Principle Of Ray Tracing Research Articles

Simulation of the Golay3 multiple mirror telescope with a conicoidal primary mirror by extending the optical design program

The notion of a sparse aperture system offers a novel solution to decrease the volumes and weight of space telescopes while pursuing higher resolutions. A simulation of the applicable sparse aperture systems is studied. First, the principle of ray tracing used in the optical design program is analyzed. It is pointed out that surface models representing the primary mirror of a sparse aperture system can be established by programming and creating Dynamic Link Library files to define the propagation properties of the passing rays. The method of simulating the Golay3 multiple mirror telescope (MMT) with a conicoidal primary mirror is proposed. Second, the structure of the conicoidal primary mirror of the Golay3 MMT is investigated. Formulas to define the directions, optical path lengths and intensities of rays passing through the primary mirror are deduced. Finally, two Golay3 MMT systems are simulated as examples. Their simulation results are presented and analyzed. The theoretical fill factors, the simulative fill factors, and the normalized modulation transfer functions of the simulated system are calculated to verify the proposed simulation method. They are proved to be in accordance with each other.

Forward Modelling and Detection of Gpr in Urban Road Base Disease

Ground penetrating radar is a high-resolution engineering geophysical method which has better detection effect to disengaging, cavities and leakiness in urban road base. This paper is based on the principle of ray tracing through the forward modelling of urban road base hollow, empty and not dense disease, analyses waveform, frequency, wave propagation characteristics of primary disease forward image simulation. The paper summarizes the urban road base diseases in ground penetrating radar profile feature of signal, and analyses field exploration radar profile and further research on primary diseases of urban road ground penetrating radar fingerprint for urban road base disease detection of ground penetrating radar data interpretation to provide the reference.

Accounting for partiality in serial crystallography using ray-tracing principles.

Serial crystallography generates `still' diffraction data sets that are composed of single diffraction images obtained from a large number of crystals arbitrarily oriented in the X-ray beam. Estimation of the reflection partialities, which accounts for the expected observed fractions of diffraction intensities, has so far been problematic. In this paper, a method is derived for modelling the partialities by making use of the ray-tracing diffraction-integration method EVAL. The method estimates partialities based on crystal mosaicity, beam divergence, wavelength dispersion, crystal size and the interference function, accounting for crystallite size. It is shown that modelling of each reflection by a distribution of interference-function weighted rays yields a `still' Lorentz factor. Still data are compared with a conventional rotation data set collected from a single lysozyme crystal. Overall, the presented still integration method improves the data quality markedly. The R factor of the still data compared with the rotation data decreases from 26% using a Monte Carlo approach to 12% after applying the Lorentz correction, to 5.3% when estimating partialities by EVAL and finally to 4.7% after post-refinement. The merging R(int) factor of the still data improves from 105 to 56% but remains high. This suggests that the accuracy of the model parameters could be further improved. However, with a multiplicity of around 40 and an R(int) of ∼50% the merged still data approximate the quality of the rotation data. The presented integration method suitably accounts for the partiality of the observed intensities in still diffraction data, which is a critical step to improve data quality in serial crystallography.

Research on Outdoor Positioning Based on Ray Tracing Method

GPS can’t detect the signal because of the cell complex environment in the outdoor and poor radio wave propagation conditions, so that the positioning result is not ideal. However, the positioning method using the ray tracing prediction of radio waves, the tracking point of the scene from all the source radiation, record the relevant parameters, and then positioned within the microcell environment can satisfy the demand. The principle of ray tracing was firstly introduced in this paper, then an outdoor positioning model was set up, finally, the corresponding simulation experiments was implemented to demonstrate the effectiveness of ray tracing positioning in the outdoor environments.

GeoViS—Relativistic ray tracing in four-dimensional spacetimes

The optical appearance of objects moving close to the speed of light or orbiting a black hole is of interest for educational purposes as well as for scientific modeling in special and general relativity. The standard approach to visualize such settings is ray tracing in four-dimensional spacetimes where the direction of the physical propagation of light is reversed. GeoViS implements this ray tracing principle making use of the Motion4D library that handles the spacetime metrics, the integration of geodesics, and the description of objects defined with respect to local reference frames. In combination with the GeodesicViewer, GeoViS might be a valuable tool for graduate students to get a deeper understanding in the visual effects of special and general relativity. Program summaryProgram title: GeoViSCatalogue identifier: AESY_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AESY_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 241796No. of bytes in distributed program, including test data, etc.: 1667246Distribution format: tar.gzProgramming language: C++, Scheme.Computer: Linux platforms.Operating system: Linux.Has the code been vectorized or parallelized?: Yes, Parallelized using MPI.RAM: ?? BytesClassification: 1.5.External routines: Gnu Scientific Library (GSL), Motion4D, MPI.Nature of problem:First-person visualization of four-dimensional spacetimes in the theory of relativity.Solution method:Integration of ordinary differential equations for ray tracing.Running time:Scene dependent—from seconds to hours.

A Holistic Virtual Laboratory on Wireless Communications and Sensor Networks

Virtual laboratories have evolved into an adequately mature educational tool for multiple fields of study. Their use is especially beneficial to modern topics such as modern wireless communications. Related solutions in this field explored various approaches and architectures in designing such a virtual environment. The presented software package combines these fragmentary conclusions to a holistic and extensible laboratory architecture. Classic and modern topics, such as propagation, green networking, indoor communications and sensor networks are discussed through interactive 2D/3D environments. The student is also introduced to field measurement procedures and ray tracing principles. Statistical assessment in the context of a postgraduate course in wireless communications demonstrates the educational benefits of the approach.

Identifying the directions of a set of 2D contours for additive manufacturing process planning

Additive Manufacturing (AM) is a process in which material is added layer by layer to build a physical part. In AM process planning, a stack of 2D closed contours is obtained when a 3D stereolithography (STL) model is sliced. Each slice may have a set of closed contours or polygons, each of which needs to be classified (oriented) as internal (clockwise) or external (counterclockwise) to identify where material should be added. This is not a straightforward task as the STL format does not ensure correct surface orientation of the 3D model. This work describes two methods for identifying the direction of each contour in a set, i.e., for sorting them into internal and external contours. Three alternative tests to check whether a point is inside or outside a polygon were evaluated. The tests are based on the ray-tracing principle and the classical point-in-polygon test. The proposed algorithms were devised and implemented in an AM process planning system. The methods were validated using 3D models with a variety of geometries, and the computing time for the alternative tests was compared. The results showed that the method based on the point-in-polygon tests has some advantages.

RAY-OPTICS ANALYSIS OF SINGLE MODE CONDITION FOR OPTICAL WAVEGUIDES WITH RECTANGULAR CROSS-SECTION

The single mode condition of rectangular waveguides is derived by using a simple ray-optics approach, which relies on geometrical ray tracing principles as in classical optics. Light propagation through such a waveguide can be approximately simplifled as re∞ections within two planes of incidence. By employing the mode equations for difierent polarizations, a relation that shows the single- mode cut-ofi as a function of the waveguide dimensions is readily obtained.

An optical design and simulation of LED low-beam headlamps

The low-beam headlamp is an important component for the automobile safety. With the improvement of optical efficiency and heat dissipation' technology of white LEDs, it becomes feasible to design low-beam headlamps with LEDs. The principle of B-spline surfaces is used to construct the free-form surface reflector meeting the requirement. First, the initial B-spline surface reflector is established on the basis of the light source structure, emitting features and capability of light distribution. Optical simulation is carried out according to the principle of ray tracing. And then the simulation results will be compared with the standard of photometric characteristics. The segmented surfaces fine-tuning method and the method of trial and error are used to trim the part that failed to meet requirements gradually. The vector groups of surfaces are obtained. Finally,the desired free-form surface reflector meeting the ECE regulations is got. The experimental results can meet the standard of photometric characteristics. The impact of the technique showed in this paper in the field of LED illumination design seems to be a very promising topic.

A Novel X-ray Diffraction –based Technique for Complete Stress State Mapping of Packaged Silicon Dies

AbstractFundamental understanding of the silicon stresses and their changes with traditional wire-bonded and flip chip packages is critical to address the performance and reliability improvements in new technologies. Recently we have developed a novel technique for non-destructive measurements of complete strain state (and thereby the stress state) of the single crystal (bulk Si) by tracing the relative change in direction of an x-ray beam diffracted from a stressed crystal. This is based on the relationship between the stress state in a crystal and the local lattice plane orientation. Experimentally, this can be achieved by using a large area synchrotron white beam in conjunction with a precision grid of x-ray absorbing material placed in the path of the beam. The grid breaks the X-ray beam into an array of micro-beams that are diffracted by the single crystal sample to produce an integrated x-ray topograph on which the inverse grid image is distorted due to changes in the paths of diffracted microbeams i.e. an x-ray reticulograph is created. The distortions are a result of the variations in the diffracting lattice plane orientation produced by strain present in the crystal. By measuring this distortion on multiple topographs through the electronic package and applying the ray tracing principle, the entire strain state of the silicon can be calculated and mapped for the entire sample. We have carried out stress mapping of the silicon device in the package by applying this non-destructive and non-invasive technique.

Synchrotron X-Ray Topographic Studies of Recombination Activated Shockley Partial Dislocations in 4H-Silicon Carbide Epitaxial Layers

Electron-hole recombination activated Shockley partial dislocations bounding expanding stacking faults and their interactions with threading dislocations have been studied in 4H-SiC epitaxial layers using synchrotron x-ray topography. The bounding partials appear as white stripes or narrow dark lines in back-reflection X-ray topographs recorded using the basal plane reflections. Such contrast variations are attributable to the defocusing/focusing of the diffracted X-rays due to the edge component of the partial dislocations, which creates a convex/concave distortion of the basal planes. Simulation results based on the ray-tracing principle confirm our argument. The sign of the partial dislocations can be subsequently determined.

Determination of the Core-structure of Shockley Partial Dislocations in 4H-SiC

ABSTRACTSynchrotron x-ray topographs taken using basal plane reflections indicate that the electron-hole recombination activated Shockley partial dislocations in 4H silicon carbide bipolar devices appear as either white stripes with dark contrast bands at both edges or dark lines. In situ electroluminescence observations indicated that the mobile partial dislocations correspond to the white stripes in synchrotron x-ray topographs, while immobile partial dislocations correspond to the dark lines. Computer simulation based on ray-tracing principle indicates that the contrast variation of the partial dislocations in x-ray topography is determined by the position of the extra atomic half planes associated with the partial dislocations lying along their Peierls valley directions. The chemical structure of the Shockley partial dislocations can be subsequently determined unambiguously and non-destructively.

Investigation of Electron–Hole Recombination-Activated Partial Dislocations and Their Behavior in 4H-SiC Epitaxial Layers

Electron-hole recombination-activated partial dislocations in 4H silicon carbide homoepitaxial layers and their behavior have been studied using synchrotron X-ray topography and electroluminescence. Stacking faults whose expansion was activated by electron-hole recombination enhanced dislocation glide were observed to be bounded by partial dislocations, which appear as white stripes or narrow dark lines in back-reflection X-ray topographs recorded using the basal plane reflections. Such contrast variations are attributable to the defocusing/focusing of the diffracted X-rays due to the edge component of the partial dislocations, which creates a convex/concave distortion of the basal planes. Simulation results based on the ray-tracing principle confirm our argument. Observations also indicate that, when an advancing partial dislocation interacts with a threading screw dislocation, a partial dislocation dipole is dragged behind in its wake. This partial dislocation dipole is able to advance regardless of the immobility of the C-core segment. A kink pushing mechanism is introduced to interpret the advancement of this partial dislocation dipole.

Comparison of laser ray-tracing and skiascopic ocular wavefront-sensing devices

To compare two wavefront-sensing devices based on different principles. Thirty-eight healthy eyes of 19 patients were measured five times in the reproducibility study. Twenty eyes of 10 patients were measured in the comparison study. The Tracey Visual Function Analyzer (VFA), based on the ray-tracing principle and the Nidek optical pathway difference (OPD)-Scan, based on the dynamic skiascopy principle were compared. Standard deviation (SD) of root mean square (RMS) errors was compared to verify the reproducibility. We evaluated RMS errors, Zernike terms and conventional refractive indexes (Sph, Cyl, Ax, and spherical equivalent). In RMS errors reading, both devices showed similar ratios of SD to the mean measurement value (VFA: 57.5+/-11.7%, OPD-Scan: 53.9+/-10.9%). Comparison on the same eye showed that almost all terms were significantly greater using the VFA than using the OPD-Scan. However, certain high spatial frequency aberrations (tetrafoil, pentafoil, and hexafoil) were consistently measured near zero with the OPD-Scan. Both devices showed similar level of reproducibility; however, there was considerable difference in the wavefront reading between machines when measuring the same eye. Differences in the number of sample points, centration, and measurement algorithms between the two instruments may explain our results.

Basic design of beamline and polarization control

The basic concept of synchrotron radiation beamlines for vacuum ultraviolet and X-ray experiments has been introduced to beginning users and designers of beamlines. The beamline defined here is composed of a front end, pre-mirrors, and a monochromator with refocusing mirrors, which are connected by beam pipes, providing monochromatic light for the experiments. Firstly, time characteristics of the synchrotron radiation are briefly reviewed. Secondly, the basic technology is introduced as the fundamental knowledge required to both users and designers. The topics are photoabsorption by air and solids, front ends and beam pipes, mirrors, monochromators, and filters. Thirdly, the design consideration is described mainly for the designers. The topics are design principle, principle of ray tracing, optical machinery and control, and vacuum. Fourthly, polarization control is considered. The topics are polarizers, polarization diagnosis of beamline, and circularly-polarized light generation. Finally, a brief summary is given introducing some references for further knowledge of the users and the designers.

Accuracy and Reproducibility of Zywave, Tracey, and Experimental Aberrometers

To compare the accuracy and verify the reliability of different commercial and experimental prototypes of aberrometers using a small group of normal subjects with low myopia. Three different devices were used to measure the wavefront aberration of five normal myopic eyes: 1) Zywave--commercial aberrometer based on a Hartmann-Shack wavefront sensor; 2) Tracey--commercial system based on the laser ray tracing principle; and 3) an experimental laboratory laser ray tracing instrument working at two different wavelengths (532 and 786 nm). A series of five measurements were taken for each subject. Pupil diameter and alignment were controlled. All wave aberration maps were reduced to a common 6.5-mm pupil diameter, and then the mean and standard deviation were computed for the series, as well as the global average and standard deviation for each subject. Despite several important differences among devices and sessions, the results obtained with the different devices were equivalent. The main difference found between aberrometers was due to the longitudinal chromatic aberration caused by the use of different wavelengths. The signal-to-noise ratio estimated from the raw data was moderate, 12, but could be improved by a factor of 2 by discarding those measurements with a higher deviation from the mean and averaging the remaining data, which was the approach implemented in the Zywave instrument. The aberrometers tested were reliable in normal eyes with low myopia. Aberrometry is a robust but noisy technique. Accuracy is limited by noise and other sources of variability, including the size and alignment of the pupil. These conclusions might not apply to eyes with large aberrations.

Integrated 3D Display of Brain Anatomy and Intracranial Vasculature in MR Imaging

In many clinical situations neuroradiologists and neurosurgeons are keenly interested in images displaying both brain structures and intracranial vessels in an integrative manner. In this paper an approach to three-dimensional visualization of brain and vascular structures from magnetic resonance (MR) volume data is reported. It has been designed with the aim of providing a robust and reliable image processing tool for routine clinical applications. The method has been made possible by recent developments in MR image acquisition, especially MR angiography and rapid gradient-echo sequences (Turbo-fast low angle shot). On the basis of the ray-tracing principle, integration of brain and vessel anatomy into a single 3D image is achieved. Image data are acquired with flow-compensated gradient-echo pulse sequences. Even slow flow in venous structures may be demonstrated using a two-dimensional sequential-slice scanning method. Finally, if incorporated into an interactive image processing system, this technique may be used as a planning tool allowing a surgical "rehearsal" prior to actual operative exposure and resection of a lesion.

Who invented ray tracing?

We provide some remarks on the very early developments of the visualization techniques conducted during the European Renaissance. It is shown that the basic principle of ray tracing was already presented by Albrecht Durer (1471–1528) in 1525. This article is intended to be of common interest; it is not a scientific report.

Polarized light scattering by hexagonal ice crystals: theory

A scattering model involving complete polarization information for arbitrarily oriented hexagonal columns and plates is developed on the basis of the ray tracing principle which includes contributions from geometric reflection and refraction and Fraunhofer diffraction. We present a traceable and analytic procedure for computation of the scattered electric field and the associated path length for rays undergoing external reflection, two refractions, and internal reflections. We also derive an analytic expression for the scattering electric field in the limit of Fraunhofer diffraction due to an oblique hexagonal aperture. Moreover the theoretical foundation and procedures are further developed for computation of the scattering phase matrix containing 16 elements for randomly oriented hexagonal crystals. Results of the six independent scattering phase matrix elements for randomly oriented large columns and small plates, having length-to-radius ratios of 300/60 and 8/10 microm, respectively, reveal a number of interesting and pronounced features in various regions of the scattering angle when a visible wavelength is utilized in the ray tracing program. Comparisons of the computed scattering phase function, degree of linear polarization, and depolarization ratio for randomly oriented columns and plates with the experimental scattering data obtained by Sassen and Liou for small plates are carried out. We show that the present theoretical results within the context of the geometric optics are in general agreement with the laboratory data, especially for the depolarization ratio.

Calculation of reverberation and average intensity of broad-band acoustic signals in the ocean by means of the RAIBAC computer model

Based on the conventional ray-tracing principle, a fast numerical algorithm is developed that calculates averaged propagation loss and reverberation of underwater sound. The averaging is performed by summing incoherently the contributions of individual ray bundles to each of the rectangular cells into which the range/depth plane is divided. The resulting matrix description of the average intensity field is used to calculate reverberation. The propagation-loss algorithm is preliminarily tested against mathematical test functions and measured data. Subject Classification: [43]30.20, [43]30.40; [43]85.84.