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Photorealistic volume scattering model in the bidirectional stochastic ray tracing problem

PROGRAMMING AND COMPUTER SOFTWARE 2015年第5期41卷 295-301页

作者： Zhdanov, D. D. Garbul, A. A. Potemin, I. S. Voloboy, A. G. Galaktionov, V. A. Ershov, S. V. Sokolov, V. G. St Petersburg Natl Res Univ Informat Technol Mech St Petersburg 197101 Russia Russian Acad Sci Keldysh Inst Appl Math Moscow 125047 Russia Vavilov State Opt Inst St Petersburg 99053 Russia

This paper is devoted to the development of physically correct rendering model of scenes containing volume scattering objects. The solution of the rendering equation is based on the Monte-Carlo bidirectional ray tracing. Two efficient approaches to the solution of the rendering equation for different parameters of the volume scattering medium (typically, concentration of scattering particles) are developed. Examples illustrate how the proposed models can be used for photorealistic visualization of scenes containing volume scattering objects and for the simulation of illuminators based on the volume scattering effect. Possible limitations of the application field of the proposed models are considered.

关键词： ray tracing algorithms COMPUTER algorithms SCATTERING (Mathematics) MONTE Carlo method MATHEMATICAL models RESEARCH

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Three-Dimensional Radiation ray-tracing for Shock-Layer Radiative Heating Simulations

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JOURNAL OF SPACECRAFT AND ROCKETS 2013年第3期50卷 485-493页

作者： Mazaheri, Alireza Johnston, Christopher O. Sefidbakht, Siavash NASA Langley Res Ctr Aerothermodynam Branch Hampton VA 23681 USA NASA Langley Res Ctr Hampton VA 23681 USA

A three-dimensional ray-tracing algorithm is developed for shock-layer radiative heating predictions. When coupled with a tangent slab approximate code, such as the HARA radiation code, this algorithm provides an efficient approach for computing the radiative heating and allows the commonly applied tangent slab approximation to be removed. Application to several Earth- and Mars-entry conditions show that the ray-tracing approach predicts up to 15% lower radiative heating values than the tangent slab approximation at the stagnation point, which is consistent with the results of previous studies. In the afterbody region of Mars entry vehicles, where radiative heating from the CO2 molecule may be larger than convective heating, a 70% reduction from the tangent-slab result is seen, indicating the inadequacy of the tangent slab approximation in such regions.

关键词： ray tracing algorithms algorithms (Physics) HEAT -- Radiation & absorption HEAT -- Convection ATMOSPHERIC entry of space vehicles MARS (Planet) SPACE vehicles -- Thermodynamics

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ray-tracing intraocular lens power calculation using anterior segment optical coherence tomography measurements

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JOURNAL OF CATARACT AND REFRACTIVE SURGERY 2012年第10期38卷 1758-1763页

作者： Minami, Keiichiro Kataoka, Yasushi Matsunaga, Jiro Ohtani, Shinichiro Honbou, Masato Miyata, Kazunori Miyata Eye Hosp Miyakonojo Miyazaki Japan

PURPOSE: To assess the efficiency of ray-tracing intraocular lens (IOL) power calculation with anterior segment optical coherence tomography (AS-OCT) in normal eyes with cataract. SETTING: Miyata Eye Hospital, Miyakonojo, Miyazaki, Japan. DESIGN: Case series. METHODS: The study comprised consecutive patients who had cataract surgery and obtained a corrected visual acuity of 0.15 logMAR or better postoperatively. Preoperatively, Placido topography and AS-OCT measurements were taken during a routine examination. The predicted postoperative refractions were obtained using 3 methods: the SRK/T formula with autokeratometry, ray-tracing calculation with Placido topography data, and ray-tracing calculations with AS-OCT measurement of both corneal surfaces. The refractive errors from the manifest refraction spherical equivalent were compared 1 month postoperatively, and the effects of corneal eccentricity and posterior corneal curvature were evaluated. RESULTS: Seventy patients (102 eyes) were enrolled. There was no significant difference in refractive errors (P=.89). The refractive error with the SRK/T formula was correlated significantly with corneal eccentricity (P=.0017);the ray-tracing calculations were unaffected. There was a weak correlation with the posterior corneal curvature in the ray-tracing calculations performed with Placido topography (P<.0002). CONCLUSION: The accuracy of the ray-tracing IOL power calculations using AS-OCT data was comparable to that of the conventional formula and minimized the effect of corneal eccentricity and posterior corneal curvature.

关键词： INTRAOCULAR lenses ray tracing algorithms OPTICAL coherence tomography CATARACT surgery VISUAL acuity POSTOPERATIVE period EYE -- Refractive errors

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Optical ray tracing-guided laser in situ keratomileusis for moderate to high myopic astigmatism

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JOURNAL OF CATARACT AND REFRACTIVE SURGERY 2012年第1期38卷 28-34页

作者： Schumacher, Silvia Seiler, Theo Cummings, Arthur Maus, Matthias Mrochen, Michael Inst Refrakt & Ophthalmochirurg Zurich Switzerland Wellington Eye Clin Dublin Ireland Sehkraft Augenzentrum Maus Cologne Germany

PURPOSE: To assess the efficacy, safety, and predictability of an individualized laser in situ keratomileusis (LASIK) ablation profile based on an optical ray-tracing algorithm to treat moderate to high myopic astigmatism. SETTING: Ophthalmology centers in Zurich, Switzerland;Dublin, Ireland;and, Cologne, Germany. DESIGN: Multicenter clinical trail. METHODS: This 3-center study enrolled eyes with a manifest refraction sphere ranging from 0.50 to -10.25 diopters (D) and/or astigmatism ranging from 0.00 to -4.50 D. The intended outcome was piano in most eyes, undercorrection of 0.50 D in 1 eye, and undercorrection of 0.25 D in 2 eyes. Refractive outcomes were analyzed preoperatively and postoperatively at 1 day and 1 and 3 months. RESULTS: The study enrolled 127 eyes (71 patients). The mean manifest refraction was -5.92 D +/- 1.72 (SD). By 3 months postoperatively, 15 eyes had been lost to follow-up and 1 eye was excluded from analysis because of early retreatment. Of the remaining 111 eyes, 93 (83.8%) had an uncorrected distance visual acuity (UDVA) of 20/20 or better. The mean manifest refraction spherical equivalent (MRSE) in all eyes was 0.03 +/- 0.30 D. In 97 (87.4%), the MRSE was within 0.50 D and in 107 (96.4%), within +/- 1.00 D. No eye lost 2 or more lines of corrected distance visual acuity. CONCLUSIONS: The new optical ray-tracing algorithm for individualized LAM ablation profiles to treat moderate to high myopic astigmatism was efficacious, safe, and predictable. The UDVA in eyes with high myopic astigmatism was better than in those treated with wavefront-guided LASIK.

关键词： LASIK (Eye surgery) EYE -- Laser surgery ASTIGMATISM MYOPIA ABLATION techniques (Medicine) ray tracing algorithms

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Customized aspheric intralocular lenses calculated with real ray tracing

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JOURNAL OF CATARACT AND REFRACTIVE SURGERY 2009年第11期35卷 1984-1994页

作者： Einighammer, Jens Oltrup, Theo Feudner, Elisabeth Bende, Thomas Jean, Benedikt Univ Tubingen Hosp Ctr Ophthalmol Inst Ophthalm Res Sect Expt Ophthalm Surg D-72072 Tubingen Germany

PURPOSE: To calculate the exact geometry of custom intraocular lenses (IOLs) for pseudophakic eyes and theoretically predict the residual wavefront error by real ray tracing based on Snell's law. SETTING: Centre for Ophthalmology, University Hospital, Tobingen, Germany. METHODS: Individual computer models were constructed based on measurements, including corneal topography and axial length. The geometry of custom spherical, aspheric, toric, and toric aspheric IOLs was calculated in an optimization process with real ray tracing to provide the minimum root mean square wavefront error. The geometric optical properties in terms of residual wavefront error was simulated and approximated by Zernike polynomials. RESULTS: Data from 45 pseudophakic eyes were used to construct the models. Defocus was almost completely corrected by the spherical IOL and astigmatism, by the toric IOL. The aspheric IOL strongly reduced spherical aberration but only slightly reduced total higher-order aberrations (HOAs);both theoretical predictions corresponded to clinical investigations of wavefront measurements in pseudophakic eyes with a spherical or aspheric IOL. CONCLUSIONS: Real ray tracing calculated the exact geometry of custom IOLs to provide the minimum wavefront error, going beyond simple diopter information. Results show spherical aberration can be significantly reduced with aspheric IOLs. However, the limited possible reduction of total HOAs, even perfectly positioned custom aspheric IOLs, may be a reason for the unclear results in studies assessing the potential benefit to visual performance of currently used aspheric IOLs. J Cataract Refract Surg 2009;35:1984-1994 (C) 2009 ASCRS and ESCRS

关键词： OPHTHALMIC lenses INTRAOCULAR lenses APHAKIA EYE -- Refractive errors ray tracing algorithms BIOLOGICAL mathematical modeling ABERRATION

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Modelling and simulation of bifacial PV modules by implementing the ray tracing technique

Modelling and simulation of bifacial PV modules by implement...

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作者： Louw, Jobert Stellenbosch University

学位级别：硕士

ENGLISH ABSTRACT: This thesis shows how ray tracing can serve as an accurate irradiance mod-elling technique for bifacial PV modules. The electrical behaviour of bifacial modules is also modelled through investigation and development of two electri-cal models. Bifacial PV modules can increase the power output per unit area when compared to monofacial PV modules. This is made possible by exposing the PV cells of a bifacial module to the incident irradiance on the front and the rear side. This potential increase in power output allows bifacial PV to be an important role player in the growth of PV technology in the renewable energy market. In order to advance bifacial PV as the primary technology in the solar market, it is necessary to accurately model and simulate bifacial mod-ules. Existing bifacial PV simulation software mostly implements view factors which proves to be ineffective in accurately modelling the rear side irradiance of modules. There are some uncertainties regarding the electrical performance of bifacial PV, which can be significantly reduced once an accurate model is established for the technology. An irradiance model is developed by implementing ray tracing to model the front and rear side irradiance of bifacial modules. The irradiance model is verified by comparing modelled irradiance with irradiance measurements from an experimental bifacial PV installation. Two one-diode electrical models are implemented for bifacial modules. The two models are verified by comparing modelled power with measured power of a single bifacial module in a bifacial installation. The bifacial PV simulation software is developed by integrating the irradiance and electrical models with the python development language. After verification, the simulation software is used to simulate the effects of tilt angles, tracking, module height, albedo and row spacing on energy performance and bifacial gain of bifacial modules. A comparison is also done with existing commercial simulati

关键词： Photovoltaic power generation ray tracing algorithms Solar panels Design and construction Photovoltaic cells Design and construction UCTD

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Calculation of a wave field from ray tracing

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NUCLEAR FUSION 2010年第9期50卷 095001-095001页

作者： Cairns, R. A. Fuchs, V. Univ St Andrews Sch Math & Stat St Andrews KY16 9SS Fife Scotland Assoc EURATOM IPP AVCR Prague 18200 8 Czech Republic

Radio frequency heating and current drive are important features of many tokamaks. In order to predict the efficiency of the current drive and where it takes place in the tokamak profile, computational techniques which couple calculations of the wave field to Fokker-Planck solutions of the electron distribution function have been developed. In the electron cyclotron and lower hybrid (LH) frequency ranges the wave field is often calculated using ray tracing techniques, though more recently some full wave calculations have been done. ray tracing provides a simpler way of proceeding, but the problem arises of dealing with the situation in which there is not a single well defined beam and diffraction and beam divergence are important. Since an LH antenna produces a complicated spectrum, launching waves in a range of directions, the problem is particularly acute there. In this paper we suggest a way of calculating the wave field from tracing of multiple rays using a technique based on the stationary phase approximation. We demonstrate how it can be used and its effectiveness through a number of simple examples.

关键词： DIELECTRIC heating ELECTRIC waves FOKKER-Planck equation -- Numerical solutions ELECTRON distribution ray tracing algorithms TOKAMAKS ENERGY consumption

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GPU ray tracing

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COMMUNICATIONS OF THE ACM 2013年第5期56卷 93-101页

作者： Parker, Steven G. Friedrich, Heiko Luebke, David Morley, Keith Bigler, James Hoberock, Jared McAllister, David Robison, Austin Dietrich, Andreas Humphreys, Greg McGuire, Morgan Stich, Martin NVIDIA Santa Clara CA USA Williams Coll Williamstown MA 01267 USA

The NVIDIA (R) OptiX (TM) ray tracing engine is a programmable system designed for NVIDIA GPUs and other highly parallel architectures. The OptiX engine builds on the key observation that most ray tracing algorithms can be implemented using a small set of programmable operations. Consequently, the core of OptiX is a domain-specific just-in-time compiler that generates custom ray tracing kernels by combining user--supplied programs for ray generation, material shading, object intersection, and scene traversal. This enables the implementation of a highly diverse set of ray tracing-based algorithms and applications, including interactive rendering, offline rendering, collision detection systems, artificial intelligence queries, and scientific simulations such as sound propagation. OptiX achieves high performance through a compact object model and application of several ray tracing-specific compiler optimizations. For ease of use it exposes a single-ray programming model with full support for recursion and a dynamic dispatch mechanism similar to virtual function calls.

关键词： ray tracing GRAPHICS processing units (Computers) ray tracing algorithms COMPUTER programming RENDERING (Computer graphics) SYSTEMS design

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Large-Time-Step-Based ray-tracing Modeling of Light Delivery in One-Sidedly Cladding-Removed Step-Index Plastic Optical Fiber under Arbitrary Weave Structure

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ADVANCES IN MATERIALS SCIENCE AND ENGINEERING 2018年第1期2018卷 1-12页

作者： Moon, Sun Hee Sul, In Hwan Kumoh Natl Inst Technol Dept Mat Design Engn Gumi 39177 South Korea

An advanced theoretical method to simulate the light delivery in plastic optical fiber is presented. The final objective is to use "light" as a new media for information delivery in wearable computers. A large-time-step-based ray-tracing algorithm, which was improved from our previous research, was used to simulate the light vector movement in a complex weave structure efficiently. NURBS and free-form-deformation-based modeling was used to mimic the arbitrary weave structure. Experimentally, optical fibers were modified to control the direction of light emission. Particularly, half side of a cladding layer in the radial direction was selectively removed to enhance one-sided fabric light scattering. The cladding-removed plastic optical fiber was adopted in a textile weave structure, and its light scattering was measured quantitatively by varying the removal length, fiber curvature, and fabric weave patterns. To show the validity of the proposed simulation technique, twill structures with varying number of cross repeat numbers were used as a testbed. The unit number 2 was found to be the optimal structure for light emission, when a single POF was embedded in the textile. The proposed model showed the similar result with the actual light intensity measurement, with computation time not much than one second.

关键词： OPTICAL fibers ray tracing algorithms METAL cladding WEARABLE technology TEXTILES

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Using Monte Carlo ray tracing simulations to model the quantum harmonic oscillator modes observed in uranium nitride

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Physical Review B 2014年第14期89卷 144302-144302页

作者： J. Y. Y. Lin A. A. Aczel D. L. Abernathy S. E. Nagler W. J. L. Buyers G. E. Granroth Neutron Data Analysis and Visualization Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA

Recently an extended series of equally spaced vibrational modes was observed in uranium nitride (UN) by performing neutron spectroscopy measurements using the ARCS and SEQUOIA time-of-flight chopper spectrometers [A. A. Aczel et al., Nat. Commun. 3, 1124 (2012)]. These modes are well described by three-dimensional isotropic quantum harmonic oscillator (QHO) behavior of the nitrogen atoms, but there are additional contributions to the scattering that complicate the measured response. In an effort to better characterize the observed neutron scattering spectrum of UN, we have performed Monte Carlo ray tracing simulations of the ARCS and SEQUOIA experiments with various sample kernels, accounting for nitrogen QHO scattering, contributions that arise from the acoustic portion of the partial phonon density of states, and multiple scattering. These simulations demonstrate that the U and N motions can be treated independently, and show that multiple scattering contributes an approximate Q-independent background to the spectrum at the oscillator mode positions. Temperature-dependent studies of the lowest few oscillator modes have also been made with SEQUOIA, and our simulations indicate that the T dependence of the scattering from these modes is strongly influenced by the uranium lattice.

关键词： URANIUM MONTE Carlo method NITRIDES ray tracing algorithms HARMONIC oscillators

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