Raytracing

Protectional eyewear has to fulfill both mechanical and optical stress tests. To pass those optical tests the surfaces of safety spectacles have to be optimized to minimize optical aberrations. Material and Methods: Starting with the surface data of three measured safety spectacles, a theoretical spectacle model (four spherical surfaces) is recalculated first and then optimized while keeping the front surface unchanged. Next to spherical power, astigmatic power and prism imbalance we used the wavefront error (five different viewing directions) to simulate the optical performance and to optimize the safety spectacle geometries. Results: All surfaces were spherical (maximum global deviation 'peak-to-valley' between the measured surface and the best-fit sphere: 0.132 mm). Except the spherical power of the model Axcont (−0.07 m −1 ) all simulated optical performance before optimization was better than the limits defined by standards. The optimization reduced the wavefront error by 1% to 0.150 (Windor/Infield), by 63% to 0.194 (Axcont/Bolle) and by 55% to 0.199 (2720/3 M) without dropping below the measured thickness. Conclusion: The simulated optical performance of spectacle designs could be improved when using a smart optimization. A good optical design counteracts degradation by parameter variation throughout the manufacturing process. Schlussfolgerung: Durch eine geschickte Optimierung kann die theoretische Abbildungsqualität von reellen Schutzbrillendesigns zum Teil verbessert werden. Ein gutes optisches Design wirkt Einflüssen durch Prozessparameterschwankungen in der Produktion entgegen.

امروزه صنعت پویانمایی سازی یکی از پرطرفدارترین و پر درامد ترین صنعتها محسوب میشود؛ که بخش
بزرگی از اوقات فراغت همه مردم جهان را پرکرده، چه بر روی کامپیوترهای شخصی، چه بر روی کنسولهای
بازی و حتی موبایلها که همجا به همراه داریم. ازاینرو فعالیتهای زیادی در این زمینه صورت میگیرد تا
بازیهای سرگرمکننده و متنوع را ارائه دهند. یکی از تکنیکهایی که تحول بزرگی در این صنعت ایجاد
کرده، تکنیک ردیابی پرتو در بحث تولید تصاویر گرافیکی میباشد. در سالهای گذشته تحقیقات زیادی
مبنی بر بهبود این تکنیک و کاهش زمان پردازش آن صورت گرفته. دغدغه اصلی این تکنیک زمان پردازش
آن نیز میباشد. در تلاشهای صورت گرفته تا جایی توانستهاند این زمان را کاهش دهند، اما باز نتوانستهاند
از حداکثر توان سختافزار برای کاهش این زمان استفاده کنند.در این مقاله به برسی روشهای توزیعشده و
تکی این روشها می پردازیم.

The aim of this thesis is to investigate the applicability of a novel image synthesis technique based on Monte Carlo particle transport to daylight simulation. Many materials used in daylight simulation are specifically designed to redirect light, and as such give rise to complex effects such as caustics. The photon map technique was chosen for its efficent handling of these effects. To assess its ability to produce physically correct results which can be applied to lighting simulation, a validation was carried out based on analytical case studies and on simple experimental setups. As prerequisite to validation, the photon map´s inherent bias/noise tradeoff is investigated. This tradeoff depends on the density estimate bandwidth used in the reconstruction of the illumination. The error analysis leads to the development of a bias compensating operator which adapts the bandwidth according to the estimated bias in the reconstructed illumination.

Obscurances is a powerful technique that approximates indirect global illumination in a much faster way than classic methods as radiosity or path tracing. In this method, the local environment of a point or a patch is sampled to estimate the amount of occlusion that surrounds it. Fine effects as color reflection can be added and visually pleasant rendering of corners and soft shadows are easily computed. Combined with ray tracing techniques, nondiffuse and specular effects can be added to the surfaces, obtaining thus beautiful and realistic rendered images. Since direct and indirect illumination are decoupled, obscurances are very useful to render animation frames for moving light sources, as they have to be computed only for the first frame and then reused. Ambient light intensity can also be decoupled from obscurances and estimated for every frame, resulting in beautiful colorchanging effects. Light animation help in light design and to convey shape and features of the objects in the scene.

Daylighting in tropical and sub-tropical climates presents a unique challenge that is generally not well understood by designers. In a sub-tropical region such as Brisbane, Australia the majority of the year comprises of sunny clear skies with few overcast days and as a consequence windows can easily become sources of overheating and glare. The main strategy in dealing with this issue is extensive shading on windows. However, this in turn prevents daylight penetration into buildings often causing an interior to appear gloomy and dark even though there is more than sufficient daylight available. As a result electric lighting is the main source of light, even during the day.

A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) sol-ver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the so-called ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric source. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with results of a fully integrated, but expensive 3-D optical and thermal model. It is shown that the less expensive model provides similar results and hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to max-imise the performance of linear CSP reflector layout and receiver configurations.

Photorealistic rendering is very often used area in computer graphics. It is used to display human body in medicine, buildings in architecture and also in other areas of our life. For photorealistic rendering are very important powerful computer, than it is relative difficult on computing. To render a 3D object in computer graphics a high efficient computer is needed, which enable user to work with graphic information on higher level. In some cases of data visualization rendering can slow-down the whole proccess of computing. One possibility how to solve this problem is to apply photorealistic rendering on distributed systems. Designed system is outgoing from static assigning and sharing of scene based on areas, so that the time needed for rendering doesn’t affect the whole time. Through this architecture rendering should be more effective according to time in distributed systems.

In the present paper we solve the complex problem posed by the complex motion described by the combination of translation and rotation that can be seen when observing the wheels of a vehicle passing by.. Our paper is divided in two main parts, in the first part, we will derive the relativistic equations for rolling motion without slipping and we will make some connections with the physical requirements of a relativistic raytracing algorithm. In the second part, we will review the foundations of classical raytracing algorithms and we will introduce the additional features for operation at relativistic speeds.

Uno de los métodos de representación de objetos orgánicos en 3D son los llamados blobs. Un blob es una isosuperficie definida por una expresión de potencial de campo finito. Contando con dicha expresión hemos de obtener la representación del cuerpo de la forma más adecuada. Para la representación de cuerpos en 3D suelen usarse técnicas de poligonalización, que consisten en una obtención del modelo de fronteras de la forma. Existen numerosos algoritmos que resuelven dicho problema para el caso de los blobs, casi todos basados en el padre de todos ellos: Marching Cubes. Nuestro objetivo es el estudio de dicho algoritmo para la obtención de un postproceso que nos proporcione unos resultados más correctos, sin un excesivo incremento de su complejidad computacional. Finalmente generalizaremos el postproceso para que pueda aplicarse a una malla poligonal obtenida a partir de cualquier algoritmo de poligonalización de blobs.

With the growth of high data rate speed cellular communication systems (UMTS, GSM, WiFi, Bluetooth…), prediction of the electromagnetic propagation becomes a strategic stake and an active subject of research. To give fast realistic predictions of the field strength and delay spread in wireless mobile communication networks, SILICOM developed the SLC software (note), based on parallel 3D raytracing combined with GO/UTD theory [1]. This paper describes our solution and shows its application to WiFi hotspot study.

The investigation of space debris involves the characterization of orbital objects, which includes the collection of information like orbit, body shape and attitude. Current studies are mainly concerned with methods for precise orbit determination. However, future removal missions will need additional information of the objects state – in particular the attitude. For this purpose, researchers of the Institute of Technical Physics at the German Aerospace Center (DLR) in Stuttgart, Germany started a new research campaign to investigate light curves of debris objects.

In this paper, we present a physical validation of global illumination algorithms based on measurements from a simple experimental setup. The validation methodology emphasizes tractability and error minimization. To this end, we discuss issues such as the acquisition and accurate simulation of material bidirectional reflection distribution functions (BRDFs) and the light source distribution, as well as error analysis. In addition, we present a nearest-neighbor resampling technique for BRDFs and a simple method for extracting the light source distribution from digitized high dynamic range (HDR) images. Finally, we compare the measurements to a forward and backward raytracing solution (photon map and RADIANCE, respectively) in a set of case studies.

Photon mapping is an efficient method for producing high-quality, photorealistic images with full global illumination. In this paper we present a more accurate and efficient approach to final gathering using the photon map based upon hierarchical evaluation of the photons over each surface. We use the footprint of each gather ray to calculate the irradiance estimate area rather than deriving it from the local photon density. We then describe an efficient method for computing the irradiance from the photon map given an arbitrary estimate area. Finally, we demonstrate how the technique may be used to reduce variance and increase efficiency when sampling diffuse and glossy-specular BRDFs.

A raytracing code for zone plates incorporated in the BESSY raytracing program RAY is described. This option allows one to calculate intensity distributions in a focal plane of circular or linear zone plates considering diffraction limited resolution. Zone plate material properties are also taking into account using optical constants data tables. The complete code is available as PC-Windows version.

The presentation of a recent addition to the suite of popular global illumination rendering methods is the focus of this thesis. The photon map comprises a particle transport simulation with a density estimate characterized by independency of the scene geometry and the ability to efficiently model diffuse global illumination and caustics. Its embedding in existing ray tracing environments is straightforward; an implementation of the photon map and its integration in the Minimal Rendering Toolkit (MRT) is described in detail.

Observations (e.g. Phillips, Heckman et al., Martin) have revealed cold gas with large velocity dispersions (≈300 km s −1) within the hot outflows of ultraluminous infrared galaxies (ULIRGs). This gas may trace its origin to the Rayleigh–Taylor (RT) fragmentation of a super-bubble or may arise on smaller scales. We model a ULIRG outflow at two scales to recreate this gas in three-dimensional hydrodynamic simulations using FLASH. Although resolution is limited, these models successfully produce cold gas in outflows with large velocity dispersions. Our small-scale models produce this cold gas through RT fragmentation of the super-bubble wall, but the large-scale models produce the cold gas after hot bubbles fragment the disc's gas into cold clouds which are then accelerated by thermal pressure, and supplemented by cooling within the outflow. We produce simple mock spectra to compare these simulations to observed absorption spectra and find line-widths of ≈250 km s −1 , agreeing with the lower end of observations.

This work presents a parallel algorithm to produce high-quality shaded pictures directly from Constructive Solid Geometry (CSG) in early real time. The algorithm performs a pixel parallelization of the Ray Casting tecnique of CSG models. L'articolo propone un nuovo approccio al problema della parallelizzazione dell'algoritmo di Ray Casting di modelli CSG su architettura SIMD (Connection Machine) . Dopo una breve descrizione del problema affrontato viene presentato l'algoritmo implementato ed irisultati ottenuti. Keywords : Parallel Computing, Computer Graphics, Geometric Modeling, Solid Modeling, CSG Evaluation, RayTracing, Image Synthesis. 1. Introduction The techniques to visualize geometric models depend from the scheme of representation used to describe the model. The main problem is the high computational time. Da alcuni anni nella progettazione assistita dal calcolatore (CAD) e' cresciuto l'interesse per i sistemi in grado di manipolare sofisticati mod...

The media industry is demanding increasing fidelity for their rendered images. Despite the advent of modern GPUs, the computational requirements of physically based global illumination algorithms are such that it is still not possible to render high-fidelity images in real time. The time constraints of commercial rendering are such that the user would like to have an idea as to just how long it will take to render an animated sequence, prior the actual rendering. This information is necessary to determine whether the desired quality is achievable in the time available or indeed if it is possible to afford to carry out the work on a render farm for example. This paper presents a comparison of different pixel profiling strategies which may be used to predict the overall rendering cost of a high fidelity global illumination solution. A fast rasterised scene preview is proposed which provides a more accurate positioning and weighting of samples, to achieve accurate cost prediction.

We present a technique for simulating accurate physically modelled acoustics within an outdoor urban environment and a tool that presents the acoustics alongside a visually rendered counterpart. Acoustic modelling is achieved by using a mixture of simulating ray-traced specular sound wave reflections and applying radiosity to simulate diffuse reflections. Sound rendering is applied to the energy response of the acoustic modelling stage and is used to produce a number of binaural samples for playback with headphones. The visual tool which has been created unites the acoustic renderings with an accurate 3D representation of the virtual environment. As part of this tool an interpolation technique has been implemented allowing a user controlled walkthrough of the simulated environment. This produces better sound localisation effects than listening from a set number of static locations.

We describe an approach to render massive urban models. To prevent a memory transfer bottleneck, we propose to render the models from a compressed representation directly. Our solution is based on rendering crude building outlines as polygons and generating details by ray-tracing displacement maps in the fragment shader. We demonstrate how to compress a displacement map so that a decompression algorithm can selectively and quickly access individual entries in a fragment shader. Our prototype implementation shows how a massive urban model can be compressed by a factor of 85 and outperform a basic geometry-based renderer by a factor of 40 to 80 in rendering speed.

Typical outdoor sound propagation problems are governed by two principal phenomena: (i) diffraction in the vicinity of the noise source due to objects such as buildings or insulation barriers, and (ii) refraction at long distances from the source as a consequence of the effects of wind and temperature. The boundary element method (BEM) is well suited to account for the diffraction phenomena in the near field, while the raytracing method based on geometrical acoustics is more effective to deal with the refraction phenomena.

This paper presents a fast and scalable parallel algorithm for volume rendering and its implementation on distributed-memory parallel computers. This parallel algorithm is based on the shear-warp algorithm of Lacroute and Levoy. Coupled with optimizations that exploit coherence in the volume and image space, the shear-warp algorithm is currently acknowledged to be the fastest sequential volume rendering algorithm. We have designed a memory efficient parallel formulation of this algorithm that (1) drastically reduces communication requirements by using a novel data partitioning scheme and (2) improves multi-frame performance with an adaptive load-balancing technique. All the optimizations of the Lacroute-Levoy algorithm are preserved in the parallel formulation. The paper also provides an analytical model of performance for the parallel formulation that shows that it is possible to sustain excellent performance across a wide range of practical problem sizes and number of processors. Our implementation, running on a 128 processor TMC CM-5 distributed-memory parallel computer, renders a 256 3 voxel medical data set at 12 frames/sec.

We describe an approach to render massive urban models. To prevent a memory transfer bottleneck, we propose to render the models from a compressed representation directly. Our solution is based on rendering crude building outlines as polygons and generating details by ray-tracing displacement maps in the fragment shader. We demonstrate how to compress a displacement map so that a decompression algorithm can selectively and quickly access individual entries in a fragment shader. Our prototype implementation shows how a massive urban model can be compressed by a factor of 85 and outperform a basic geometry-based renderer by a factor of 40 to 80 in rendering speed.

Density estimation techniques such as the photon map method rely on a particle transport simulation to reconstruct indirect illumination, which is proportional to the particle density. In the photon map framework, particles are usually located using nearest-neighbour methods due to their generality. However, these methods have an inherent tradeoff between local bias and noise in the reconstructed illumination, which depends on the density estimate bandwidth. This paper presents a bias compensating operator for nearest-neighbour density estimation which adapts the bandwidth according to the estimated bias in the reconstructed illumination.

A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) solver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the socalled ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared with and validated against those obtained with the Monte Carlo ray tracer, SolTrace. The outcome of the FV ray tracing in the LFC optical domain is mapped as a non-uniform heat flux distribution in the 3-D cavity receiver domain and this distribution is included in the FV conjugate heat transfer CFD model as a volumetric source. The result of this latter model is the determination of the heat transferred to the heat transfer fluid running in the collector tubes, thereby providing an estimation of the overall thermal efficiency. To evaluate the effectiveness of the phased approach in terms of accuracy and computational cost, the novel 2-D:3-D phased approach is compared with results of a fully integrated, but expensive 3-D optical and thermal model. It is shown that the less expensive model provides similar results and hence a large cost saving. The novel approach also provides the benefit of working in one simulation environment, i.e. ANSYS Workbench, where optimisation studies can be carried out to maximise the performance of linear CSP reflector layout and receiver configurations.

A computational approach is presented, which uses the finite volume (FV) method in the Computational Fluid Dynamics (CFD) sol-ver ANSYS Fluent to conduct the ray tracing required to quantify the optical performance of a line concentration Concentrated Solar Power (CSP) receiver, as well as the conjugate heat transfer modelling required to estimate the thermal efficiency of such a receiver. A Linear Fresnel Collector (LFC) implementation is used to illustrate the approach. It is shown that the Discrete Ordinates method can provide an accurate solution to the Radiative Transfer Equation (RTE) if the shortcomings of its solution are resolved appropriately in the FV CFD solver. The shortcomings are due to false scattering and the so-called ray effect inherent in the FV solution. The approach is first evaluated for a 2-D test case involving oblique collimated radiation and then for a more complex 2-D LFC optical domain based on the FRESDEMO project. For the latter, results are compared w...

This paper describes an object-order real-time volume rendering architecture using an adaptive resampling scheme to perform resampling operations in a unified parallel-pipeline manner for both parallel and perspective projections. Unlike parallel projections, perspective projections require a variable resampling structure due to diverging perspective rays. In order to address this issue, we propose an adaptive pipelined convolution block for resampling operations using the level of resolution to keep the parallel-pipeline structure regular. We also propose to use multi-resolution datasets prepared for different levels of grid resolution to bound the convolution operations. The proposed convolution block is organized using a systolic array structure, which works well with a distributed skewed memory for conflict-free accesses of voxels. We present the results of some experiments with our software simulators of the proposed architecture and discuss about important technical issues.

Lightcuts is a scalable framework for computing realistic illumination. It handles arbitrary geometry, non-diffuse materials, and illumination from a wide variety of sources including point lights, area lights, HDR environment maps, sun/sky models, and indirect illumination. At its core is a new algorithm for accurately approximating illumination from many point lights with a strongly sublinear cost. We show how a group of lights can be cheaply approximated while bounding the maximum approximation error. A binary light tree and perceptual metric are then used to adaptively partition the lights into groups to control the error vs. cost tradeoff. We also introduce reconstruction cuts that exploit spatial coherence to accelerate the generation of anti-aliased images with complex illumination. Results are demonstrated for five complex scenes and show that lightcuts can accurately approximate hundreds of thousands of point lights using only a few hundred shadow rays. Reconstruction cuts can reduce the number of shadow rays to tens.

Annual simulation is a significant indicator of a daylight redirecting component's performance, since it accounts for seasonal variations in daylight availability as well as the system's response under such conditions. This study details the simulation of a representative redirecting component using a 3D forward raytracing technique to assess its annual daylighting performance. We streamline and largely automate this workflow with the EvalDRC tool, a Python script which implements a simulation frontend based on the Radiance photon map, coupled to a postprocessing and evaluation backend. The redirecting component selected for our case study combines retroreflection with redirection and is designed for optimal daylight availability over the entire year without the need for adjustment. The lamella profile can be mounted in a forward and reversed configuration to combine retroreflection with redirection in the lower resp. upper portions of the fenestration. We evaluate our simulations visually and numerically as high dynamic range (HDR) renderings and a spatial daylight autonomy (sDA) metric based on climate based sky distributions for Geneva, Switzerland. Our case study satisfies the sDA requirement that 55% of the workplane receives an illuminance exceeding 300 lux during 50% or more of the occupancy hours for a whole year. In addition, we propose the msDA, a detailed monthly breakdown of the sDA, for which the criteria are specifically met in the months March-September, while a minimum of 32% is predicted for December. Our results demonstrate the effectiveness of photon mapping for this application, and that the simulation accurately predicts the redirecting component's expected seasonal behaviour for multiple solar angles and sky configurations. This applies in particular to complex redirecting systems which cannot be reliably simulated with a backward raytracer at reasonable computational cost.

This paper introduces a new multipass algorithm for efficiently computing direct illumination in scenes with many lights and complex occlusion. Images are first divided into 8 Â 8 pixel blocks and for each point to be shaded within a block, a probability density function (PDF) is constructed over the lights and sampled to estimate illumination using a small number of shadow rays. Information from these samples is then aggregated at both the pixel and block level and used to optimize the PDFs for the next pass. Over multiple passes the PDFs and pixel estimates are updated until convergence. Using aggregation and feedback progressively improves the sampling and automatically exploits both visibility and spatial coherence. We also use novel extensions for efficient antialiasing. Our adaptive multipass approach computes accurate direct illumination eight times faster than prior approaches in tests on several complex scenes.

Uno de los métodos de representación de objetos orgánicos en 3D son los llamados blobs. Un blob es una isosuperficie definida por una expresión de potencial de campo finito. Contando con dicha expresión hemos de obtener la representación del cuerpo de la forma más adecuada. Para la representación de cuerpos en 3D suelen usarse técnicas de poligonalización, que consisten en una obtención del modelo de fronteras de la forma. Existen numerosos algoritmos que resuelven dicho problema para el caso de los blobs, casi todos basados en el padre de todos ellos: Marching Cubes. Nuestro objetivo es el estudio de dicho algoritmo para la obtención de un postproceso que nos proporcione unos resultados más correctos, sin un excesivo incremento de su complejidad computacional. Finalmente generalizaremos el postproceso para que pueda aplicarse a una malla poligonal obtenida a partir de cualquier algoritmo de poligonalización de blobs.

This technical report documents the development of the RADIANCE photon mapping extension and its integration into the official RADIANCE 5.0 distribution. A number of new techniques are now supported for a more efficient daylight simulation workflow, notably support for data driven material models via the bsdf modifier, and ray coefficients for climate based daylight modelling using the rcontrib tool. This document focuses primarily on the implementation details of the photon mapping software in support of this new functionality.