plaster, sand, clay, and cloth. All these surface demonstrate significant deviation from Lambertian behavior. The reflectance measurements obtained are in strong agreement with the reflectance predicted by the model.

Priority rendering with a virtual reality address recalculation pipeline

Abstract: Virtual reality systems are placing never before seen demands on computer graphics hardware, yet few graphics systems are designed specifically for virtural reality. An address recalculation pipeline is a graphics display controller specifically designed for use with head mounted virtual reality systems, it performs orientation viewport mapping after rendering which means the users head orientation does not need to be known accurately until less than a microsecond before the first pixel of an update frame is actually sent to the head mounted display device. As a result the user perceived latency to head rotations is minimal.Using such a controller with image composition it is possible to render different objects within the world at different rate, thus it is possible to concentrate the available rendering power on the sections of the scene that change the most. The concentration of rendering power is known as priority rendering. Reductions of one order of magnitude in the number of objects rendered for an entire scene have been observed when using priority rendering. When non interactive background scenes which are rendered with a high quality rendering algorithm such as ray tracing are added to the world, highly realistic virtual worlds are possible with little or no latency.

Adaptive Shadow Testing for Ray Tracing

Abstract: We present a simple technique for improving the efficiency of ray tracing in scenes with many light sources. The sources are sorted according to their potential contribution, and only those sources whose shadows are above a specified threshold are tested. The remainder are added into the result in proportion to a statistical estimate of their visibility. The algorithm requires very littie storage, and produces no visible artifacts.

3-D network ray tracing

Abstract: SUMMARY An efficient algorithm of the network shortest path calculation of rays and traveltimes of the first arrivals is described. The traveltime error of such computations is estimated. The rough estimate of the relative traveltime error is evaluated locally at all network nodes prior to network ray tracing, and is minimized by means of a proper choice of the sizes of forward stars. In this way, the structure of the network is adjusted for a particular model and for a particular computer memory. After network ray tracing, the error estimate is refined and the absolute error bounds of the calculated traveltimes are evaluated. The method and its accuracy are demonstrated on numerical examples.

Volumetric ray tracing

Abstract: This paper presents an eficient ray tracing method for scenes containing volumetric as well as geometric data. A global illumination equation is developed for this method, which is able to capture in a single image both realistic eaects and practical volume rendering. In this method, ray-object intersection calculations result in standard intersection points, as well as intersection segments. For accuracy and eflciency, all objects along a ray are sorted according to distance and intersection classification before any intersection calculations are pelformed. The intersection results are then passed to a shaden which evaluates the intensity equation defined by the illumination model to determine the final pixel value.

Introduction To Geometrical Optics

Abstract: Light Reflection at Plane Mirrors Refraction of Light Refraction by Planes, Plates and Prisms Paraxial Refraction at Planes, Plates and Prisms Refraction and Reflection at Spherical Surfaces Thin Lenses Rotationally Symmetrical Systems Astigmatic Lenses Thick Lens Systems Stops, Pupils and Ports Numerical Aperture, f-Number and Resolution Magnifiers and Microscopes Telescopes Cameras and Projectors Ophthalmic Instruments Dispersion and Chromatic Aberration Trigonometric Ray Tracing Monochromatic Aberrations.

Ray tracing method and apparatus for projecting rays through an object represented by a set of infinite surfaces

Abstract: Each object in a 3-dimensional image to be displayed may be represented by a set of infinite surfaces. Each elementary area of a screen on which the image is to be displayed has a ray projected through it onto the 3-dimensional image. The location of the intersection of the projected ray with each surface is then determined and from these locations it is determined whether any intersected surface is visible at that elementary area. The elementary area is then shaded for display in dependence on the result of the determination.

Three dimensional view using ray tracing through voxels subdivided numerically using object based parameters

Abstract: A picture generating apparatus using ray tracing has means for inputting data of objects from a data base for storing data of objects composing a virtual three dimensional space, means for registering the data of the virtual three dimensional space divided into a plurality of voxels represented by data in a voxel table, means for determining a voxel subdivision number on the basis of representative parameters expressing geometrical information on said objects composing the three dimensional space, such as the object average size, and means for generating pictures by applying a ray tracing method to the divided voxels and displaying the generated pictures.

Gradient Calculation of the Traveltime Cost Function Without Ray Tracing

Abstract: Gradient based traveltime tomography algorithms require the computation of the gradient of the traveltime misfit cost function many times. This calculation is customarily done by ray tracing, the path length of the rays being closely related to the gradient. We propose in this work an alternative method to compute the gradient of the traveltime cost function without ray tracing. We use upwind finite difference schemes to compute the traveltime field by solving the eikonal equation. Then by adjoint state techniques we derive a closed-form expression of the gradient of the traveltime cost function. This approach allows an accurate computation of the gradient as well as the freedom to change the norm on the model space.

Computer generated copper plates

Abstract: Making computer generated copper plates with image generation algorithms is presented. The method uses a kind of volume texturing in connection with image processing algorithms, and is suitable for implementation in a ray tracing algorithm. Experience shows that this method is especially interesting for illustrations in books and for generating icons on user interfaces.

Ray tracing prediction of indoor radio propagation

Abstract: Indoor wireless systems will be used in a large variety of office, factory and residential environments. Thus, adequate guidelines for radio port placement are needed to ensure satisfactory performance at the lowest cost. These guidelines must be derived from a large body of site-specific propagation data. However, collecting a statistically significant database through measurements is a daunting task. Alternatively, this database can be generated by using propagation models, validated by measurements. Several models exist for the statistical characterization of microwave propagation within buildings, However, statistical models do not provide site-specific information. We propose a hybrid model in which ray tracing is used to predict, at any given location, the local mean of the received power and the delay profile. Variations about the mean values can then be captured via a statistical description matched to the local environment. We describe an efficient 3-D ray tracing algorithm which accounts for all (transmitted as well as reflected) rays reaching the receiver location after an arbitrary number of reflections. We include the effects of the angle of incidence, the material dielectric constant and the antenna patterns. The predicted values for the local means of the received power are then compared against measurements to establish the accuracy of this approach.

Ray tracing models for indoor environments and their computational complexity

Abstract: For indoor environments ray tracing models are frequently used to predict the impulse response of the radio channel. This contribution discusses ray tracing methods known from literature by considering the computational complexity. A new ray tracing method, based on the variation of a ray direction at the transmitter location is proposed and compared to the known methods.

Fast surface rendering from raster data by voxel traversal using chessboard distance

Abstract: The increasing distinguishing capability of tomographic and other 3D scanners as well as the new voxelization algorithms place new demands on visualization techniques aimed at interactivity and rendition quality. Among others, triangulation on a subvoxel level based on the marching cube algorithm has gained popularity in recent years. However without graphics hardware support, rendering many small triangles could be awkward. We present a surface rendering approach based on ray tracing of segmented volumetric data. We show that if a proper interpolation scheme and voxel traversal algorithm are used, high quality images can be obtained within an acceptable time and without hardware support. >

Computability and complexity of ray tracing

Abstract: The ray-tracing problem is, given an optical system and the position and direction of an initial light ray, to decide if the light ray reaches some given final position. For many years ray tracing has been used for designing and analyzing optical systems. Ray tracing is now used extensively in computer graphics to render scenes with complex curved objects under global illumination. We show that ray-tracing problems in some three-dimensional simple optical systems (purely geometrical optics) are undecidable. These systems may consist of either reflective objects that are represented by rational quadratic equations, or refractive objects that are represented by rational linear equations. Some problems in more restricted models are shown to be PSPACE-hard or sometimes in PSPACE.

Visual simulation of lightning

Abstract: A method for rendering lightning using conventional raytracing techniques is discussed. The approach taken is directed at producing aesthetic images for animation, rather than providing a realistic physically based model for rendering. A particle system is used to generate the path of the lightning channel, and subsequently to animate the lightning. A technique, using implicit surfaces, is introduced for illuminating objects struck by lightning.

A time-domain backpropagating ray technique for source localization

Abstract: A new method is presented for source localization which is based on a ray backpropagation procedure, and which exploits both the temporal and spatial characteristics of the multipath arrival structure at a receiving sensor array. The basic method consists of two steps. The first step employs a receiving sensor array to estimate the angles and relative arrival times of the various multipath trajectories which arrive at the receiver after having been emitted by the source located at an unknown range R and depth Z from the receiver. The second step utilizes a ray tracing technique to backpropagate the rays and produce an estimate of the source position by making full use of all the spatial and temporal information extracted by the array. The source signal is taken to be a narrow‐band stochastic process, which simulates a realistic situation commonly encountered in the ocean acoustic environment. Some key advantages of the approach are (1) localization ambiguity is minimized by utilizing ray travel times as well as path convergence; (2) the approach does not require full‐wave matched‐field processing; (3) ray backpropagation is numerically very efficient; (4) phase ambiguity is eliminated by employing the group delay of arriving wave packets; (5) ray chaos can be avoided simply by excluding chaotic rays from the backpropagation algorithm.

Classification of Ray‐Generators in Uniform Subdivisions and Octrees for Ray Tracing

Abstract: Spatial subdivisions cause an enormous acceleration of ray tracing due to the reduction of ray-object intersections. For this purpose it is necessary to generate the sequence of ray-cells (all cells met consecutively by a given ray). A method generating this sequence will be called a ray-generator. First this paper analyses the common properties of ray-generators in order to establish a classification. Then some well-known ray- generators are described and classified, as well as some new ones. In the sequel nine different ray-generators are implemented in one single program allowing direct comparisons with the same scene. Finally, global time measurements for two scenes are given, as well as time measurements for random rays enabling the calculation of mean values for the time of initialization and determination of ray-cells.

Height distributional distance transform methods for height field ray tracing

Abstract: Height distributional distance transform (HDDT) methods are introduced as a new class of methods for height field ray tracing. HDDT methods utilize results of height field preprocessing. The preprocessing involves computing a height field transform representing an array of cone-like volumes of empty space above the height field surface that are as wide as possible. There is one cone-like volume balanced on its apex centered above each height field cell. Various height field transforms of this type are developed. Each is based on distance transforms of height field horizontal cross-sections. HDDT methods trace rays through empty cone-like volumes instead of through successive height field cells. The performance of HDDT methods is evaluated experimentally against existing height field ray tracing methods.

FDTD simulations of indoor propagation

Abstract: This paper presents a 2D finite difference time domain method used for indoor propagation calculations. The relationship between the 2D and the 3D problem is discussed. An interpretation of the 2D results is done. The results of a sample calculation are presented and compared to those of other papers. FDTD is compared to the ray tracing method and found to be appropriate, e.g. if many reflections are to be taken into account. >

Source Selection for the Direct Lighting Computation in Global Illumination

Abstract: Computation of the global illumination in a scene can be improved by separating the direct component of the lighting, which is received by a patch directly from light sources, from the indirect component, which is received by intermediate interreflection from other patches. The indirect component is calculated during the preprocessing and is stored as the radiosity shading at the patch. The direct component is calculated during the rendering phase by tracing shadow rays like in conventional ray tracing. The number of shadow rays can be reduced by exploiting shadow coherence, and by making a selection for the number of light sources that are taken into account for the direct lighting computation. Different criteria to select these sources are given.

Subdivision of 3D Space Based on the Graph Partitioning for Parallel Ray Tracing

Abstract: An approach for parallel ray tracing is to subdivide the 3D space into rectangular volumes and assign the object descriptions with their related computations in each volume to a different processor. The subdivision process is critical in reducing the interprocessor communication overhead, and maintaining the load balance among processors of a multicomputer. In this paper, after a brief overview of parallel ray tracing, a heuristic is proposed to subdivide the 3D space by converting the problem into a graph partitioning problem. The proposed algorithm tries to minimize the communication cost while maintaining a load balance among processors.

Ray tracing general parametric surfaces using interval arithmetic

Abstract: This paper describes an algorithm for ray tracing general parametric surfaces. After dividing the surface adaptively into small parts, a binary tree of these parts is built. For each part a bounding volume is calculated with interval arithmetic. From linear approximations and intervals for the partial derivatives it is possible to construct parallelepipds that adapt the orientation and shape of the surface parts very well and form very tight enclosures. Therefore we can develop an algorithm for rendering that is similar to that used with Bezier and B-spline surfaces, where the bounding volumes are derived from the convex hull property. The tree of enclosures (generated once in a preprocessing step) guarantees that each ray that hits the surface leads to an iteration on a very small surface part; this iteration can be robustly (and very quickly) performed in real arithmetic.

Global illumination models for volume rendering

Abstract: The increasing demand for realistic images has led to the development of several global illumination models and rendering techniques. Great effort has been taken to extend these illumination models and optimize the rendering techniques to produce more realistic images in less time. Despite this effort, most of these methods are designed for scenes consisting of geometric surface descriptions, and cannot directly render volumetric data. Volumetric data sets can be rendered using volume rendering techniques that, in order to decrease rendering times and therefore increase interactivity, typically employ only a local illumination model. The development of global illumination models and rendering techniques for volumetric data is the focus of this work. These illumination methods can be used to generate realistic images of scenes containing volumetric as well as geometric data. The volumetric global illumination methods can be employed by a visualization system in order to add intuitive cues to an image for a greater three-dimensional understanding of a scene. Also, these methods allow for amorphous effects that can not be captured using geometric illumination models, including clouds, fog, and smoke. A volumetric ray tracing method is presented that encompasses classical ray tracing while allowing for volume rendering effects. The definition of an intersection is extended to include intersection points for surface contributions to the intensity equation, and intersection segments for volumetric contributions. A method for accelerating primary and shadow rays is developed. A volumetric radiosity method is presented that encompasses classical radiosity while also including isotropic and diffuse volumetric interactions. Geometric surfaces and volumetric isosurfaces are approximated using standard surface patches, and voxels are used to approximate participating volumes. Diffuse volumetric interactions make it possible to give the appearance of shaded surfaces to scenes consisting of only volumetric data. Hierarchical techniques are applied to decrease the number of interactions required for a solution. Multipass methods are developed to increase realism by combining illumination methods. A multipass method that combines volumetric ray tracing and volumetric radiosity is presented. Also, a multipass method that extends volumetric ray tracing to account for indirect specular lighting is presented.

Numerical and Experimental Analyses of the Radiant Heat Flux Produced by Quartz Heating Systems

Abstract: A method is developed for predicting the radiant heat flux distribution produced by tungsten filament, tubular fused-quartz envelope heating systems with reflectors. The method is an application of Monte Carlo simulation, which takes the form of a random walk or ray tracing scheme. The method is applied to four systems of increasing complexity, including a single lamp without a reflector, a single lamp with a flat reflector, a single lamp with a parabolic reflector, and up to six lamps in a six-lamp contoured-reflector heating unit. The application of the Monte Carlo method to the simulation of the thermal radiation generated by these systems is discussed. The procedures for numerical implementation are also presented. Experiments were conducted to study thesebreak quartz heating systems and to acquire measurements of the corresponding empirical heat flux distributions for correlation with analysis. The experiments were conducted such that several complicating factors could be isolated and studied sequentially. Comparisons of the experimental results with analysis are presented and discussed. Good agreement between the experimental and simulated results was obtained in all cases. This study shows that this method can be used to analyze very complicated quartz heating systems and can account for factors such as spectral properties, specular reflection from curved surfaces, source enhancement due to reflectors and/or adjacent sources, and interaction with a participating medium in a straightforward manner.

A new approach to indoor propagation prediction

Abstract: A new approach to indoor propagation prediction which is based on the Rayleigh-Gans approximation is proposed. The approach has been motivated by the observation that the indoor environment is different from the outdoor environment in that many of the structures within buildings are approximately the size of a wavelength making propagation prediction based on high frequency techniques not strictly applicable. In the paper details of the Rayleigh-Gans approximation are provided. Actual indoor propagation measurements are also provided to allow preliminary discussions on the accuracy of the Rayleigh-Gans approximation to be given. Comparisons with simulations of empirical and ray tracing models are also provided. The results indicate that further development would be worthwhile. >

Load balancing of parallel volume rendering with scattered decomposition

Abstract: A scheme for the visualization of large data volumes using volume rendering on a distributed memory MIMD system is described. The data to be rendered is decomposed into subvolumes to reside in the local memories of the system's nodes. A partial image of the local data is generated at each node by ray tracing, and is then composited with partial images on other nodes in the correct order to generate the complete Image. Subvolumes whose voxels are classified as being mapped to zero opacity are not rendered, giving rise to an imbalance of work amongst nodes. Scattered decomposition is used for load balancing, which on one hand: creates additional overheads in compositing and communication, but on the other, provides an improvement in throughput that is dependent on the characteristics of the data. Experimental results for a typical data set rendered on a 1024-node Fujitsu AP1000 are reported. >