Interactive Ray Tracing Research Articles

Hybrid Rendering for Interactive Visualization of Mantle Convection.

In this article, we describe our system for visualizing convection in the Earth's mantle using hybrid rendering-a combination of interactive raytracing, raycasting, and conventional rasterization graphics. The dataset for the SciVis 2021 contest includes a velocity vector field and multiple scalar fields, such as temperature and thermal conductivity anomalies, which we display using isosurface raycasting, streamlines, and line integral convolution, among other techniques. We demonstrate how these methods can be used to explore the dataset, identify slabs, plumes, and stagnations, and detect the influence of 660-km depth endothermic phase transition and mid-mantle spin transition on the mantle dynamics.

Interactive Monte Carlo denoising using affinity of neural features

High-quality denoising of Monte Carlo low-sample renderings remains a critical challenge for practical interactive ray tracing. We present a new learning-based denoiser that achieves state-of-the-art quality and runs at interactive rates. Our model processes individual path-traced samples with a lightweight neural network to extract per-pixel feature vectors. The rest of our pipeline operates in pixel space. We define a novel pairwise affinity over the features in a pixel neighborhood, from which we assemble dilated spatial kernels to filter the noisy radiance. Our denoiser is temporally stable thanks to two mechanisms. First, we keep a running average of the noisy radiance and intermediate features, using a per-pixel recursive filter with learned weights. Second, we use a small temporal kernel based on the pairwise affinity between features of consecutive frames. Our experiments show our new affinities lead to higher quality outputs than techniques with comparable computational costs, and better high-frequency details than kernel-predicting approaches. Our model matches or outperfoms state-of-the-art offline denoisers in the low-sample count regime (2--8 samples per pixel), and runs at interactive frame rates at 1080p resolution.

Diffraction Kernels for Interactive Sound Propagation in Dynamic Environments.

We present a novel method to generate plausible diffraction effects for interactive sound propagation in dynamic scenes. Our approach precomputes a diffraction kernel for each dynamic object in the scene and combines them with interactive ray tracing algorithms at runtime. A diffraction kernel encapsulates the sound interaction behavior of individual objects in the free field and we present a new source placement algorithm to significantly accelerate the precomputation. Our overall propagation algorithm can handle highly-tessellated or smooth objects undergoing rigid motion. We have evaluated our algorithm's performance on different scenarios with multiple moving objects and demonstrate the benefits over prior interactive geometric sound propagation methods. We also performed a user study to evaluate the perceived smoothness of the diffracted field and found that the auditory perception using our approach is comparable to that of a wave-based sound propagation method.

A Ray Tracing Simulation of Sound Diffraction Based on the Analytic Secondary Source Model

This paper describes a novel ray tracing method for solving sound diffraction problems. This method is a Monte Carlo solution to the multiple integration in the analytic secondary source model of edge diffraction; it uses ray tracing to calculate sample values of the integrand. The similarity between our method and general ray tracing makes it possible to utilize the various approaches developed for ray tracing. Our implementation employs the OptiX ray tracing engine, which exhibits good acceleration performance on a graphics processor. Two importance sampling methods are derived from different aspects, and they provide an efficient and accurate way to solve the numerically challenging integration. The accuracy of our method was demonstrated by comparing its estimates with the ones calculated by reference software. An analysis of signal-to-noise ratios using an auditory filter bank was performed objectively and subjectively in order to evaluate the error characteristics and perceptual quality. The applicability of our method was evaluated with a prototype system of interactive ray tracing.

From microscopy data to in silico environments for in vivo-oriented simulations

In our previous study, we introduced a combination methodology of Fluorescence Correlation Spectroscopy (FCS) and Transmission Electron Microscopy (TEM), which is powerful to investigate the effect of intracellular environment to biochemical reaction processes. Now, we developed a reconstruction method of realistic simulation spaces based on our TEM images. Interactive raytracing visualization of this space allows the perception of the overall 3D structure, which is not directly accessible from 2D TEM images. Simulation results show that the diffusion in such generated structures strongly depends on image post-processing. Frayed structures corresponding to noisy images hinder the diffusion much stronger than smooth surfaces from denoised images. This means that the correct identification of noise or structure is significant to reconstruct appropriate reaction environment in silico in order to estimate realistic behaviors of reactants in vivo. Static structures lead to anomalous diffusion due to the partial confinement. In contrast, mobile crowding agents do not lead to anomalous diffusion at moderate crowding levels. By varying the mobility of these non-reactive obstacles (NRO), we estimated the relationship between NRO diffusion coefficient (Dnro) and the anomaly in the tracer diffusion (α). For Dnro=21.96 to 44.49 μm2/s, the simulation results match the anomaly obtained from FCS measurements. This range of the diffusion coefficient from simulations is compatible with the range of the diffusion coefficient of structural proteins in the cytoplasm. In addition, we investigated the relationship between the radius of NRO and anomalous diffusion coefficient of tracers by the comparison between different simulations. The radius of NRO has to be 58 nm when the polymer moves with the same diffusion speed as a reactant, which is close to the radius of functional protein complexes in a cell.

Interactive sound propagation using compact acoustic transfer operators

We present an interactive sound propagation algorithm that can compute high orders of specular and diffuse reflections as well as edge diffractions in response to moving sound sources and a moving listener. Our formulation is based on a precomputed acoustic transfer operator, which we compactly represent using the Karhunen-Loeve transform. At runtime, we use a two-pass approach that combines acoustic radiance transfer with interactive ray tracing to compute early reflections as well as higher-order reflections and late reverberation. The overall approach allows accuracy to be traded off for improved performance at runtime, and has a low memory overhead. We demonstrate the performance of our algorithm on different scenarios, including an integration of our algorithm with Valve's Source game engine.

Razor

Recent work demonstrates that interactive ray tracing is possible on desktop systems, but there is still much debate as to how to most efficiently support advanced visual effects such as soft shadows, smooth freeform surfaces, complex shading, and animated scenes. With these challenges in mind, we reconsider the options for designing a rendering system and present Razor , a new software rendering architecture for distribution ray tracing designed to produce high-quality images with high performance on future single-chip many-core hardware. Razor includes two noteworthy capabilities: a set of techniques for quickly building the kd-tree acceleration structure on demand every frame from a scene graph and a system design that allows for crack-free multiresolution geometry with each ray independently choosing its geometry resolution. Razor's per-frame kd-tree build is designed to robustly handle arbitrarily scene animation, while its per-ray multiresolution geometry provides continuous level of detail driven by ray and path differentials. Razor also decouples shading from visibility computations using a two-phase shading scheme inspired by the REYES system, and caches tessellated representations of freeform surfaces at multiple levels of detail. We present experimental results gathered from a prototype system implemented on eight CPU cores, and discuss which aspects of the system are most successful and which would benefit from further investigation.

Comments on: Palmer, D., 2010. Is visual interactive ray trace an efficacious strategy for refraction inversion? Exploration Geophysics, 41, 260–267

Palmer’s paper addresses visual interactive ray tracing (VIRT), specifically referring to Whiteley (2004) and Whiteley and Leung (undated). In these papers, field examples of seismic refraction data from Welcome Reef and Mt Bulga were re-interpreted using VIRTandwavepatheikonaltraveltime(WET)Tomography.These different approaches to near surface refraction interpretation assume very different earth models, from the discrete or ‘blocky’ modelsforVIRTtothecontinuousvelocitymodelsforWET.This enhanced flexibility permits more realistic seismic modelling in near-surface materials, spanning soils, weathered rock and fresh rocks. My comments and discussions address many of the technical deficiencies, inconsistencies, unsubstantiated statements and claims in Palmer’s paper. They are directed at improving the rigour with which near-surface refraction interpretations are undertaken and the quality of these interpretations. In the title, Palmer poses an incompletely defined question. It is not clear actually what ‘visual interactive ray trace’ is,

GkDtree: A group-based parallel update kd-tree for interactive ray tracing

This paper proposes a new group-based acceleration data structure called gkDtree for interactive ray tracing of dynamic scenes. The main idea of the gkDtree is to construct the acceleration structure with a multi-level hierarchy, and to integrate a parallelization approach to result in a faster update and a more efficient tree traversal. A gkDtree can be viewed as a set of kd-trees, each of which is a local acceleration structure corresponding to a group. For a gkDtree, a scene is divided into several groups based on a scene graph. The local acceleration structure of each group involving only dynamic primitives is rebuilt. To achieve higher parallelization, dependencies among groups in different levels are removed before rebuilding occurs in parallel. To enhance the scalability of parallelization, a simple and fast load-balancing scheme is introduced. Furthermore, we apply a variety of accurate SAH (surface area heuristic) algorithms into tree generation for both static and dynamic groups. The experimental results show that a gkDtree has a real-time update performance. It has an update performance that is up to 166 times faster than a kd-tree for our test scenes in a six-core hardware system environment. Furthermore, the results also show that tree traversal performance of a gkDtree is competitive with that of a kd-tree.

Adaptive Interleaved Sampling for Interactive High‐Fidelity Rendering

Abstract Recent advances have made interactive ray tracing (IRT) possible on consumer desktop machines. These advances have brought about the potential for interactive global illumination (IGI) with enhanced realism through physically based lighting. IGI, unlike IRT, has a much higher computational complexity. Furthermore, since non‐primary rays constitute the majority of the computation, the rays are predominantly incoherent, making impractical many of the methods that have made IRT possible. Two methods that have already shown promise in decreasing the computational time of the GI solution are interleaved sampling and adaptive rendering. Interleaved sampling is a generalized sampling scheme that smoothly blends between regular and irregular sampling while maintaining coherence. Adaptive rendering algorithms adjust rendering quality, non‐uniformally, using a guidance scheme. While adaptive rendering has shown to provide speed‐up when used for off‐line rendering it has not been utilized in IRT due to its naturally incoherent nature. In this paper, we combine adaptive rendering and interleaved sampling within a component‐based solution into a new approach we term adaptive interleaved sampling. This allows us to tailor new adaptive heuristics for interleaved sampling of the individual components of the GI solution significantly improving overall performance. We present a novel component‐based IGI framework for which we achieve interactive frame rates for a range of effects such as indirect diffuse lighting, soft shadows and single scatter homogeneous participating media.

Instant Caching for Interactive Global Illumination

Abstract The ability to interactively render dynamic scenes with global illumination is one of the main challenges in computer graphics. The improvement in performance of interactive ray tracing brought about by significant advances in hardware and careful exploitation of coherence has rendered the potential of interactive global illumination a reality. However, the simulation of complex light transport phenomena, such as diffuse interreflections, is still quite costly to compute in real time. In this paper we present a caching scheme, termed Instant Caching, based on a combination of irradiance caching and instant radiosity. By reutilising calculations from neighbouring computations this results in a speedup over previous instant radiosity‐based approaches. Additionally, temporal coherence is exploited by identifying which computations have been invalidated due to geometric transformations and updating only those paths. The exploitation of spatial and temporal coherence allows us to achieve superior frame rates for interactive global illumination within dynamic scenes, without any precomputation or quality loss when compared to previous methods; handling of lighting and material changes are also demonstrated.

The Use of Precomputed Triangle Clusters for Accelerated Ray Tracing in Dynamic Scenes

AbstractIn this paper we present a hybrid algorithm for building the bounding volume hierarchy (BVH) that is used in accelerating ray tracing of animated models. This algorithm precomputes densely packed clusters of triangles on surfaces. Folowing that, a set of clusters is used to rebuild the BVH in every frame. Our approach utilizes the assumption that groups of connected triangles remain connected throughout the course of the animation. We introduce a novel heuristic to create triangle clusters that are designed for high performance ray tracing. This heuristic combines the density of connectivity, geometric size and the shape of the cluster.Our approach accelerates the BVH builder by an order of magnitude rebuilding only the set of clusters that is much smaller than the original set of triangles. The speed‐up is achieved against a ‘brute‐force’ BVH builder that repartitions all triangles in every frame of animation without using any pre‐clustering. The rendering performance is not affected when a cluster contains a few dozen triangles. We demonstrate the real‐time/interactive ray tracing performance for highly‐dynamic complex models.

Compact, Fast and Robust Grids for Ray Tracing

AbstractThe focus of research in acceleration structures for ray tracing recently shifted from render time to time to image, the sum of build time and render time, and also the memory footprint of acceleration structures now receives more attention. In this paper we revisit the grid acceleration structure in this setting. We present two efficient methods for representing and building a grid. The compact grid method consists of a static data structure for representing a grid with minimal memory requirements, more specifically exactly one index per grid cell and exactly one index per object reference, and an algorithm for building that data structure in linear time. The hashed grid method reduces memory requirements even further, by using perfect hashing based on row displacement compression. We show that these methods are more efficient in both time and space than traditional methods based on linked lists and dynamic arrays. We also present a more robust grid traversal algorithm. We show that, for applications where time to image or memory usage is important, such as interactive ray tracing and rendering large models, the grid acceleration structure is an attractive alternative.

Fast, parallel, and asynchronous construction of BVHs for ray tracing animated scenes

Recent developments have produced several techniques for interactive ray tracing of dynamic scenes. In particular, bounding volume hierarchies (BVHs) are efficient acceleration structures that handle complex triangle distributions and can accommodate deformable scenes by updating (refitting) the bounding primitive without restructuring the entire tree. Unfortunately, updating only the bounding primitive can result in a degradation of the quality of the BVH, and in some scenes will result in a dramatic deterioration of rendering performance. In this paper, we present three different orthogonal techniques to avoid that deterioration: (a) quickly rebuilding the BVH using a fast, binning-based approach; (b) a parallel variant of that build to better exploit the multi-core architecture of modern CPUs; (c) asynchronously rebuilding the BVH concurrently with rendering and animation, allowing it to scale to even larger models by stretching the (parallel) BVH build over one or more frames. Our approach is particularly targeted toward future many-core architectures, and allows for flexibly allocating how many cores are used for rebuilding vs. how many are used for rendering.

Seismic refraction characteristics of the Elura ore body and regolith

Major exploration difficulties occur when the distinctive characteristics of ore targets are obscured or modified by physical property variations within the regolith. Improved exploration success in the highly variable Australian regolith requires greater understanding of this medium which can only be achieved with new or improved exploration technologies.The Cobar District of New South Wales is one of the world’s most active mineral exploration regions with a variable regolith. This region has yielded substantial mineral wealth and the Elura ore body is one of the largest massive sulphide deposits to have entered the Cobar regolith. Previous pre-mining, shallow seismic refraction data over this ore body have been re-interpreted using visual interactive ray tracing and wavepath eikonal tomography. This improved interpretation approach has been integrated with the most recent geological knowledge, weathering history and the seismic properties of the shallow ore and host rocks to refine the seismic characteristics of the Elura ore body and regolith. The interpretations have confirmed the earlier qualitative interpretation that the Elura gossan and the altered ore zone form a local, low-velocity plug extending to a depth of ~100 m within the shallower, higher velocity weathered and fresh siltstone host rocks. The margins of this plug are well defined in the refraction interpretation as they form strong seismic wave diffraction sites at the base of the surrounding regolith. The base of this plug, representing the altered massive sulphide ore, also tends to have a lower seismic velocity than the fresh host rocks. Velocity information on the deeper gossan, supergene zone could not be obtained directly from the first-arrival seismic data as this region is laterally hidden. It is clear from this interpretation that the base of the regolith over the Elura ore body and margins are highly irregular and not well represented as a single continuous refractor as required by less sophisticated refraction interpretation approaches.This case study shows that detailed seismic refraction, supported by improved interpretation techniques and petrophysical testing, provide detailed regolith information and have increased exploration potential for massive sulphide targets that enter or are close to the regolith.

Interactive sound rendering in complex and dynamic scenes using frustum tracing

We present a new approach for simulating real-time sound propagation in complex, virtual scenes with dynamic sources and objects. Our approach combines the efficiency of interactive ray tracing with the accuracy of tracing a volumetric representation. We use a four-sided convex frustum and perform clipping and intersection tests using ray packet tracing. A simple and efficient formulation is used to compute secondary frusta and perform hierarchical traversal. We demonstrate the performance of our algorithm in an interactive system for complex environments and architectural models with tens or hundreds of thousands of triangles. Our algorithm can perform real-time simulation and rendering on a high-end PC.

Highly Parallel Fast KD‐tree Construction for Interactive Ray Tracing of Dynamic Scenes

Abstract We present a highly parallel, linearly scalable technique of kd‐tree construction for ray tracing of dynamic geometry. We use conventional kd‐tree compatible with the high performing algorithms such as MLRTA or frustum tracing. Proposed technique offers exceptional construction speed maintaining reasonable kd‐tree quality for rendering stage. The algorithm builds a kd‐tree from scratch each frame, thus prior knowledge of motion /deformation or motion constraints are not required. We achieve nearly real‐time performance of 7‐12 FPS for models with 200K of dynamic triangles at 1024x1024 resolution with shadows and textures.

A Coherent Grid Traversal Approach to Visualizing Particle-Based Simulation Data

We present an approach to visualizing particle-based simulation data using interactive ray tracing and describe an algorithmic enhancement that exploits the properties of these data sets to provide highly interactive performance and reduced storage requirements. This algorithm for fast packet-based ray tracing of multilevel grids enables the interactive visualization of large time-varying data sets with millions of particles and incorporates advanced features like soft shadows. We compare the performance of our approach with two recent particle visualization systems: one based on an optimized single ray grid traversal algorithm and the other on programmable graphics hardware. This comparison demonstrates that the new algorithm offers an attractive alternative for interactive particle visualization.

Comparison of shallow seismic refraction interpretation methods for regolith mapping

A number of shallow refraction interpretation methods are compared in variable regolith conditions using synthetic and published field data. The synthetic model contained a low velocity zone in a depression at the base of the regolith. Independent interpretation with the Reciprocal Method was in reasonable with this model. The Generalised Reciprocal Method performed poorly on this model, both smoothing and considerably underestimating the depth to the simulated regolith base and greatly narrowing the low velocity zone. However, neither the Reciprocal nor Generalised Reciprocal Methods produced valid velocity analyses over the low velocity zone, as diffracted and non-critically refracted wave arrivals are used. Wavefront Eikonal Traveltime Tomography identified the rapid thickening of the regolith over the depression, but introduced an artefact near the low velocity zone, and the regolith base was not easily located. Low wave path densities over the depression identified by this method also indicated that the interpretation should be treated with caution.The field example was over a variable regolith with a faulted contact between rocks of differing weathering characteristics. Visual Interactive Ray Tracing and Wavefront Eikonal Traveltime Tomographic interpretations were in good general agreement for this example. These interpretations differed considerably from the original Generalised Reciprocal Method interpretation that contained a wide low velocity zone at the contact. This is likely to be an artefact of the Generalised Reciprocal Method interpretation process.While our comparisons are not definitive and all the interpretation methods that were compared have deficiencies and limitations they do offer some guidance to improving shallow refraction interpretation for regolith mapping. This is achieved by combining some of the methods and involves the Reciprocal Method, Wavepath Eikonal Traveltime Tomography, and Visual Interactive Ray Tracing. Interesting subsurface features and limitations are highlighted by joint use of ray path displays and wave path density diagrams together with various statistical goodness-of-fit measures to the field data. While this interpretation approach should be more robust, it does not eliminate personal bias nor overcome inherent limitations in the shallow seismic refraction method for regolith mapping, such as the delineation of laterally hidden low velocity zones.

Interactive ray tracing of skinned animations

Recent high-performance ray tracing implementations have already achieved interactive performance on a single PC even for highly complex scenes. However, so far these approaches have been limited to mostly static scenes due to the high cost of updating the necessary spatial index structures after modifying scene geometry. In this paper, we present an approach that avoids these updates almost completely for the case of skinned models as typically used in computer games. We assume that the characters are built from meshes with an underlying skeleton structure, where the set of joint angles defines the character’s pose and determines the skinning parameters. Based on a sampling of the possible pose space we build a static fuzzy kd-tree for each skeleton segment in a fast preprocessing step. This fuzzy kd-tree is then organized into a top-level kd-tree. Together with the skeleton’s affine transformations this multi-level kd-tree allows fast and efficient scene traversal at runtime, while arbitrary combinations of animation sequences can be applied interactively to the joint angles. We achieve a real-time ray tracing performance of up to 15 frames per second at 1024×1024 resolution even on a single processor core.