Path Tracing Technique Research Articles

Photorealistic Rapid Computer-Generated Holography Employing an Enhanced Path Tracing Technique With Sequence Generated Trial

Photorealistic Rapid Computer-Generated Holography Employing an Enhanced Path Tracing Technique With Sequence Generated Trial

Tracing curvature paths on trimmed multipatch surfaces

Advances in architectural geometry and computation have created strategies to rationalize complex building envelopes. This paper presents techniques to identify paths on freeform surfaces by prescribing specific curvature properties. The paths can be defined by the normal curvature or the geodesic torsion. In special cases, asymptotic and principal curvature lines can be determined. Such paths are used for the design of gridshells with lamellar elements. A brief introduction to differential geometry of freeform surfaces provides the relevant foundations for the method. The relevant quantities and relations are highlighted with illustrations. The consistent description of the paths in the parameter space of the surface avoids unnecessary and complex projection operations. This allows a computationally efficient and robust implementation. The tracing is explained for the simple case of a single surface and extended to trimmed multipatches which are used for geometric modeling in common computer-aided design (CAD) programs. The topological structure of the multipatch was used to trace paths across several surfaces. To enable interactive design, the path tracing techniques were integrated into the parametric CAD package Grasshopper for Rhino. Additional components for curvature analysis were implemented to analyze and evaluate designs. To simplify the handling of curvature lines, a geometry type for embedded curves was introduced and implemented within a CAD environment. Finally, the use of these tools for the design of architecturally sophisticated gridshells is presented along with three projects of increasing complexity.

On the nonlinear post-critical responses of VAT sandwich beams with variable stiffness composite skins under axial compression

In this article, the nonlinear post-critical problem of Variable Angle Tow (VAT) sandwich beams with variable stiffness composite skins under axial compression is studied for the first time. The present sandwich beam model is constructed from a modified version of extended high-order sandwich panel theory (EHSAPT), in which the first-order shear deformation theory with von Kármán’s strain–displacement relation is utilized for the skin layer, whereas the high-order theory with linear strain–displacement is applied to characterize the deformation of the core layer. Based on the principal of virtual work, a system of differential equations with variable coefficients is firstly formulated for the postbuckling problem of VAT sandwich beams with variable stiffness composite skins under plane-strain state. Meanwhile, a more efficient Rayleigh–Ritz approach combined with variational formulas is employed to derive the nonlinear algebraic equations in weak forms, and thereafter a sophisticated path-tracing technique is applied to determine the postbuckling equilibrium path. Both super-critical and sub-critical postbuckling states of VAT sandwich beams can be readily captured under the present analytical model framework. The accuracy and effectiveness of the developed Rayleigh–Ritz procedure are validated by comparing against the results available in literature. Effects of variation in skin stiffness on both the critical instability and post-critical behaviours of VAT sandwich beams are discussed in numerical examples. It is found that the change in skin stiffness plays a determinative role in the formation of nonperiodic wrinkling patterns of VAT sandwich beams. In addition, the change in skin stiffness may cause global and local instability loads to be close to each other, and accordingly, the possibility of encountering interactive buckling is increased. The results presented herein may be beneficial for the design of VAT sandwich structures under compression.

Once‐more scattered next event estimation for volume rendering

AbstractWe present a Monte Carlo path tracing technique to sample extended next event estimation contributions in participating media: we consider one additional scattering vertex on the way to the next event, accounting for focused blur, resulting in visually interesting image features. Our technique is tailored to thin homogeneous media with strongly forward scattering phase functions, such as water or atmospheric haze. Previous methods put emphasis on sampling transmittances or geometric factors, and are either limited to isotropic scattering, or used tabulation or polynomial approximation to account for some specific phase functions. We will show how to jointly importance sample the product of an arbitrary phase function with analytic sampling in the solid angle domain and the two reciprocal squared distance terms of the adjacent edges of the transport path. The technique is fast and simple to implement in an existing rendering system. Our estimator is designed specifically for forward scattering, so the new technique has to be combined with other estimators to cover the backward scattering contributions.

Real-Time Rendering of Point Clouds With Photorealistic Effects: A Survey

Readily available RGB-D cameras in smart phones and improving 3D scanning technologies have made it possible to produce detailed point cloud and point-based models of real world objects even in real time. Rendering such models in high quality and at satisfactory frame rates is needed for realistic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">extended reality</i> (XR) applications. This publication reviews real-time photorealistic point cloud rendering methods which directly ray trace or rasterize point cloud models, with an emphasis on ray tracing and real-time performance. We found that real-time direct point cloud ray tracing research has been focused on static non-animated content, and thus, open research possibilities include adapting modern dedicated ray tracing hardware for increased performance for animated and live captured scenes, and adding path tracing techniques to increase photorealistic effects in the rendering result. A categorization and discussion on the capabilities of state-of-the-art photorealistic point cloud rendering methods is presented by surveying both real-time and offline methods, which are assumed to become real-time capable with the advances in near-future hardware. Challenges and future trends are derived by comparing different rasterization and ray tracing methods as well as acceleration structures for point clouds in terms of produced rendering effects and speed.

Adaptive Temporal Sampling for Volumetric Path Tracing of Medical Data

AbstractMonte‐Carlo path tracing techniques can generate stunning visualizations of medical volumetric data. In a clinical context, such renderings turned out to be valuable for communication, education, and diagnosis. Because a large number of computationally expensive lighting samples is required to converge to a smooth result, progressive rendering is the only option for interactive settings: Low‐sampled, noisy images are shown while the user explores the data, and as soon as the camera is at rest the view is progressively refined. During interaction, the visual quality is low, which strongly impedes the user's experience. Even worse, when a data set is explored in virtual reality, the camera is never at rest, leading to constantly low image quality and strong flickering. In this work we present an approach to bring volumetric Monte‐Carlo path tracing to the interactive domain by reusing samples over time. To this end, we transfer the idea of temporal antialiasing from surface rendering to volume rendering. We show how to reproject volumetric ray samples even though they cannot be pinned to a particular 3D position, present an improved weighting scheme that makes longer history trails possible, and define an error accumulation method that downweights less appropriate older samples. Furthermore, we exploit reprojection information to adaptively determine the number of newly generated path tracing samples for each individual pixel. Our approach is designed for static, medical data with both volumetric and surface‐like structures. It achieves good‐quality volumetric Monte‐Carlo renderings with only little noise, and is also usable in a VR context.

Low overhead path regeneration

Monte Carlo Path Tracing is a core light transport technique which is used for modern methods (like BDPT, MLT, VCM and others). One of the main challenge of efficient GPU Path Tracing implementation is inefficient workload caused by paths of different lengths; few threads process the long paths, while other threads are idle. A work distribution technique called "Path Regeneration" is commonly used to solve this problem. We introduce a novel GPU implementation of path regeneration technique called "in place block based path regeneration." In comparison to previous approaches our algorithm possesses two main advantages: it has lower self-cost and it does not move any per-ray data along threads in memory, thus, our algorithm can be easily integrated to any advanced path tracing technique (like BDPT, MLT and other) or photon mapping. We tested our solution with path tracing using both CUDA and OpenCL.

The complete bifurcation structure of nonlinear boundary problem for cylindrical panel subjected to uniform external pressure

The present paper presents the complete bifurcation structure of nonlinear boundary problem of thin-walled systems for cylindrical panel subjected to uniform external pressure. We examine various boundary conditions on straight edges (free, simply supported, rigidly clamped edges, edges with prescribed fixed joint conditions); curvilinear edges are simply supported. To construct solutions of the boundary problem in question and to trace equilibrium paths, we employ the non-linear extended Kantorovich method in conjunction with a conventional path-tracing technique. The structure has bifurcation paths associated with symmetric, skew-symmetric, asymmetric, and snap-through deformed shapes that provides a basis for analysis of the worst shape imperfections.

Hierarchical Program Paths

Complete dynamic control flow is a fundamental kind of execution profile about program executions with a wide range of applications. Tracing the dynamic control flow of program executions for a brief period easily generates a trace consisting of billions of control flow events. The number of events in such a trace is large, making both path tracing and path querying to incur significant slowdowns. A major class of path tracing techniques is to design novel trace representations that can be generated efficiently, and encode the inputted sequences of such events so that the inputted sequences are still derivable from the encoded and smaller representations. The control flow semantics in such representations have, however, become obscure, which makes implementing path queries on such a representation inefficient and the design of such queries complicated. We propose a novel two-phase path tracing framework— Hierarchical Program Path (HPP)—to model the complete dynamic control flow of an arbitrary number of executions of a program. In Phase 1, HPP monitors each execution, and efficiently generates a stream of events, namely HPPTree, representing a novel tree-based representation of control flow for each thread of control in the execution. In Phase 2, given a set of such event streams, HPP identifies all the equivalent instances of the same exercised interprocedural path in all the corresponding HPPTree instances, and represents each such equivalent set of paths with a single subgraph, resulting in our compositional graph-based trace representation, namely, HPPDAG. Thus, an HPPDAG instance has the potential to be significantly smaller in size than the corresponding HPPTree instances, and still completely preserves the control flow semantics of the traced executions. Control flow queries over all the traced executions can also be directly performed on the single HPPDAG instance instead of separately processing the trace representation of each execution followed by aggregating their results. We validate HPP using the SPLASH2 and SPECint 2006 benchmarks. Compared to the existing technique, named BLPT (Ball-Larus-based Path Tracing), HPP generates significantly smaller trace representations and incurs fewer slowdowns to the native executions in online tracing of Phase 1. The HPPDAG instances generated in Phase 2 are significantly smaller than their corresponding BLPT and HPPTree traces. We show that HPPDAG supports efficient backtrace querying, which is a representative path query based on complete control flow trace. Finally, we illustrate the ease of use of HPPDAG by building a novel and highly efficient path profiling technique to demonstrate the applicability of HPPDAG.

Fast quantum communication in linear networks

Here we consider the speed at which quantum information can be transferred between the nodes of a linear network. Because such nodes are linear oscillators, this speed is also important in the cooling and state preparation of mechanical oscillators, as well as in frequency conversion. We show that if there is no restriction on the size of the linear coupling between two oscillators, then there exist control protocols that will swap their respective states with high fidelity within a time much shorter than a single oscillation period. Standard gradient search methods fail to find these fast protocols. We were able to do so by augmenting standard search methods with a path-tracing technique, demonstrating that this technique has remarkable power to solve time-optimal control problems, as well as confirming the highly challenging nature of these problems. As a further demonstration of the power of path tracing, first introduced by Moore Tibbets et al. (Phys. Rev. A, 86 (2012) 062309), we apply it to the generation of entanglement in a linear network.

High-order diffraction and diffuse reflections for interactive sound propagation in large environments

We present novel algorithms for modeling interactive diffuse reflections and higher-order diffraction in large-scale virtual environments. Our formulation is based on ray-based sound propagation and is directly applicable to complex geometric datasets. We use an incremental approach that combines radiosity and path tracing techniques to iteratively compute diffuse reflections. We also present algorithms for wavelength-dependent simplification and visibility graph computation to accelerate higher-order diffraction at runtime. The overall system can generate plausible sound effects at interactive rates in large, dynamic scenes that have multiple sound sources. We highlight the performance in complex indoor and outdoor environments and observe an order of magnitude performance improvement over previous methods.

Nonlinear behavior and buckling of cylindrical shells subjected to localized external pressure

Buckling loads and postbuckling behavior of cylindrical shells subjected to localized external pressure are considered. The modified extended Kantorovich method with path-tracing technique is applied to determine the buckling loads of the cylindrical shells. It is found that the load is dependent nonmonotonically on geometrical parameters of the area subjected to external pressure. Respective postbuckling shapes show correlation with the shapes corresponding to secondary bifurcation paths for the cases of a cylindrical shell under uniform external pressure and a cylindrical shell under uniform axial load.

Computer-aided process dimensioning

Conventionally, working dimensions have to be given before the construction of a tolerance chart can begin. Because the method of determining the working dimensions is based on trial and error, it is tedious and time-consuming. This paper proposes a method that can generate the working dimensions automatically from the process sequences and the blueprint dimensions. The method uses a relationship matrix to represent the process sequences and a special path-tracing technique to identify the process links. A unique algorithm is developed to reduce the unknown working dimensions to a system of linear equations, which is then solved using the Gauss elimination technique. This method can either be adopted by the process planner or implemented on a microcomputer. With this method, different processing sequences based on different factors, e.g. cost, machining time, etc., can be evaluated efficiently and economically. The developed program is then tested on a practical example.

A complete tolerance charting system

Abstract Manual computation of tolerance charts is both tedious and time-consuming. This paper presents an efficient method of automatically determining the working dimensions and their balanced tolerances. With this method, the feasibility of different process plans can be evaluated efficiently and economically. A unique algorithm, based on a special path tracing technique, is developed to reduce the unknown working dimensions to a system of linear equations. The Gauss elimination technique is then employed to solve for the working dimensions. The tolerance balancing process is accomplished using a separate mathematical model. The complete system, comprising the tolerance charting and optimization modules, is finally tested on an example.

A novel critical path heuristic for fast fault grading

A novel fault grading heuristic is presented, based on the critical path tracing technique that tackles the problems associated with fan-out reconverging nodes (FORNs) without using forward propagation of the fault effects. To determine the criticality status of a fan-out reconverging node, which can differ from that of its fan-out branches (FOBs), the concepts of evidencing and masking paths are used. Using the statistics from exact fault simulations, heuristic rules are derived for the generation of masking and evidencing paths. The results obtained on benchmark circuits show good accuracy for fault coverage estimates and a computation time linear in the number of gates and comparable to that of the fault-free simulation. >

Functional specification and testing of logic circuits

The very rapid growth in the complexity of testing logic circuits presents a description problem of increasing severity. In this paper two approaches to this problem are discussed and compared. In the first approach path-tracing techniques are used to generate the experiment description of logic circuits from their binary decision diagram representation. In the second approach symbolic execution is used to provide a link between the functional description of a logic circuit, written in a procedural language, and its nonprocedural assertion description. A commercial logic circuit is used throughout the paper as a running example.

Test Sets for Combinational Logic—The Edge-Tracing Approach

A method for fault analysis of multilevel combinational logic circuits with single stuck-at-faults is described. It determines the sensitizing input combinations (separating edges) from the output function and then traces their paths from the output toward the inputs. The handling of multiple path sensitization in this approach is much simpler than in other path-tracing techniques. Subscripting of variables is not needed and dead-ending (as encountered in the D-algorithm) cannot occur.