Ray Tracing Algorithm Research Articles

The Consistency of MJO Teleconnection Patterns on Interannual Time Scales

AbstractThe Madden–Julian oscillation (MJO) excites strong variations in extratropical geopotential heights that modulate extratropical weather, making the MJO an important predictability source on subseasonal to seasonal time scales (S2S). Previous research demonstrates a strong similarity of teleconnection patterns across MJO events for certain MJO phases (i.e., pattern consistency) and increased model ensemble agreement during these phases that is beneficial for extended numerical weather forecasts. However, the MJO’s ability to modulate extratropical weather varies greatly on interannual time scales, which brings extra uncertainty in leveraging the MJO for S2S prediction. Few studies have investigated the mechanisms responsible for variations in the consistency of MJO tropical–extratropical teleconnections on interannual time scales. This study uses reanalysis data, ensemble simulations of a linear baroclinic model, and a Rossby wave ray tracing algorithm to demonstrate that two mechanisms largely determine the interannual variability of MJO teleconnection consistency. First, the meridional shift of stationary Rossby wave ray paths indicates increases (decreases) in the MJO’s extratropical modulation during La Niña (El Niño) years. Second, a previous study proposed that the constructive interference of Rossby wave signals caused by a dipole Rossby wave source pattern across the subtropical jet during certain MJO phases produces a consistent MJO teleconnection. However, this dipole feature is less clear in both El Niño and La Niña years due to the extension and contraction of MJO convection, respectively, which would decrease the MJO’s influence in the extratropics. Hence, considering the joint influence of the basic state and MJO forcing, this study suggests a diminished potential to leverage the MJO for S2S prediction in El Niño years.

First generation of translucent monoliths for photochemical applications

AbstractMonolith structures are a common method to scale flow chemistry tools up to industrial throughput. Internally illuminated monolith reactors (IIMRs) were their versions for photochemistry. The channels inside the monolith were illuminated with optical fibers coated with a photocatalyst such as TiO2. The majority of the light in an IIMR was however not utilized to illuminate the reaction medium. Furthermore, the monolith was always made of opaque materials, making it impossible for unabsorbed light to illuminate other channels, lowering the photochemical space‐time yield (PSTY), a benchmark for the overall energy efficiency of a photoreactor. In this paper, the potential of a translucent monolith structure for scalable photochemical process design was tested. Due to the translucent nature of the monolith, there was no need for optical fibers or multiple light sources to provide the necessary photon flux and distribution. There has never been a study of translucent monoliths in the open literature and no design parameters have been investigated. This research studies the first translucent monoliths and their design principles by varying the channel size, channel distance as well as the amount of unit cells with a ray tracing algorithm in COMSOL Multiphysics. A model was developed, validated and used to design a monolith for the photodegradation of micropollutants in a case study. A theoretical improvement of seven orders of magnitude in PSTY was obtained compared to IIMRs making this reactor design a promising candidate for more efficient photochemical processes.

Marine mobile wireless channel modeling based on improved spatial partitioning ray tracing

In 5G era, it is expected to achieve wireless network coverage including offshore areas. Modeling of marine wireless channels is the basis of constructing a marine communication system. In this paper, a communication scene between an unmanned aerial vehicle (UAV) and a boat is simulated to study the marine wireless channel. Firstly, an improved spatial partitioning ray tracing algorithm is proposed to track the propagation path of electromagnetic waves at sea surface. Secondly, a mobile channel is simulated and modeled based on the track results. Finally, a loss measurement is carried out in the coastal waters based on the simple wireless channel loss measuring platform, and a path loss propagation model is built. Then we compare the actual measurement data with the simulation results and find that the two are have good consistency, which further verifies the reliability of the simulation.

Incidence angles on cylindrical receivers of solar power towers

In order to decrease the levelized cost of energy (LCOE) of solar power towers, efficiencies of all components have to be analyzed and improved. Among them is receiver absorptivity, which depends on the angle of incidence of solar radiation. While cylindrical receivers consist of arrays of vertical tubes, they are usually represented as flat surfaces for the optical part of simulations, imposing different incidence angles. Ray tracing and analytical algorithms for both primary and secondary absorption are used to compare absorptivity values for a detailed tube geometry with the simplified approach. Moreover the effect of horizontal aim point shifting on absorptivity is investigated. Results show that assuming flat surfaces leads to an underprediction of absorptivity of several tenths of a percentage point. A smaller overprediction of the same order of magnitude is reached for assuming entirely perpendicular incidence. Furthermore it is found that spillage losses due to horizontal aim point shifting exceed the effect of implied lower incidence angles by more than one order of magnitude.

Dual-precision fixed-point arithmetic for low-power ray-triangle intersections

Ray-Triangle intersection is a fundamental computation in most ray tracing algorithms. The prohibitive cost of the ray-triangle test algorithms limits the utilization of these algorithms in settings with low power budgets, such as mobile systems. In this work, we analyze the precision requirements for ray-triangle intersection and observe that for most of the rays a low fixed-point precision is sufficient and only for a small fraction of rays a high precision is required. Accordingly, we propose a dual-precision fixed-point hardware accelerator for ray-triangle intersection targeting low-power systems, where the higher precision is only activated for tests deemed critical by our algorithm. Towards this goal, we develop a thresholding technique that autonomously switches between the lower and higher precisions, where the lower precision unit is used for the majority of the tests resulting in significant benefits in power consumption. We evaluate our methodology on a representative set of scenes and our proposed methodology in hardware. Our methodology introduces negligible accuracy errors in ray-triangle tests with an average of 0.25% misclassifications, while offering 87% savings in energy consumption compared to a baseline floating-point design and 27% savings compared to a high-precision fixed-point design.

2D anisotropic multicomponent Gaussian-beam migration under complex surface conditions

Elastic-wave migration in anisotropic media is a vital challenge, particularly for areas with irregular topography. Gaussian-beam migration (GBM) is an accurate and flexible depth migration technique, which is adaptable for imaging complex surface areas. It retains the dynamic features of the wavefield and overcomes the multivalued traveltimes and caustic problems of Kirchhoff migration. We have extended the GBM method to work for 2D anisotropic multicomponent migration under complex surface conditions. We use Gaussian beams to calculate the wavefield from irregular topography, and we use two schemes to derive the down-continued recorded wavefields. One is based on the local slant stack as in classic GBM, in which the PP- and PS-wave seismic records within the local region are directly decomposed into local plane-wave components from irregular topography. The other scheme does not perform the local slant stack. The Green’s function is calculated with a Gaussian beam summation emitted from the receiver point at the irregular surface. Using the crosscorrelation imaging condition and combining with the 2D anisotropic ray-tracing algorithm, we develop two 2D anisotropic multicomponent Gaussian-beam prestack depth migration (GB-PSDM) methods, i.e., using the slant stack and nonslant stack, for irregular topography. Numerical tests demonstrate that our anisotropic multicomponent GB-PSDM can accurately image subsurface structures under complex topography conditions.

In Situ Wireless Channel Visualization Using Augmented Reality and Ray Tracing.

This article presents a novel methodology for predicting wireless signal propagation using ray-tracing algorithms, and visualizing signal variations in situ by leveraging Augmented Reality (AR) tools. The proposed system performs a special type of spatial mapping, capable of converting a scanned indoor environment to a vector facet model. A ray-tracing algorithm uses the facet model for wireless signal predictions. Finally, an AR application overlays the signal strength predictions on the physical space in the form of holograms. Although some indoor reconstruction models have already been developed, this paper proposes an image to a facet algorithm for indoor reconstruction and compares its performance with existing AR algorithms, such as spatial understanding that are modified to create the required facet models. In addition, the paper orchestrates AR and ray-tracing techniques to provide an in situ network visualization interface. It is shown that the accuracy of the derived facet models is acceptable, and the overall signal predictions are not significantly affected by any potential inaccuracies of the indoor reconstruction. With the expected increase of densely deployed indoor 5G networks, it is believed that these types of AR applications for network visualization will play a key role in the successful planning of 5G networks.

Cellular automata ray tracing in two-dimensional aero-optical flow fields

<sec>For the supersonic flow field with large density fluctuation produced by the unsteady flow and turbulent large-scale structures, an effective method to obtain the beam path is to solve the ray equation. Then the optical path difference (OPD), Strehl ratio (SR), optical transmission function (OTF), etc. can be obtained to analyze the optical distortion, and the correction of aero optics effects can be realized to improve the optical system performance. Generally, when the refractive index distribution is arbitrary, the ray equation analytic solution is difficult to obtain.</sec> <sec>Cellular automata (CA) ray tracing algorithm is proposed in this paper for aero-optical calculation in the 2D discrete flow fields. Unlike numerically solving the ray equation (NSRE), the coordinate value and the offset angle are calculated according to the position and direction transformation rules in CA algorithm. The position transformation rule is used to obtain the end point of the beam vector and determine whether the offset angle needs calculating at each iteration, the direction transformation rule is to calculate the offset angles. Then the refractive index field is integrated along the beam path to obtain the optical path length (OPL). The OPD is calculated from OPL. In this paper, aero-optical calculation is based on two types of flow fields. The supersonic shear layer including supersonic mixing layer and boundary layer 2D density distribution is measured by the nano-tracer-based planar laser scattering (NPLS) technique. The supersonic flow field surrounding the optical dome is simulated based on detached-eddy simulation (DES).</sec><sec>The OPD<sub>rms</sub> and program running time quantitatively verify the calculation accuracy and high efficiency of CA. The results show that for the 2D supersonic NPLS flow field and the 2D supersonic flow field surrounding the optical dome, the calculation accuracy of CA is approximately equal to NSRE. Moreover, we find that the program running time of NSRE is about four times that of the CA algorithm, so the efficiency of ray tracing is effectively improved. Thus, the CA algorithm provides a new scheme for aero-optical calculation in the 2D supersonic flow field. Meanwhile, it also provides a guideline for the research on the ray tracing in 3D discrete aero-optical flow field.</sec>

Application of ray tracing algorithm based on intersection optimization in 3D interior design

Aiming at the problem that the current algorithm of lighting effect cannot achieve a good effect in 3D interior design, this paper proposes an algorithm based on multi algorithm fusion to realize lighting effect in 3D interior design. The algorithm first optimizes the intersection of patch, sphere and rectangle based on ray tracing algorithm, and then optimizes the optimization algorithm and the algorithm of lighting shadow at the same time, it is applied to the realization of lighting effect of 3D interior design. The simulation results show that the algorithm based on multi algorithm fusion is more ideal for the realization of 3D interior design lighting effect than the existing algorithm.

GPU-Based Dynamic Solar Potential Estimation Tool Using 3D Plans

Estimations of the solar potential from the building design files may affect placement considerations in favor of more sunlight reception that reduces the energy costs and saves the environment. In this study, a GPU based system (GPU-DSRM) is proposed to estimate direct and diffuse solar radiation aggregated on 3D structures at urban or individual scale. In the proposed approach, finite element method, back-face detection and ray-tracing algorithms are customized to run in parallel to reduce the execution time. Thus, real-time shadow analysis with adjustable sampling rate and time scale can be performed without compromising precision and accuracy of the estimations. The most important novel aspect of the study is that it can be used anywhere in the world without the need for meteorological data. Some of the test results obtained from a site with 10 buildings are presented in this paper that shows a speedup value of 45 with the new GPU-based implementation compared to the CPU-based model. The GPU-DSRM tool has also been compared with geometric tools in the literature. Solar energy potential analysis of building designs or existing urban formations can be completed faster and more precisely with this new approach.

Correlation analysis between the beam propagation and the vapor capillary geometry by machine learning

Low Coherence Interferometry allows for a direct inline measurement of the capillary depth during laser material processing. To enable a robust interpretation of the measurement results, a large number of influencing factors have to be considered. The geometry of the vapor capillary significantly affects the reflection behavior of the measuring radiation. Particularly, with capillary dimensions in the order of the magnitude of the measuring beam, scattering and absorption effects become significant. This paper describes the utilization of a ray tracing algorithm to analyze the beam propagation within the capillary. A keyhole generator and Machine Learning methods were applied for systematic investigations of the propagation of the measuring radiation and thus enabled an improved interpretation of capillary depth measurements.

Technical Note: A feasibility study on deep learning-based radiotherapy dose calculation.

Various dose calculation algorithms are available for radiation therapy for cancer patients. However, these algorithms are faced with the tradeoff between efficiency and accuracy. The fast algorithms are generally less accurate, while the accurate dose engines are often time consuming. In this work, we try to resolve this dilemma by exploring deep learning (DL) for dose calculation. We developed a new radiotherapy dose calculation engine based on a modified Hierarchically Densely Connected U-net (HD U-net) model and tested its feasibility with prostate intensity-modulated radiation therapy (IMRT) cases. Mapping from an IMRT fluence map domain to a three-dimensional (3D) dose domain requires a deep neural network of complicated architecture and a huge training dataset. To solve this problem, we first project the fluence maps to the dose domain using a broad beam ray-tracing (RT) algorithm, and then we use the HD U-net to map the RT dose distribution into an accurate dose distribution calculated using a collapsed cone convolution/superposition (CS) algorithm. The model is trained on 70 patients with fivefold cross validation, and tested on a separate 8 patients. It takes about 1s to compute a 3D dose distribution for a typical 7-field prostate IMRT plan, which can be further reduced to achieve real-time dose calculation by optimizing the network. The average Gamma passing rate between DL and CS dose distributions for the 8 test patients are 98.5% (±1.6%) at 1mm/1% and 99.9% (±0.1%) at 2mm/2%. For comparison of various clinical evaluation criteria (dose-volume points) for IMRT plans between two dose distributions, the average difference for dose criteria is less than 0.25Gy while for volume criteria is <0.16%, showing that the DL dose distributions are clinically identical to the CS dose distributions. We have shown the feasibility of using DL for calculating radiotherapy dose distribution with high accuracy and efficiency.

BLENDING FUNCTIONALLY DEFINED SURFACES

Smooth surfaces with perturbation functions for the creation of complex shapes are considered. The method for describing objects in three-dimensional scenes with a base surface and perturbation functions that have a compact description is proposed. One of the positive properties of functionally defined objects in comparison with other methods of specifying models is the simplicity and efficiency of their geometric transformations, in particular, three-dimensional morphing and collision detection of objects. The most common model for visualizing three – dimensional images is the polygonal approximation. Along with many advantages, this model has its drawbacks. By modeling real objects, an approximate polygonal model is constructed. To increase the image quality, itis often necessary to increase the number of polygons. An increasein the number of polygons results in an increase in rendering time and memory usage. Changing the scale of an object introduces additional problems because you cannot change quickly and efficiently the number of polygons for the object model. You can get rid of such shortcomings by applying analytical volume assignment and rasterization using ray-tracing algorithms. Analytical volume assignment does not require a large amount of memory. The problem of synthesis of realistic images is relevant for various simulators, virtual studios and three-dimensional games. Now, there are already works on visualization of functionally defined surfaces, but their application is limited to a rather narrow class of surfaces and slow visualization. The algorithms used are difficult to optimize, which also imposes restrictions on practical application. The paper proposes to use a special class of volumes, which are called "free forms". Each free form represents abase surface and a perturbation on that surface. The base surface and perturbation are given by polynomials of the second degree-quadrics. To achieve smoothness, the perturbation function is raised to the third degree. The aim of the work is to create an application that, according to a given analytical task, calculates the frame depth and surface normal in each pixel with the help of perturbation quadrics. This application should use the computing resources of the graphics processing units as much as possible. There have been attempts to create algorithms to visualize volumes given analytically, but most of them used only the CPU for calculations, and the processing time was too long for practical application. Moreover, these algorithms were not designed for parallel processing.In contrast, the proposed algorithm uses a graphics-processing unit for most of the calculations. In this case, the calculations on the graphics accelerator occur in parallel, and the method effectively uses this feature. Due to parallel processing and the absence of the need to transfer a large amount of data from the shared memory to the memory of the graphics accelerator, the speed of visualization increases compared to the option that uses only the CPU. The clock speed of processors in graphics accelerators is less than the CPU frequency. However, for a certain class of tasks performance using graphics accelerators will be better, due to the large number of processors.

Study of molten pool dynamics and porosity formation mechanism in full penetration fiber laser welding of Al-alloy

To study molten pool dynamics, root hump formation, periodic keyhole behavior in full penetration laser welding (FPLW) of aluminum alloy, a numerical simulation was carried out, in which volume of fluid (VOF) method and ray-tracing algorithm were adopted. A varied metallic vapor shear stress model was considered. Meanwhile a series of welding experiments on specimens being composed of aluminum alloy and quartz glass were conducted to analyze the porosity formation process. It was found that the over-heated sagging with low surface tension stagnated at the bottom side and solidified to form root hump. The dominant backward heat convection at the lower part can well explain the extreme spreading of molten pool at bottom surface. Periodic behavior of the keyhole was identified during quasi-steady stage. The porosity can be effectively suppressed in FPLW. Both the porosity ratio and average porosity number were reduced obviously. The main mechanism of porosity formation in FPLW is the collapse of the rear keyhole wall, mainly caused by bulges on the front keyhole wall. Bubble coalescence is responsible for large porosity size and coalescence efficiency depends on bubble size difference.

GPS: User Position Calculation Including Advanced Troposphere Delay Modeling

Objective of this project is to analyze and mitigate troposphere delays induced in GPS signals, which can result in very large position errors while estimating user position. The standard models currently present do not take into account all the various set of parameters or elements of the troposphere that can cause a significant delay. This project also includes study of troposphere propagation delays that improve the understanding of GPS signal propagation through the troposphere during irregular conditions. This characteristic is very important as it can play crucial role in real time surveying, navigation, precision farming and positioning for emergency services. Due to the tropical nature of the Indian climate the troposphere delay can be observed significantly in India sub-continent. In order to accurately estimate delay troposphere in real time conditions is taken into account, which are provided by the Indian meteorological department, by their automatic weather surveillance systems. GPS data for stations in India is obtained from CORS data for Bangalore, from where we obtain the observation and navigation files used in the calculations. Obtained data is processed and run through various algorithms like least squares satellite position calculation, error mitigation and ray tracing algorithms to mitigate troposphere and better estimate user position. Apart from these algorithms this project also includes a study on various concepts/formulas that help in using the forecasted real time data to be used in snell’s law to estimate delay as part of ray tracing techniques. All the code development in this project is done using MATLAB by math works and GUI is developed for an easier interface. For analysis purposes the data is analyzed with and without the advanced mitigation techniques to show the improvement in position estimation using advanced troposphere mitigation techniques.

Implications of 3D Seismic Raytracing on Focal Mechanism Determination

AbstractThe purpose of this study is to investigate apparent first‐motion polarities mismatch at teleseismic distances in the determination of focal mechanism. We implement and compare four seismic raytracing algorithms to compute ray paths and travel times in 1D and 3D velocity models. We use the raytracing algorithms to calculate the takeoff angles from the hypocenter of the 24 August 2016 Mw 6.8 Chauk earthquake (depth 90 km) in central Myanmar to the stations BFO, GRFO, KONO, and ESK in Europe using a 3D velocity model of the upper mantle below Asia. The differences in the azimuthal angles calculated in the 1D and 3D velocity models are considerable and have a maximum value of 19.6°. Using the takeoff angles for the 3D velocity model, we are able to resolve an apparent polarity mismatch where these stations move from the dilatational to the compressional quadrant. The polarities of synthetic waveforms change accordingly when we take the takeoff angles corresponding to the 3D model into account. This method has the potential to improve the focal mechanism solutions, especially for historical earthquakes where limited waveform data are available.

Development and prospective in-patient proof-of-concept validationof a surface photogrammetry+CT-based volumetric motion model for lung radiotherapy.

We develop and validate a motion model that uses real-time surface photogrammetry acquired concurrently with four-dimensional computed tomography (4DCT) to estimate respiration-induced changes within the entire irradiated volume, over arbitrarily many respiratory cycles. A research, couch-mounted, VisionRT (VRT) system was used to acquire optical surface data (15Hz, ROI=15×20cm2 ) from the thoraco-abdominal surface of a consented lung SBRT patient, concurrently with their standard-of-care 4DCT. The end-exhalation phase from the 4DCT was regarded as reference and for each remaining phase, deformation vector fields (DVFs) with respect to the reference phase were computed. To reduce dimensionality, the first two principal components (PCs) of the matrix of nine DVFs were calculated. In parallel, ten phase-averaged VRT surfaces were created. Surface DVFs and corresponding PCs were computed. A principal least squares regression was used to relate the PCs of surface DVF to those of volume DVFs, establishing a relationship between time-varying surface and the underlying time-varying volume. Proof-of-concept validation was performed during each treatment fraction by concurrently acquiring 30s time series of real-time surface data and "ground truth" kV fluoroscopic data (FL). A ray-tracing algorithm was used to create a digitally reconstructed fluorograph (DRF), and motion trajectories of high-contrast, soft-tissue, anatomical features in the DRF were compared with those from kV FL. For five of the six fluoroscopic acquisition sessions, the model out-performed 4DCT in predicting contour Dice coefficient with respect to fluoroscopy-derived contours. Similarly, the model exhibited a marked improvement over 4DCT for patch positions on the diaphragm. Model patch position errors varied from 5 to -15mm while 4DCT errors ranged between 5 and -22.4mm. For one fluoroscopic acquisition, a marked change in the a priori internal-external correlation resulted in model errors comparable to those of 4DCT. We described the development and a proof-of-concept validation for a volumetric motion model that uses surface photogrammetry to correlate the time-varying thoraco-abdominal surface to the time-varying internal thoraco-abdominal volume. These early results indicate that the proposed approach can result in a marked improvement over 4DCT. While limited by the duration of the fluoroscopic acquisitions as well as the resolution of the acquired images, the DRF-based proof-of-concept technique developed here is model-agnostic, and therefore, has the potential to be used as an in-patient validation tool for other volumetric motion models.

Scattering of light by dense particulate media in the geometric optics regime

We present a hybrid radiative transfer geometric optics approximation to model multiple light scattering in arbitrary finite discrete random media in the geometric optics regime. In the hybrid model, the medium is divided into a mantle composed of discrete particles and into a diffusely scattering core. In the mantle, multiple scattering is handled by using a ray-tracing algorithm with the generalized Snel’s law for inhomogeneous waves, whereas, in the core, ray tracing with diffuse scatterers is incorporated to approximate multiple scattering and absorption. The extinction distances required to compute the scattering in the core are derived numerically by tracing the distances of the scattering and absorption events instead of using the classical extinction mean free path length. We have written a new framework that can treat arbitrary meshes consisting of watertight surface meshes with multiple diffuse scatterers and refractive indices. Comparison between the “ground truth” obtained from pure geometric optics ray tracing, the solutions obtained by using radiative transfer, and the hybrid model show that the hybrid model can produce better results, particularly, if a densely-packed medium is studied. In the future, the new approximation could be used to solve light scattering from larger media, such as asteroid surfaces, that are out of reach for the pure geometric optics methods due to their computational complexity.

Image distortion correction method in a nonuniform temperature field by using Runge-Kutta ray tracing.

To solve the imaging distortion problem in a nonuniform temperature field for visual measurement, this paper studies the Runge-Kutta ray tracing algorithm. First, the light ray emitted by the spatial light point will be abstracted by the proposed method. Then, the ray trajectory in a 3D nonuniform temperature gradient environment will be reproduced, and the ray distortion can be corrected. Finally, the distortion is compared with the actual image distortion obtained through the corner detection method. The experimental results show that the correction method for the distortion image caused by nonuniform temperature gradient heat source interference is feasible by using the Runge-Kutta ray tracing algorithm, which can realize the error compensation for image distortion and obtain an accurate corrected image.

TURTLE: A C library for an optimistic stepping through a topography

TURTLE is a C library providing utilities allowing to navigate through a topography described by a Digital Elevation Model (DEM). The library has been primarily designed for the Monte Carlo transport of particles scattering over medium to long ranges, e.g. atmospheric muons. But, it can also efficiently handle ray tracing problems with very large DEMs (109 nodes or more), e.g. for neutrino simulations. The TURTLE library was built on an optimistic ray tracing algorithm, detailed in the present paper. This algorithm proceeds by trials and errors, approximating the topography within the modelling uncertainties of the DEM data. This allows to traverse a topography in constant time, i.e. independently of the number of grid nodes, and with no added memory. Detailed performance studies are provided by comparison to other ray tracing algorithms and as an application to muon transport in a Monte Carlo simulation. Program summaryProgram Title: The TURTLE libraryProgram Files doi:http://dx.doi.org/10.17632/pbnsctnbk8.1Licensing provisions: LGPL-3.0Programming language: C99Nature of problem: Transport long range Monte Carlo particles through a topography described by a high resolution Digital Elevation Model (DEM).Solution method: Mapping the ground surface on the fly using a heuristic requiring only the original DEM data.