Traditional Ray Tracing Research Articles

Deep learning-driven optimization of real-time ray tracing for enhanced immersive virtual reality

Photorealistic rendering is essential for immersive virtual reality and real-time ray tracing is required for this, yet the necessary computational load has so far hindered its use in scenarios where a fast response and high frame rates are paramount. To overcome this challenge, we present a deep learning-based model that optimises the computational load of ray tracing through utilising convolutional neural networks (CNNs) to predict lightscene interactions. We achieve this by training CNNs from datasets with offline ray-traced images. Using this learning process, we approximate the contents of light transport simulations from scene point sampling. The use of this optimised algorithm in virtual reality scenes, thus, enables renderings of more complex scenes, with dynamic lighting, complex geometry and interactive elements under high frame rates, keeping users immersed and responsive to events. Our results show that this method achieves visual similarities to traditional ray tracing, which is photorealistic rendering, but can be performed in real-time in virtual reality. We anticipate this work leads to many potential applications of ray tracing in many scenarios in virtual reality, such as gaming, architectural rendering and training.

18‐1: A Super‐fast and Precise Moiré Pattern Simulation Algorithm for Improving Antenna‐on‐Display Moiré Effect

This study introduces a super‐fast and precise simulation algorithm capable of generating human‐visible moiré patterns, taking into account real structures with diverse patterns. The simulation of entire area of a mobile phone screen can be completed in less than 10 minutes, demonstrating a remarkable efficiency improvement of approximately 1200‐fold compared to traditional ray tracing method. The improvement comes from that we use a simplified method of calculating geometric areas instead of the first‐principles approach used in ray tracing. Based on the proposed algorithm, the moiré patterns ofAoD are optimized and the display quality is guaranteed.

Specular Path Generation and Near-Reflective Diffraction in Interactive Acoustical Simulations.

Most systems for simulating sound propagation in a virtual environment for interactive applications use ray- or path-based models of sound. With these models, the "early" (low-order) specular reflection paths play a key role in defining the "sound" of the environment. However, the wave nature of sound, and the fact that smooth objects are approximated by triangle meshes, pose challenges for creating realistic approximations of the reflection results. Existing methods which produce accurate results are too slow to be used in most interactive applications with dynamic scenes. This paper presents a method for reflections modeling called spatially sampled near-reflective diffraction (SSNRD), based on an existing approximate diffraction model, Volumetric Diffraction and Transmission (VDaT). The SSNRD model addresses the challenges mentioned above, produces results accurate to within 1-2 dB on average compared to edge diffraction, and is fast enough to generate thousands of paths in a few milliseconds in large scenes. This method encompasses scene geometry processing, path trajectory generation, spatial sampling for diffraction modeling, and a small deep neural network (DNN) to produce the final response of each path. All steps of the method are GPU-accelerated, and NVIDIA RTX real-time ray tracing hardware is used for spatial computing tasks beyond just traditional ray tracing.

A New Ray Tracing Method Based on Piecewise Conformal Transformations

We put forward a new ray tracing method for electromagnetic wave propagation based on piecewise conformal transformations. Our approach is based on our previous research, where conformal transformation was focused on giving an accurate formula for the effective Earth radius. In this article, according to the height interval of atmospheric refractive index data, we approximate the electromagnetic wave propagation path by the combination of circular arcs with different curvature radius and find the effective Earth radius of each arc using conformal transformations. Then, upon using the effective Earth radius, we transform the circular arc path into a straight path, thus simplifying the calculations needed to describe the propagation of electromagnetic waves. We compare our approach to the traditional ray tracing method for several typical atmospheric refractive index profiles and prove that our new method may achieve ray tracing with higher accuracy using fewer path points. We also consider nonuniform atmosphere and irregular terrain and compare the performance of our ray tracing scheme with that of the open-source software PETOOL, which is based on the parabolic equation method. Result proves that the new method may be effectively used for ray tracing in complex environments.

Dominant path determining method for millimeter wave propagation in indoor scenarios based on ant colony algorithm

A fast ray tracing method based on ant colony algorithm is proposed to analyze the indoor propagation characteristics of millimeter-wave more efficiently. This method uses ant colony distribution calculation and heuristic search principle to find the dominant ray path of radio wave propagation, which replaces the total ray path analysis to reduce the algorithm complexity and improve execution efficiency. Compared with the measured data results, the result of the simulation analysis of three frequency channel characteristics of 28 GHz, 32 GHz and 38 GHz in typical indoor scene shows better consistency, and the prediction error is less than 0.8 dB. The computational efficiency is improved by 378.9% compared with the traditional ray tracing method. The above-mentioned results show that the proposed method can effectively reduce the computational complexity under the premise of ensuring the prediction accuracy, and has the value of engineering application.

Ray Tracing Method of Gradient Refractive Index Medium Based on Refractive Index Step

For gradient refractive index media with large refractive index gradients, traditional ray tracing methods based on refined elements or spatial geometric steps have problems such as low tracing accuracy and efficiency. The ray tracing method based on refractive index steps proposed in this paper can effectively solve this problem. This method uses the refractive index step to replace the spatial geometric step. The starting point and the end point of each ray tracing step are on the constant refractive-index surfaces. It avoids the problem that the traditional tracing method cannot adapt to the area of sudden change in the refractive index and the area where the refractive index changes sharply. Therefore, a suitable distance can be performed in the iterative process. It can achieve high-efficiency and precise ray tracing in areas whether the refractive index changes slowly or sharply. According to the comparison of calculation examples, this method can achieve a tracing accuracy of 10−5 mm. The speed and precision of ray tracing are better than traditional methods.

Optimal calculation method of aircraft infrared physical imaging simulation

In order to meet the needs of high-precision simulation images in the development process of infrared imaging detection system, the infrared physical imaging radiation transmission model for aircraft was established, and the ray tracing method was used to realize the simulation calculation of radiance image. Aiming at the difference between the reflection characteristics of the aircraft skin and the distribution characteristics of the radiation source, an optimization method for skin radiance calculation using direct lighting multi-importance sampling was proposed. Aiming at the characteristics of strong emission ability and weak extinction ability of aircraft exhaust plume, an optimization method for exhaust plume radiance calculation using combining integration was proposed. The correctness and effectiveness of the physical imaging model and calculation optimization method were verified through simulation experiments. The relative error of the skin radiation calculation is better than 0.05%, and the relative error of the tail flame radiation calculation is better than 0.1%. Compared with the traditional ray tracing method, the calculation optimization method has a faster convergence speed and stronger adaptability. Infrared imaging simulation and radiation characteristics analysis of stealth aircraft were carried out. The simulation results show that infrared stealth technology can reduce the radiation intensity in the mid-waveband and long-waveband, and increase the reflected radiation intensity in the short-waveband.

Finite element modeling of coating thickness using heat transfer method

A new heat transfer based finite element model is proposed to simulate coating thickness in the electron-beam physical vapor deposition (EB-PVD) process. The major advantage of the proposed model is that it is much computationally efficient than the traditional ray-tracing based model by about two orders of magnitude. This is because the Gaussian distribution heating source has the same profile as the cosine relation used in the ray-tracing method. Firstly, the model simulates the temperature profile of a metal substrate heated by a heating source with a Gaussian distribution. Then using a calibrated conversion process, the temperature profile is converted to corresponding coating thickness. The model is successfully demonstrated by three validation cases, including a stationary disk, a stationary cylinder, and a rotary three-pin component. The predicted coating thicknesses in the validation cases are in good agreement with either the ray-tracing based analytical solution or experimental data. After its validation, the model is applied to a rotary turbine blade to predict its coating thickness distribution. In summary, the model is capable to simulate coating thickness in complex shaped parts.

Stage acoustics and parametric design: The development of an integrated early design tool

Traditional ray tracing software tools (e.g. Odeon, CATT-Acoustic, EASE) enable detailed analysis of stage acoustics; however, they are typically undertaken in later design stages and lack the flexibility required for early design development. This paper, which follows from a poster presentation at ISRA 2019, investigates the use of a three-dimensional modelling platform (Rhinoceros/Grasshopper) to quickly assess the influence of architectural changes on reflections that support orchestral ensemble. This approach enables immediate feedback, a more creative design process and better integration of architecture and acoustics. Early reflections have been found to be vital for effective orchestral ensemble. Therefore, the study focused on the investigation of early energy distribution on stage with ray tracing analysis using a parametric tool. This tool also considers cross-stage shielding effects from the orchestra and the directivity of instruments. The results of the tool have been compared to an existing acoustic modelling software to determine its accuracy and reliability. Additionally, the expansion of the tool with an evolutionary solver has also been explored. The development of a Rhinoceros/Grasshopper design tool has been found to be beneficial in the analysis of stage conditions and enhances the design collaboration during early design phases.

A Ray-Tracing Algorithm Based on the Computation of (Exact) Ray Paths With Bidirectional Ray-Tracing

A novel ray-tracing algorithm to cope with the phase errors due to incorrect ray path computations in ray-launching approaches is presented. The algorithm utilizes bidirectional ray-tracing to collect information about wavefronts incident on an interaction surface and yields considerable improvements in accuracy compared to conventional unidirectional ray-tracing. The points, where exact ray paths intersect with the surface, are obtained according to the Fermat principle of least time. If the interaction surface is aligned with diffraction edges, the corresponding critical points of the second kind can also be retrieved and complicated diffraction treatments by shooting diffracted rays on Keller cones can be avoided. Thus, a substantial reduction in the number of rays can be achieved. Furthermore, a typical problem encountered in traditional ray-tracing due to the reception sphere mechanism, i.e., incorrect ray contributions, can mostly be evaded. Numerical results demonstrate the capabilities of the new algorithm and its advantages against traditional techniques.

Compressive sensing approaches for the prediction of scattered electromagnetic fields.

We present a novel method based on Huygens' principle and compressive sensing to predict the electromagnetic (EM) fields in arbitrary scattering environments by making a few measurements of the field. In doing so, we assume a homogeneous medium between the scatterers, though we do not assume prior knowledge of the permittivities or the exact geometry of the scatterers. The major contribution of this work is a compressive sensing-based subspace optimization method (CS-SOM). Using this, we show that the EM fields in an indoor situation with up to four scattering objects can be reconstructed with approximately 12% error, when the number of measurements is only 55% of the number of variables used to formulate the problem. Our technique departs significantly from traditional ray tracing approaches. We use a surface integral formulation which captures wave-matter interactions exactly, leverage compressive sensing techniques so that field measurements at a few random locations suffice, and apply Huygens' principle to predict the fields at any location in space.

An adaptive rendering framework for efficient synthetic light field generation

Real-time global illumination rendering is very desirable for emerging applications such as Virtual Reality (VR) and Augmented Reality (AR). However, client devices have difficulties to support photo-realistic rendering, such as Ray-Tracing, due to insufficient computing resources. Many modern frameworks adopted Light Field rendering to support device displaying. A Light Field can be precomputed and stored in the Cloud. During runtime, the display extracts the color information from the Light Field to generate arbitrary real time viewpoints or re-focusing within a predefined area. To efficiently compute the Light Field, We have combined DIBR (Depth-Image-Based-Rendering) and traditional ray-tracing in an adaptive fashion to synthesize images. By measuring the color errors during runtime, we adaptively determine a good balance between DIBR and Ray Tracing. We study several cases and problems when combing these algorithms and came up with a more efficient solution. To further optimize the computation efficiency, we also added a multi-level design to exploit the degree of shareable pixels among images to control the computation for error reduction. In addition, we also design an efficient multi-threading scheduling to show the scalability of our approach. Experiments show that when the number of threads is small, we achieved up to 3.24X speedup in Light Field generation for relative simple scenes like Cornell Box, and about 2X speed up for complex scenes like Conference Room or Sponza. In the multi-thread environment, our proposed scheme can offer about 2X speedup over traditional ones.

GPU Acceleration and Game Engines for Wireless Channel Estimation in Millimeter Waves

In this article, the intended purpose is to show an innovative technique for estimating the MIMO channel at millimeter wave bands, candidates for mobile 5G technology, by using hardware acceleration, game engines and heuristic algorithms applied to optical ray launching techniques. To verify the performance of the ray launching tool, the normalized Power Delay Profile (PDP) was simulated. The channel was analyzed using the mean square delay error (RMS), the average value of the delay (MD) and the basic propagation loss (PL). The results obtained in computational precision and time were compared with those of a traditional ray tracing tool simulation programmed in MATLAB and with the measurements made in the 57 to 66 GHz range in a specialized laboratory. The results show that the presented technique becomes efficiently profitable from a small number of simulated events (reflections, diffractions).

A Parallel CE-LOD-FDTD Model for Instrument Landing System Signal Disturbance Analyzing

Before a new airport runway is built, the electromagnetic compatibility of the instrument landing system (ILS) must be fully taken into consideration. The electromagnetic compatibility requirements for airports are becoming more and more complex, so rather than using traditional ray-tracing (RT) simulation models, a more accurate approach such as the finite-difference time domain (FDTD) is needed. The application of FDTD to ILS signal modeling suffers from an intensively high computation burden. The computation burden is owing to: 1) the FDTD has to loop a large number of time steps and 2) for every step, a huge number of cells has to be updated. This paper solves the above-mentioned issues by twofold. First, this model allows a large Courant–Friedrich–Levy number for the FDTD to reduce the total time step. This is achieved by combining the locally one-dimension (LOD) FDTD and the complex-envelope (CE) technique. The combination of CE, LOD, and FDTD (CE-LOD-FDTD) makes the model update with larger time step and retain the same level of accuracy. Second, we propose a set of novel GPU-based acceleration algorithms to update the field in parallel for reducing the computation time. By comparing the measurement results, it is shown that the FDTD model is more accurate than the traditional RT-based method. Our GPU-based CE-LOD-FDTD model is 22 times faster than the conventional parallel FDTD model in a multicore machine.

Fast solar radiation pressure modelling with ray tracing and multiple reflections

Physics based SRP (Solar Radiation Pressure) models using ray tracing methods are powerful tools when modelling the forces on complex real world space vehicles. Currently high resolution (1 mm) ray tracing with secondary intersections is done on high performance computers at UCL (University College London). This study introduces the BVH (Bounding Volume Hierarchy) into the ray tracing approach for physics based SRP modelling and makes it possible to run high resolution analysis on personal computers. The ray tracer is both general and efficient enough to cope with the complex shape of satellites and multiple reflections (three or more, with no upper limit). In this study, the traditional ray tracing technique is introduced in the first place and then the BVH is integrated into the ray tracing. Four aspects of the ray tracer were tested for investigating the performance including runtime, accuracy, the effects of multiple reflections and the effects of pixel array resolution.Test results in runtime on GPS IIR and Galileo IOV (In Orbit Validation) satellites show that the BVH can make the force model computation 30–50 times faster. The ray tracer has an absolute accuracy of several nanonewtons by comparing the test results for spheres and planes with the analytical computations. The multiple reflection effects are investigated both in the intersection number and acceleration on GPS IIR, Galileo IOV and Sentinel-1 spacecraft. Considering the number of intersections, the 3rd reflection can capture 99.12%,99.14%, and 91.34% of the total reflections for GPS IIR, Galileo IOV satellite bus and the Sentinel-1 spacecraft respectively. In terms of the multiple reflection effects on the acceleration, the secondary reflection effect for Galileo IOV satellite and Sentinel-1 can reach 0.2 nm/s2 and 0.4 nm/s2 respectively. The error percentage in the accelerations magnitude results show that the 3rd reflection should be considered in order to make it less than 0.035%. The pixel array resolution tests show that the dimensions of the components have to be considered when choosing the spacing of the pixel in order not to miss some components of the satellite in ray tracing. This paper presents the first systematic and quantitative study of the secondary and higher order intersection effects. It shows conclusively the effect is non-negligible for certain classes of misson.

A comparison on initial-value ray tracing and fast marching eikonal solver for VTI traveltime computing

The Earth's subsurface is an anisotropic medium where the velocity of seismic waves alters in different propagation angles. Omitting anisotropy in seismic imaging not only brings mis-positioning of migrated dipping events but also fails to retain dipping energy during dip-moveout. To account for the efficacy of seismic anisotropy in imaging, an anisotropic wave equation must be engaged. Seismic traveltime computing is fundamental of both Kirchhoff migration and tomography algorithms. Two main categories of traveltime computing involve traditional ray tracing methods and finite difference eikonal solvers. In this study, we present two techniques of initial-value ray tracing and fast marching eikonal solver in isotropic and vertical transverse isotropy (VTI) media, and a comparison between results is demonstrated for more evaluation. Although the ray tracing approach is able to compute multiple arrivals with great precision, the eikonal solver is faster and more robust for traveltime computation. Since the ray tracing result is not a deterministic solution and it depends on the initial circumstance, employing the eikonal solver method are more preferred and suggested.

Signature simulation of infrared target by tracing multiple areal sources

The traditional ray tracing approach for infrared (IR) target simulation takes into account the radiance emitted from the target in the scene, resulting in an incomplete IR signature of a target. We present a practical method to enable the identification of the signature by considering radiation exchanges among all sources in the scene. Any source would contribute radiance to a target of interest. Therefore, the radiance of a target received by an IR imager includes self-emission and reflectance, where the reflectance is contributed due to radiation exchanges from other sources. Field experiments were performed to demonstrate our proposed method by comparisons of radiance profiles between our simulated images and the real scene images. It shows that our simulated images achieve a better match with the data than those generated by the traditional approach.

New challenges in ray tracing simulations of X-ray optics

The construction of new synchrotron sources and the refurbishment and upgrade of existing ones has boosted in the last years the interest in X-ray optics simulations for beamline design and optimization. In the last years we conducted a full renewal of the well established SHADOW ray tracing code, ending with a modular version SHADOW3 interfaced to multiple programming languages (C, C++, IDL, Python). Some of the new features of SHADOW3 are presented. From the physics point of view, SHADOW3 has been upgraded for dealing with lens systems. X-ray partial coherence applications demand an extension of traditional ray tracing methods into a hybrid ray-tracing wave-optics approach. The software development is essential for fulfilling the requests of the ESRF Upgrade Programme, and some examples of calculations are also presented.

Implementation of Reflection on Curved Surfaces and Physical Optics in Ray Tracing for Tunnel Propagation

For the modeling of multipath propagation in every wireless systems, the ray tracing method has been widely studied. However, large errors may result due to the approximation of geometrical optics in curved surfaces. This paper therefore focused on the curved surfaces and edges, which are difficult to handle in ray tracing. Examples of curved surfaces can be found in arched cross-section tunnels which are common in highway networks of mountainous areas. The traditional ray tracing method of dividing the curved surface into smaller flat plates is not so accurate as the size of smaller plates may not satisfy the geometrical optics assumption, and the reflection point which satisfies Fermat's principle may not exist. In this work, a new ray tracing method is proposed with 2 contributions. The first one is the implementation of the reflection coefficient for curved surfaces in ray tracing. The second is applying the physical optics method on the caustics region. To evaluate these methods, path gain simulation results for an arched cross-section model are compared with measurements made inside an arched tunnel. To further improve the simulation results, the effect of rough surface is introduced, and the results are again compared with measurement.

Graphical processing units and scientific applications

This special issue of the International Journal of High Performance Computing Applications collects extended versions of the best three papers presented at the International Workshop on GPUs and Scientific Applications (GPUScA 2010) held in Vienna in September 2010, in conjunction with PACT 2010 – the Annual International Conference on Parallel Architectures and Compilation Techniques. GPUs are cost-effective platforms for computationally intensive applications, providing tremendous peak performance. However, it is a major challenge to deliver the intrinsic performance of such architectures to end applications. The workshop addressed programming approaches and key techniques to leverage the computing power of GPUs. The paper Fast GPU perspective grid construction and triangle tracing for exhaustive ray tracing of highly coherent rays from Lancelot Perrotte and Guillaume Saupin, CEA-LIST (France), addresses the problem of computing, storing and sorting, at an interactive rate, all of the intersections between millions of triangles (a 3D scene) and millions of rays starting from the same point. This paper focuses on the fast GPU construction of a grid in projective space referencing the triangles of a 3D scene. It introduces a fast GPU algorithm which is used to build a grid of the rays constituting the scene, in the same projective space. This ray-based grid is computed during the initialization of the scene, which allows higher performance to be achieved, and the construction of a triangle-based grid in distinct passes for very large scenes, without having to manage memory transfers between CPUs and GPUs. This algorithm works the same way for both static and dynamic scenes, allowing interactive processing of complex and dynamic scenes to be achieved. These optimizations are used to speed up the geometrical computations used in the nuclear field to evaluate the impact of radiative sources on an operator. These geometrical computations are similar to those of traditional ray tracing, except that only highly coherent rays are thrown. The paper A framework for GPU accelerated deformable object modeling from Aria Shahingohar and Roy Eagleson, University of Western Ontario (Canada), describes a framework that uses multi-core CPUs and GPUs found in personal computers to accelerate the computations needed for a class of deformable object modeling algorithms. In recent years there has been growing interest in using deformable objects in computer applications such as animation, video games, garment CAD, and surgical simulation. Deformable object modeling is quite computationally expensive. However, since most of the related calculations can be parallelized, the authors have developed a framework that utilizes NVIDIA’s CUDA technology to accelerate a set of deformable object modeling algorithms by transferring their core computations to the GPU. Their results show that frame rates can be improved more than 20 times using GPU compared with using a multi-core CPU. In addition, they have developed a method called ‘Local Shape Matching’ which is an extension of the ‘Shape Matching’ method. Using this new method they have achieved fast and robust simulations. The paper Combining lattice Boltzmann and discrete element methods on a graphics processor from Andreas Monitzer, University of Applied Sciences Technikum Wien (Austria), deals with an original GPU-based implementation of the lattice Boltzmann method. It allows the simulation of fluids using basic arithmetic operations with a linear complexity, as is demonstrated in the paper. Additionally, the discrete element method can also be adapted to the new model. After outlining the method themselves and the integration of these two into a single simulation, this article shows a way to implement it on graphics cards using the CUDA platform.