Path Tracing Research Articles

Accelerating Hair Rendering by Learning High‐Order Scattered Radiance

AbstractEfficiently and accurately rendering hair accounting for multiple scattering is a challenging open problem. Path tracing in hair takes long to converge while other techniques are either too approximate while still being computationally expensive or make assumptions about the scene. We present a technique to infer the higher order scattering in hair in constant time within the path tracing framework, while achieving better computational efficiency. Our method makes no assumptions about the scene and provides control over the renderer's bias & speedup. We achieve this by training a small multilayer perceptron (MLP) to learn the higher‐order radiance online, while rendering progresses. We describe how to robustly train this network and thoroughly analyze our resulting renderer's characteristics. We evaluate our method on various hairstyles and lighting conditions. We also compare our method against a recent learning based & a traditional real‐time hair rendering method and demonstrate better quantitative & qualitative results. Our method achieves a significant improvement in speed with respect to path tracing, achieving a run‐time reduction of 40%‐70% while only introducing a small amount of bias.

Combined volume and surface rendering with global illumination caching

We present a combined volume and surface rendering technique with global illumination caching. Our approach uses volumetric path tracing to compute the global illumination volume and local shading models for rendering the isosurface. By joining both visualization approaches, we have enhanced the display and illumination of the surfaces while preserving physically realistic illumination of the participating media. To achieve real-time performance and avoid recomputing the image when the camera view changes, we compute the global illumination volume incrementally and defer the projection to a later step. We evaluated our technique by comparing different local shading models for isosurface rendering with the result of full volumetric path tracing and with the non-caching variant of our technique. Results show that the caching and non-caching variants perform comparably well, while the caching variant has the added benefit of being camera-view-independent. Additionally, we show that our approach emphasizes the surfaces within volumes better than volumetric path tracing.

Spatially eutrophication potential and policy implication of nitrogen emission for surface water: A case study in Guangzhou city, China

Understanding the spatial distribution and path tracing of eutrophication caused by nitrogen (N) enrichment in urban freshwater is crucial for whole-process and precise damage effect control. This study constructed a site-specific life cycle impact assessment (LCIA) model, covering the overall cause–effect chain from source emission to endpoint effect, to assess N-induced eutrophication potential at the species damage level. Applied to Guangzhou city, China, marked spatial disparities in eutrophication potential were derived, with higher values in the downtown areas driven by anthropogenic disturbances, such as wastewater discharge. Spatially differentiated measures were provided through eutrophication hotspot identification and driver tracking. This study offers a necessary complement for eutrophication impact category indicators in LCIA methodology and lays a scientific foundation for potential hotpots diagnosis and targeted mitigation policy-making.

Improving Accuracy of Real-Time Positioning and Path Tracking by Using an Error Compensation Algorithm against Walking Modes.

Wide-range application scenarios, such as industrial, medical, rescue, etc., are in various demand for human spatial positioning technology. However, the existing MEMS-based sensor positioning methods have many problems, such as large accuracy errors, poor real-time performance and a single scene. We focused on improving the accuracy of IMU-based both feet localization and path tracing, and analyzed three traditional methods. In this paper, a planar spatial human positioning method based on high-resolution pressure insoles and IMU sensors was improved, and a real-time position compensation method for walking modes was proposed. To validate the improved method, we added two high-resolution pressure insoles to our self-developed motion capture system with a wireless sensor network (WSN) system consisting of 12 IMUs. By multi-sensor data fusion, we implemented dynamic recognition and automatic matching of compensation values for five walking modes, with real-time spatial-position calculation of the touchdown foot, enhancing the 3D accuracy of its practical positioning. Finally, we compared the proposed algorithm with three old methods by statistical analysis of multiple sets of experimental data. The experimental results show that this method has higher positioning accuracy in real-time indoor positioning and path-tracking tasks. The methodology can have more extensive and effective applications in the future.

3D Reconstruction of Celadon from a 2D Image: Application to Path Tracing and VR

We present a straightforward approach for reconstructing 3D celadon models from a single 2D image. The celadon is a historical example of the surface of revolution. Our approach uses a surface of revolution technique to generate the basic shape of the celadon and then applies texture mapping to create a realistic appearance. The process involves detecting the contour and corners of the celadon image, determining an axis of revolution, generating a profile curve, and finally constructing a 3D celadon model. Additionally, we create models as triangular meshes at multiple resolutions, employing a B-spline curve as the profile curve. It enhances the adaptability of the models for various purposes. We render various scenes using a path tracer to assess the suitability of the generated 3D celadon models and generate a VR celadon museum with the models. Overall, our approach offers a simple and efficient solution for reconstructing a 3D celadon model, generating VR content, and demonstrating extensive applicability across numerous disciplines.

Spatiotemporally Consistent HDR Indoor Lighting Estimation

We propose a physically motivated deep learning framework to solve a general version of the challenging indoor lighting estimation problem. Given a single LDR image with a depth map, our method predicts spatially consistent lighting at any given image position. Particularly, when the input is an LDR video sequence, our framework not only progressively refines the lighting prediction as it sees more regions, but also preserves temporal consistency by keeping the refinement smooth. Our framework reconstructs a spherical Gaussian lighting volume (SGLV) through a tailored 3D encoder-decoder, which enables spatially consistent lighting prediction through volume ray tracing, a hybrid blending network for detailed environment maps, an in-network Monte Carlo rendering layer to enhance photorealism for virtual object insertion, and recurrent neural networks (RNN) to achieve temporally consistent lighting prediction with a video sequence as the input. For training, we significantly enhance the OpenRooms public dataset of photorealistic synthetic indoor scenes with around 360k HDR environment maps of much higher resolution and 38k video sequences, rendered with GPU-based path tracing. Experiments show that our framework achieves lighting prediction with higher quality compared to state-of-the-art single-image or video-based methods, leading to photorealistic AR applications such as object insertion.

Near Real-Time 3D Path Visualization for Navigation Systems with IMU Sensor and Kalman Filter

Path tracing or simulation in robotics Operating System ROS is very popular in highly dynamic research projects. The Matplotlib’s 3D path tracing is a graphical 3-axis plotting tool with real- time data visualization over a very long range. The data’s are generated in all 3 dimensions from accelerometer readings for visualizing the ground station navigation system. The communication between the two radio modules are established and the data’s are transmitted between the two modules that are placed remotely. The data can be plotted in real-time in 3 Dimensions and then, visualized. The main goal of path tracing is to make a comparative study between 3 axis displacement as any kind of irregular plot or trace can be a sign of a dangerous situations that can occur. There are many other significances of this concept that can be used in navigation systems.

Evolution Characteristics of DC Breakdown for Biaxially Oriented Polypropylene Films

Biaxially oriented polypropylene (BOPP) films are the preferred storage dielectric for dry-type film capacitors due to excellent dielectric properties. However, the evolution characteristics of DC Breakdown of BOPP film in air remain unclear. This study focuses on the influence of curvature, contact area and material of electrode on the DC breakdown in BOPP films. The on-line/off-line measurements of surface potential and characterizations of trap distribution are achieved. And the simulations of surface charge, electric field and energy injection are accomplished. The breakdown path and degradation traces in BOPP films are also analyzed. The experimental results show that the effective insulation distance is the key to determine the actual performance of the film, affected by the trap distribution and density. This paper has a reference for the optimization of insulation structure for dry-type film capacitors in the field of high-voltage direct current (HVDC).

Efficient Specular Glints Rendering With Differentiable Regularization.

Rendering glinty details from specular microstructure enhances the level of realism in computer graphics. However, naive sampling fails to render such effects, due to insufficient sampling of the contributing normals on the surface patch visible through a pixel. Other approaches resort to searching for the relevant normals in more explicit ways, but they rely on special acceleration structures, leading to increased storage costs and complexity. In this article, we propose to render specular glints through a different method: differentiable regularization. Our method includes two steps: first, we use differentiable path tracing to render a scene with a larger light size and/or rougher surfaces and record the gradients with respect to light size and roughness. Next, we use the result for the larger light size and rougher surfaces, together with their gradients, to predict the target value for the required light size and roughness by extrapolation. In the end, we get significantly reduced noise compared to rendering the scene directly. Our results are close to the reference, which uses many more samples per pixel, although our method cannot guarantee unbiased convergence to the reference. The overhead for differentiable rendering and prediction is small, so our improvement is almost free. We demonstrate our differentiable regularization on several normal maps, all of which benefit from the method.

Memory‐Efficient GPU Volume Path Tracing of AMR Data Using the Dual Mesh

AbstractA common way to render cell‐centric adaptive mesh refinement (AMR) data is to compute the dual mesh and visualize that with a standard unstructured element renderer. While the dual mesh provides a high‐quality interpolator, the memory requirements of the dual mesh data structure are significantly higher than those of the original grid, which prevents rendering very large data sets. We introduce a GPU‐friendly data structure and a clustering algorithm that allow for efficient AMR dual mesh rendering with a competitive memory footprint. Fundamentally, any off‐the‐shelf unstructured element renderer running on GPUs could be extended to support our data structure just by adding a gridlet element type in addition to the standard tetrahedra, pyramids, wedges, and hexahedra supported by default. We integrated the data structure into a volumetric path tracer to compare it to various state‐of‐the‐art unstructured element sampling methods. We show that our data structure easily competes with these methods in terms of rendering performance, but is much more memory‐efficient.

Analysis of Forward Kinematics of 2R Robotic Arm

In Kinematics, the analysis of acceleration and velocity is usually done whereas the forces are neglected. The machine’s smallest unit is the link, which is akin to a cell in the human body. Robotics is built on the foundation of machines. A pair is established by the combination of links which leads to the construction of linkage. A mechanical linkage is a collection of bodies that are connected to control forces and movement. The combination of linkage (also known as Mechanism) generates Machine. The robot’s kinematics equations are used in robotics, video games and animation. Inverse kinematics is the mathematical process of determining variable joint parameters necessary to place an object at the end of a kinematic chain in a specific position and orientation with respect to the start of the chain, such as robot manipulator or skeleton of an animated character. The role of Forward and Inverse Kinematics in a 2R Robotic Arm are studied with successful demonstrations. Forward Kinematics of a 2R Robotic Arm using Matlab and Python confirming similar results are exhibited (Figure 8 and Figure 9). Matlab illustrated 2D Path Tracing for 2R Robotic Arm with Inverse Kinematics. Finally, inverse kinematics of 2R Robotic Arm in Matlab using fuzzy logic is modelled successfully. Thus, it helps in the understanding of kinematics and can be used in the simulation of machines.

The contribution of industrial emissions to ozone pollution: identified using ozone formation path tracing approach

Wintertime meteorological conditions are usually unfavorable for ozone (O3) formation due to weak solar irradiation and low temperature. Here, we observed a prominent wintertime O3 pollution event in Shijiazhuang (SJZ) during the Chinese New Year (CNY) in 2021. Meteorological results found that the sudden change in the air pressure field, leading to the wind changing from northwest before CNY to southwest during CNY, promotes the accumulation of air pollutants from southwest neighbor areas of SJZ and greatly inhibits the diffusion and dilution of local pollutants. The photochemical regime of O3 formation is limited by volatile organic compounds (VOCs), suggesting that VOCs play an important role in O3 formation. With the developed O3 formation path tracing (OFPT) approach for O3 source apportionment, it has been found that highly reactive species, such as ethene, propene, toluene, and xylene, are key contributors to O3 production, resulting in the mean O3 production rate (PO3) during CNY being 3.7 times higher than that before and after CNY. Industrial combustion has been identified as the largest source of the PO3 (2.6 ± 2.2 ppbv h−1), with the biggest increment (4.8 times) during CNY compared to the periods before and after CNY. Strict control measures in the industry should be implemented for O3 pollution control in SJZ. Our results also demonstrate that the OFPT approach, which accounts for the dynamic variations of atmospheric composition and meteorological conditions, is effective for O3 source apportionment and can also well capture the O3 production capacity of different sources compared with the maximum incremental reactivity (MIR) method.

Nitrogen Surplus Displays a Spurious Environmental Kuznets Curve in Germany

We examine the relationship between nitrogen surplus per hectare and the median monthly wage per capita considering the Environmental Kuznets Curve (EKC) theory. The EKC hypothesizes an inverse U-shape relationship between environmental pollution and per capita income. We use a novel panel data set for nitrogen surplus as an environmental pollutant and a measure of the median monthly wage per capita during the period from 1999 to 2018 for 401 counties in Germany. Our estimation results show that nitrogen surplus displays a spurious EKC in Germany. It is spurious because the inverse U-shape relationship of nitrogen surplus and median wage is rejected by almost all model specifications and by tracing of individual county paths. This implies that in Germany economic growth has not cleaned up the environmental damage from nitrogen surplus. The affected counties remain in a spatial cluster (shown with the individual county paths) that they cannot break out of in the course of the EKC, at least not without political intervention.

Efficient Hardware Acceleration of Robust Volumetric Light Transport Simulation

AbstractEfficiently simulating the full range of light effects in arbitrary input scenes that contain participating media is a difficult task. Unified points, beams and paths (UPBP) is an algorithm capable of capturing a wide range of media effects, by combining bidirectional path tracing (BPT) and photon density estimation (PDE) with multiple importance sampling (MIS). A computationally expensive task of UPBP is the MIS weight computation, performed each time a light path is formed. We derive an efficient algorithm to compute the MIS weights for UPBP, which improves over previous work by eliminating the need to iterate over the path vertices. We achieve this by maintaining recursive quantities as subpaths are generated, from which the subpath weights can be computed. In this way, the full path weight can be computed by only using the data cached at the two vertices at the ends of the subpaths. Furthermore, a costly part of PDE is the search for nearby photon points and beams. Previous work has shown that a spatial data structure for photon mapping can be implemented using the hardware‐accelerated bounding volume hierarchy of NVIDIA's RTX GPUs. We show that the same technique can be applied to different types of volumetric PDE and compare the performance of these data structures with the state of the art. Finally, using our new algorithm and data structures we fully implement UPBP on the GPU which we, to the best of our knowledge, are the first to do so.

Survey on NLOS Identification and Error Mitigation for UWB Indoor Positioning

Ultra-wideband (UWB) positioning systems often operate in a non-line-of-sight (NLOS) environment. NLOS propagation has become the main source of ultra-wideband indoor positioning errors. As such, how to identify and correct NLOS errors has become a key problem that must be solved in high-accuracy indoor positioning technology. This paper firstly describes the influence of the NLOS propagation path on localization accuracy and the generation method of ultra-wideband signals, and secondly classifies and analyzes the currently available algorithms for ultra-wideband non-line-of-sight (NLOS) identification and error suppression. For the identification of NLOS, the residual analysis judgement method, statistical feature class identification method, machine learning method and geometric feature judgement method are discussed. For the suppression of NLOS propagation errors, weighting-based methods, filtering-based methods, line-of-sight reconstruction algorithms, neural network algorithms, optimization methods with constraints, and path tracing methods are discussed. Finally, we conclude the paper and point out the problems that need to be solved in NLOS indoor positioning.

Bi-directional Monte-Carlo modelling of solar-induced chlorophyll fluorescence images for 3D vegetation canopies in the DART model

Remote sensing (RS) of solar-induced chlorophyll fluorescence (SIF) has a great potential for monitoring plant photosynthetic activity. Radiative transfer models (RTM) are essential to better interpret and extract information from SIF signals. DART is one of the most comprehensive and accurate 3D RTMs. Its standard mode DART-FT simulates SIF using a discrete ordinates method but is not adapted to large landscapes due to computational constraints. DART-Lux, the new mode based on a bi-directional path tracing algorithm, greatly improves DART computational efficiency for simulating images. This paper presents the theory of a novel SIF modelling algorithm in DART-Lux. We verified its accuracy with DART-FT and the SCOPE model for three types of canopies: turbid medium, maize field and forest. DART-Lux closely matches DART-FT (relative difference < 2%) with much better computational efficiency depending on the scene complexity, number of spectral bands and needed accuracy. For example, simulation time is reduced by a factor of ≈48, and memory usage by ≈50 for a maize field at 1 cm resolution. It allowed to simulate SIF images of large scenes as the 3×3km2 Ripperdan agricultural site that DART-FT could not simulate. The new SIF modelling algorithm opens new horizons for RS studies of large and complex landscapes. It is available as part of released DART versions (v1152 onwards) (https://dart.omp.eu/).

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.

Path Tracing vs. Volume Rendering Technique in Post-Surgical Assessment of Bone Flap in Oncologic Head and Neck Reconstructive Surgery: A Preliminary Study.

This study aims to compare a relatively novel three-dimensional rendering called Path Tracing (PT) to the Volume Rendering technique (VR) in the post-surgical assessment of head and neck oncologic surgery followed by bone flap reconstruction. This retrospective study included 39 oncologic patients who underwent head and neck surgery with free bone flap reconstructions. All exams were acquired using a 64 Multi-Detector CT (MDCT). PT and VR images were created on a dedicated workstation. Five readers, with different expertise in bone flap reconstructive surgery, independently reviewed the images (two radiologists, one head and neck surgeon and two otorhinolaryngologists, respectively). Every observer evaluated the images according to a 5-point Likert scale. The parameters assessed were image quality, anatomical accuracy, bone flap evaluation, and metal artefact. Mean and median values for all the parameters across the observer were calculated. The scores of both reconstruction methods were compared using a Wilcoxon matched-pairs signed rank test. Inter-reader agreement was calculated using Spearman's rank correlation coefficient. PT was considered significantly superior to VR 3D reconstructions by all readers (p < 0.05). Inter-reader agreement was moderate to strong across four out of five readers. The agreement was stronger with PT images compared to VR images. In conclusion, PT reconstructions are significantly better than VR ones. Although they did not modify patient outcomes, they may improve the post-surgical evaluation of bone-free flap reconstructions following major head and neck surgery.

Light subpath reservoir for interactive ray-traced global illumination

In this paper, we propose a novel approach for sampling indirect illumination based on bidirectional path tracing and world space resampling reservoir. We cache light subpaths with high contribution in a world space grid, allowing for sampling at arbitrary vertices along the eye path. In order to find optimal samples, we continuously update the reservoirs stored in each cell according to the resampling principles. Experiments have shown that our algorithm achieves noticeable noise reduction in scenes lit by indirect light compared with path tracing, at the cost of additional time and memory consumption, while still maintaining interactive frame rates. In some special cases, our method even shows better results than a plain bidirectional path tracer, in terms of both image quality and performance.

The design and validation of a rain model for a simulated automotive environment

This paper presents the design of an accurate rain model for the commercially-available Anyverse automotive simulation environment. The model incorporates the physical properties of rain and a process to validate the model against real rain is proposed. Due to the high computational complexity of path tracing through a particle-based model, a second more computationally efficient model is also proposed. For the second model, the rain is modeled using a combination of a particle-based model and an attenuation field. The attenuation field is fine-tuned against the particle-only model to minimize the difference between the models.