Parallel Ray Tracing Research Articles

PyC[formula omitted]Ray: A flexible and GPU-accelerated radiative transfer framework for simulating the cosmic epoch of reionization

Detailed modeling of the evolution of neutral hydrogen in the intergalactic medium during the Epoch of Reionization, 5≤z≤20, is critical in interpreting the cosmological signals from current and upcoming 21-cm experiments such as the Low-Frequency Array (LOFAR) and the Square Kilometre Array (SKA). Numerical radiative transfer codes provide the most physically accurate models of the reionization process. However, they are computationally expensive as they must encompass enormous cosmological volumes while accurately capturing astrophysical processes occurring at small scales (≲Mpc). Here, we present pyC2Ray, an updated version of the massively parallel ray-tracing and chemistry code, C2-Ray, which has been extensively employed in reionization simulations. The most time-consuming part of the code is calculating the hydrogen column density along the path of the ionizing photons. Here, we present the Accelerated Short-characteristics Octahedral ray-tracing (ASORA) method, a ray-tracing algorithm specifically designed to run on graphical processing units (GPUs). We include a modern Python interface, allowing easy and customized use of the code without compromising computational efficiency. We test pyC2Ray on a series of standard ray-tracing tests and a complete cosmological simulation with volume size (349Mpc)3, mesh size of 2503 and approximately 106 sources. Compared to the original code, pyC2Ray achieves the same results with negligible fractional differences, ∼10−5, and a speedup factor of two orders of magnitude. Benchmark analysis shows that ASORA takes a few nanoseconds per source per voxel and scales linearly for an increasing number of sources and voxels within the ray-tracing radii.

Fast annual daylighting simulation and high dynamic range image processing using NumPy

Annual daylighting and point-in-time glare calculations depend on manipulating large matrices representing annual light levels and image pixels, respectively. Advances in computation speed have allowed modern green building standards like LEED, WELL, and EN 17037 to require annual daylighting calculations at a fine resolution across a building’s floorplate. As parallel ray tracing speeds become faster and cameras increase in resolution, matrix manipulation itself has emerged as a bottleneck to delivering fast simulation results. This paper describes a how vectorized computation methods can be applied to annual daylighting simulation and high dynamic range (HDR) image processing. Vectorization allows a computer to perform simple operations on large amounts of data simultaneously. We use the NumPy library in Python to vectorize multiple steps in the calculation of spatial daylight autonomy and annual renderings for glare as example climate-based daylighting metrics, achieving a speedup of two orders of magnitude. We also show that NumPy can manipulate large HDR images with speedups for individual operations up to six orders of magnitude.

Application of layer view factor method in high temperature thermal storage packed bed

This study provides a comprehensive evaluation of radiation effects on the thermal behavior of a packed bed using a discrete model for heat transfers integrating a novel method called Layer View Factor for view factors estimation, which significantly decreases computational time by less than 9000 times compared to the parallel ray tracing method. The model is validated and strongly aligned with experimental data at 823K, with a maximum mean bias and root mean square errors of ±4.5K and 10K, respectively. Analyses of temperature profiles and thermocline lengths for charging, discharging, and stand-by processes at a charge temperature of 1473K were performed, finding a thermal flattening effect with radiation, leading to lower peak temperatures and quicker thermocline length evolutions. Notably, the stand-by process exhibited the largest impact, with a maximum temperature difference of up to 100K compared to the non-radiation case. Moreover, analysis of the temperature and energy of discharge found that the maximum discharge temperature drops below 90% of the charge temperature when radiation is included. Finally, efficiency analysis of the processes showed differences of up to 2% between having or not the radiation effect, aiming its role as a redistribution mechanism in the packed bed’s temperature.

Parallel ray tracing through freeform lenses with NURBS surfaces

We implement Monte Carlo-based parallel ray tracing to achieve quick irradiance evaluation for freeform lenses with non-uniform rational B-splines (NURBS) surfaces. We employ the inverse transform sampling method to sample rays uniformly from the Lambertian light source and adopt the analytical form of the B-spline basis function to achieve fast surface interpolation. When performing parallel calculations for the intersections between the rays and the NURBS surfaces, we propose a parameter transformation method to avoid the parameters escaping from the defined range in the iteration process. Simulation results of two complex picture-generating freeform lenses show that our method is fast and effective.

A learning experience toward the understanding of abstraction-level interactions in parallel applications

In the curriculum of a Computer Engineering program, concepts like parallelism, concurrency, consistency, or atomicity are usually addressed in separate courses due to their thoroughness and extension. Isolating such concepts in courses helps students not only to focus on specific aspects, but also to experience the reality of working with modern computer systems, where those concepts are often detached in different abstraction levels. However, due to such an isolation, it exists a risk of inducing to the students an absence of interactions between these concepts, and, by extension, between the different abstraction levels of a system.This paper proposes a learning experience showcasing the interactions between abstraction levels addressed in laboratory sessions of different courses. The driving example is a parallel ray tracer. In the different courses, students implement and assemble components of this application from the algorithmic level of the tracer to the assembly instructions required to guarantee atomicity. Each lab focuses on a single abstraction level, but shows students the interactions with the rest of the levels. Technical results and student learning outcomes through the analysis of surveys validate the proposed experience and confirm the students learning improvement with a more integrated view of the system.

A LiDAR System Simulator Using Parallel Raytracing and Validated by Comparison with a Real Sensor

The advances in 3D imaging and Computer Vision are allowing for a massive acquisition of data, especially in the form of point clouds. However, scanning with these sensors can be costly and time consuming, reducing the efficiency of certain procedures, like deep learning dataset generation and forest canopy calculation. One trending solution is the creation of 3D imaging sensor simulators. This paper presents a simulator for light detection and ranging (LiDAR) systems with a parallel raytracing approach and a flexible scene creator. Finally, the simulator sensor is validated with a real LiDAR data.

Ray tracing collision detection based on GPU pipeline reorganization

This paper proposes a parallel collision detection algorithm based on ray tracing to improve GPU performance. The algorithm uses parallel ray tracing pipeline technology to improve the performance of the graphics processing unit (GPU). When the GPU combines multiple ray tracing, it will cause the work group threads to diverge, resulting in too many idle threads, which will reduce the performance of the system. In order to avoid thread divergence, a new collision detection technology for the detailed detection stage of ray tracing using a pipeline structure is proposed. By optimizing the addition of buffers, the ray tracing is divided into three stages, and the pipeline is designed to integrate multiple rays tracking to avoid unnecessary synchronization issues between the CPU and GPU, thereby improving system performance. The comparison experiment results show that the proposed algorithm improves the system performance by 2.7 times.

Параллельный алгоритм трассировки лучей для анализа поля излучения и построения обскурограмм излучающего газа

Параллельный алгоритм трассировки лучей для анализа поля излучения и построения обскурограмм излучающего газа

Imaging freeform optical systems designed with NURBS surfaces

The designs of two imaging freeform systems using nonuniform rational basis-spline (NURBS) optical surfaces are described. The first system, a 10 deg×9 degf/2 three-mirror anastigmat has four times higher spatial resolution over the image plane compared with the equivalent conventional rotational aspheric design, and 2.5 times higher resolution compared with a 10th-order XY polynomial freeform design. The mirrors for the NURBS freeform design have more than twice the asphericity than the conventional rotational and XY polynomial designs. In the second system, a Ritchey–Chretien telescope followed by a two-mirror NURBS freeform corrector is compared to a four-mirror Korsch telescope, for imaging to a visible-infrared imaging spectrometer. The freeform corrector design had 70% smaller spot sizes over the field and eliminated the large tertiary required in Korsch type design. Both of these NURBS freeform designs are possible due to a custom optical design code for fast accurate NURBS optimization, which now has parallel raytracing for thousands of NURBS grid points.

Parallel On-Demand Hierarchy Construction on Contemporary GPUs

We present the first parallel on-demand spatial hierarchy construction algorithm targeting ray tracing on many-core processors such as GPUs. The method performs simultaneous ray traversal and spatial hierarchy construction focused on the parts of the data structure being traversed. The method is based on a versatile framework built around a task pool and runs entirely on the GPU. We show that the on-demand construction can improve rendering times compared to full hierarchy construction. We evaluate our method on both object (BVH) and space (kd-tree) subdivision data structures and compare them mutually. The on-demand method is particularly beneficial for rendering large scenes with high occlusion. We also present SAH kd-tree builder that outperforms previous state-of-the-art builders running on the GPU.

A fast and efficient adaptive parallel ray tracing based model for thermally coupled surface radiation in casting and heat treatment processes

A new algorithm for heat exchange between thermally coupled diffusely radiating interfaces is presented, which can be applied for closed and half open transparent radiating cavities. Interfaces between opaque and transparent materials are automatically detected and subdivided into elementary radiation surfaces named tiles. Contrary to the classical view factor method, the fixed unit sphere area subdivision oriented along the normal tile direction is projected onto the surrounding radiation mesh and not vice versa. Then, the total incident radiating flux of the receiver is approximated as a direct sum of radiation intensities of representative “senders” with the same weight factor. A hierarchical scheme for the space angle subdivision is selected in order to minimize the total memory and the computational demands during thermal calculations. Direct visibility is tested by means of a voxel-based ray tracing method accelerated by means of the anisotropic Chebyshev distance method, which reuses the computational grid as a Chebyshev one. The ray tracing algorithm is fully parallelized using MPI and takes advantage of the balanced distribution of all available tiles among all CPU's. This approach allows tracing of each particular ray without any communication. The algorithm has been implemented in a commercial casting process simulation software. The accuracy and computational performance of the new radiation model for heat treatment, investment and ingot casting applications is illustrated using industrial examples.

A fast ray tracing algorithm based on a hybrid structure

This paper proposes a new group-based accelerating structure called hybrid structure for the ray tracing of dynamic scenes, whose main advantage is that we can choose a suitable local accelerating structure for each object in the scene. In the hybrid structure, the objects in the scene are organized into a hierarchical bounding volume structure by surface area heuristic (SAH) cost model with each object group node including only one object, and a local accelerating structure is constructed for each object. For a hybrid structure, a scene is divided into static part and dynamic part by the movement, and only dynamic part is updated in each frame. In addition, we design an efficient storage format according to the graphics processing unit (GPU) storage characteristics, which makes it easy to realize the parallel ray tracing on GPU. Experimental results show that the hybrid structure is efficient to deal with the dynamic scene including different kinds of objects, and it can be easily integrated into parallel application systems.

Acceleration of ray tracing method using predictive evaluation and GPGPU technology

Abstract Ray tracing is one of computer graphics methods for achieving the most realistic outputs. Its main disadvantage is high computation demands. Removal of this disadvantage is possible using parallelization due to the fact that the ray tracing method is inherently parallel. Solution presented in this article uses GPGPU (general-purpose computing on graphics processing units) technology and a predictive evaluation for the acceleration of ray tracing method. The CUDA C was selected as a GPGPU language and it was used for a conversion of a raytracer core. The main reason for choosing this language was usage of the Tesla C1060 graphics card. The predictive evaluation of a scene was based on the fact that total computation time increases proportionally with resolution. This evaluation allows selection of the optimal scene division for the parallel ray tracing. In tests, proposed GPGPU solution reached accelerations up to 28.3× comparing to CPU.

Enhancing Visual Rendering on Multicore Accelerators with Explicitly Managed Memories

Recent electronic devices are equipped with processors extended with multicore accelerators to take advantage of the powerful performance from acceleration co-processors. Applications on such high-end electronic products require capability to run graphic-rich applications. Scalable acceleration co-processors are frequently designed as multicores with explicitly managed memories. Such multicore architectures require sophisticated data management among the main memory and the local memories to fully exploit their potential performance. Ray tracing is a high quality rendering algorithm in computer graphics and has potentially many parallelism to exploit. On the explicitly managed memory hierarchies, however, ray tracing with complex data structures tends to suffer from irregular memory accesses and inefficient data management. Compared to other acceleration structures for ray tracing, grid structure is simple to manage but commonly regarded to produce too slow algorithms. However, recent improvements on grid structure with SIMD optimizations show comparable performance with kd-tree structure, which is one of the fastest acceleration structures. We introduce a grid structure based parallel ray tracer on a processor with a multicore accelerator. We adopt SIMD optimizations and double buffering to enhance the performance of grid-based ray tracer and propose a macrocell structure over the grid to fully exploit the memory bandwidth. In our experiment, our ray tracing scheme shows comparable performance with BVH-based ray tracer.

All sky CMB map from cosmic strings integrated Sachs-Wolfe effect

By actively distorting the cosmic microwave background (CMB) over our past light cone, cosmic strings are unavoidable sources of non-Gaussianity. Developing optimal estimators able to disambiguate a string signal from the primordial type of non-Gaussianity requires calibration over synthetic full sky CMB maps, which until now had been numerically unachievable at the resolution of modern experiments. In this paper, we provide the first high resolution full sky CMB map of the temperature anisotropies induced by a network of cosmic strings since the recombination. The map has about 200 million subarcminute pixels in the healpix format which is the standard in use for CMB analyses (${N}_{\mathrm{side}}=4096$). This premiere required about 800 000 cpu-hours; it has been generated by using a massively parallel ray tracing method piercing through thousands of state of art Nambu-Goto cosmic string numerical simulations which pave the comoving volume between the observer and the last scattering surface. We explicitly show how this map corrects previous results derived in the flat sky approximation, while remaining completely compatible at the smallest scales.

Ray tracing on a networked processor array

As computation costs increase to meet design requirements for computation-intensive graphics applications on today's embedded systems, the pressure to develop high-performance parallel processors on a chip will increase. Acceleration of the ray tracing computation has become a major issue as the computer graphics industry demands for rendering realistic images. Network-on-chip (NoC) techniques that interconnect multiple processing elements with routers are the solution for reducing computation time and power consumption by parallel processing on a chip. It is also essential to meet the scalability and complexity challenges for system-on-chip (SoC). In this article, we describe a parallel ray tracing application mapping on a mesh-based multicore NoC architecture. We describe an optimised ray tracing kernel and parallelisation strategies, varying the workload distribution statically and dynamically. In this work, we present results and timing performance of our parallel ray tracing application on a NoC, which are obtained through our cycle accurate multicore NoC simulator. Using a dynamic scheduling load balancing technique, we achieved a maximum speedup multiplier of 35.97 on an 8 × 8 networked processor array using a NoC as the interconnect.

Parallel radio-wave propagation modeling with image-based ray tracing techniques

Ray tracing is a technique based on the numerical simulation of geometrical optics and the uniform theory of diffraction, two well-known approximate methods for estimating a high-frequency electromagnetic field, based on the ray theory of field propagation. Radio-wave propagation prediction models based on ray tracing play an important role in wireless network planning, as they take into account diverse physical phenomena such as reflection, diffraction and foliage attenuation and are considered critical for the analysis of long term evolution (LTE) systems, which requires a detailed description of the wireless channel. A major practical drawback of these models is that they can easily become very computationally expensive, as the required level of accuracy and the corresponding areas of study increase. In this paper, a parallel ray tracing algorithm for radio-wave propagation prediction based on the electromagnetic theory of images is presented. The implementation of the algorithm is based on the message passing interface (MPI). The decomposition of the problem is conducted by partitioning the image tree, while dynamic load balancing techniques are employed by means of the master–worker and the work–pool patterns. The performance of the parallel implementation is studied for different problems and task assignment schemes, showing that high speedups can be achieved.

Exploring Multiprocessor Design and Implementation Issues with In-Class Demonstrations

This paper outlines the use of in-class demonstrations to aid students in appreciating hardware and software concepts related to multiprocessing in an upper-year undergraduate course on compuer system architecture. The demonstrations include visualization of cache coherence behavior, remote login to a multiprocessor server to demonstrate parallel program execution, observation of internal behavior of a single-chip multiprocessor implemented in a programmable logic chip, and the use of parallel ray-tracing software to visualize speedup and load balance on a multicore desktop computer. The heavy use of visualization seeks to ensure student interest and attention.

EXPERIENCES WITH MESH-LIKE COMPUTATIONS USING PREDICTION BINARY TREES ∗

In this paper we aim at exploiting the temporal coherence among successive phases of a computation, in order to implement a load-balancing technique in mesh-like computations to be mapped on a cluster of processors. A key concept, on which the load balancing schema is built on, is the use of a Predictor component that is in charge of providing an estimation of the unbalancing between successive phases. By using this information, our method partitions the computation in balanced tasks through the Prediction Binary Tree (PBT). At each new phase, current PBT is updated by using previous phase computing time for each task as next-phase's cost estimate. The PBT is designed so that it balances the load across the tasks as well as reduces dependency among processors for higher performances. Reducing dependency is obtained by using rectangular tiles of the mesh, of almost-square shape (i. e. one dimension is at most twice the other). By reducing dependency, one can reduce inter-processors communication or exploit local dependencies among tasks (such as data locality). Furthermore, we also provide two heuristics which take advantage of data-locality. Our strategy has been assessed on a significant problem, Parallel Ray Tracing. Our implementation shows a good scalability, and improves performance in both cheaper commodity cluster and high performance clusters with low latency networks. We report different measurements showing that tasks granularity is a key point for the performances of our decomposition/mapping strategy.

Parallel and Distributed Computing Techniques, Selection of papers from ISPDC 2008

Parallel and Distributed Computing Techniques, Selection of papers from ISPDC 2008