Ray Casting Research Articles

Hierarchical Visibility for Virtual Reality

We introduce a novel primary visibility algorithm based on ray casting that provides real time performance and a feature set well suited for rendering virtual reality. The flexibility provided by our approach allows for a variety of features such as lens distortion, sub-pixel rendering, very wide field of view, foveation and stochastic depth of field blur to be implemented and composed naturally while maintaining real time performance. In contrast, the current rasterization pipelines implemented in hardware require multiple passes and/or post processing to approximate these features and current highly optimized ray tracers, which primarily focus on Monte Carlo path tracing, do not achieve real time performance on current VR displays (1080x1200x2@90hz). Our approach uses a bounding volume hierarchy acceleration and a two level frustum culling/entry point search algorithm to optimize the traversal of coherent primary visibility rays. We introduce an adaptation of MSAA for raycasting that significantly lowers memory bandwidth, we leverage an AVX optimized CPU traversal to perform the majority of culling and an optimized CUDA GPU implementation for triangle intersection, multi-sample antialiasing, and shading. The implementation provides support for animation and physically-based shading and lighting. We believe this approach presents a concrete, viable alternative to rasterization that is significantly better suited to rendering for virtual and augmented reality. In order to engage the community, we have released our implementation under an open-source license.

OSG Based Real-time Volume Rendering Algorithm for Electromagnetic Environment

The electromagnetic environment is widespread and very complex. Due to the invisibility of the electromagnetic environment, the direct volume rendering technique can be used to show the complex electromagnetic environment. In this paper, the Irregular Terrain Model (ITM) electromagnetic wave propagation model and the coordinate transformation are used to simulate the electromagnetic environment. In the three-dimensional digital GlobelGIS platform, the improved ray casting algorithm is applied to render the electromagnetic field and design the transfer function which is used to express different electromagnetic power intensity with different colors and opacities. Considering the problem that the traditional ray casting algorithm, which uses the OpenGL graphical interface, cannot be integrated into the GlobelGIS platform directly, so the ray casting algorithm that based on OSG and the GLSL shading language for hardwareacceleration are proposed. The simulation results show that this method can render multi-source electromagnetic environment on the GlobelGIS platform in real-time and interactively. The volume rendering algorithm is not only suitable for the rendering of electromagnetic, but also for the visualization of volume data in other applications.

GPU-accelerated generation and rendering of multi-level voxel representations of solid models

Solid models traditionally use boundary-representation (B-rep) to define and model their geometry. However, performing modeling operations such as Boolean operations or computing point membership classification with B-rep is computationally intensive, since B-reps do not have volumetric information. Voxelized representations, on the other hand, can be extended to include volumetric information of solid models. However, in order to use voxelized representations for solid modeling, efficient methods for voxelizing a B-rep solid model needs to be developed. In this paper, we present GPU-accelerated methods for creating and rendering a multi-level voxelization of a solid model that can be used for modeling operations. We describe two GPU-accelerated algorithms; one for creating a multi-level voxelization given a B-rep of a solid model and another for ray casting to render the multi-level voxelization of the solid model. We describe compact and flat data structures that can be used to store the multi-level voxelization data and can be efficiently retrieved in parallel by GPU-algorithms for rendering and modeling operations. The GPU-accelerated multi-level voxelization method can generate models with an effective voxel count of up to 8 billion voxels. In addition, the GPU voxelization algorithm is more than 40x faster than the CPU implementation in generating the voxelization. Finally, we outline a few applications for the voxel representation, which include fast point-membership classification, volume computation, and collision detection.

Travel time computations using a compact eikonal equation for vertical transverse isotropic media

ABSTRACTEikonal solvers often have stability problems if the velocity model is mildly heterogeneous. We derive a stable and compact form of the eikonal equation for P‐wave propagation in vertical transverse isotropic media. The obtained formulation is more compact than other formulations and therefore computationally attractive. We implemented ray shooting for this new equation through a Hamiltonian formalism. Ray tracing based on this new equation is tested on both simple as well as more realistic mildly heterogeneous velocity models. We show through examples that the new equation gives travel times that coincide with the travel time picks from wave equation modelling for anisotropic wave propagation.

Interactive CNC simulation using distance fields

ABSTRACTReal-time simulation of numerical control machining is important to the virtual manufacturing process. It is used to optimise the product design and production plan on a virtual environment, thus saving on the overall manufacturing cost and time. A real-time geometric simulation is desirable because the faster is the simulation, the greater is its capabilities to detect errors. Real-time interactive simulation allows faster iterations in the design phase. However, a precise and real-time interactive simulation is a difficult problem because it requires an efficient representation for complex dynamic volumes while offering interactive real-time rendering of the scene. This research proposes a novel solution for precise and real-time interactive CNC (Computer Numerical Control) simulation using signed distance fields (SDFs) with a data structure for dynamic narrow-band level sets called VDB. The real-time interactive rendering is then solved with a ray-casting algorithm. Tests were performed and SDF was concluded to provide efficient Boolean operations and memory usage, and real-time interactive rendering of its models was possible using ray casting.

Characteristic visualization of the micro/mesoscale liquid ethanol diffusion flame by using deflection tomography

The micro/mesoscale combustion system of liquid ethanol and the visualization measurement system of flame were designed and constructed on the basis of the microscale combustion theory of liquid fuels. The characteristics of the micro/mesoscale liquid ethanol diffusion flame were investigated experimentally. The flow fields of flame were visualized and measured using deflection tomography. An image sampling system was proposed for deflection tomography to obtain deflectograms and flame images in one shot. The deflection angles of rays were extracted by the wave-front retrieval of deflectograms, which was suitable for micro/mesoscale combustion. The two-dimensional temperature distributions were reconstructed using the deflection angle revision reconstruction algorithm. The three-dimensional distribution of temperature and structure of flame were obtained using a visualization toolkit equipped with the marching cube and ray casting algorithms. At the same diameter of burner, the height, width and peak temperature of flame did not change significantly as the flow rate of fuel increased in the stable combustion stage. In the oscillation combustion stage, the height and width of flame gradually increased, the peak temperature increased firstly and then decreased, and the oscillation cycle of the flame decreased with the increase in the flow rate of fuel. Under equal flow rate of fuel, the height and width of flame were independent of the diameter of burner in the oscillation combustion stage. At the same time, the distribution of temperature and the oscillation period of flame were closely related to the diameter of burner. The pulsating instability of oscillating flame interacted highly with the heat exchange effect between the flame and the liquid fuel.

Real-time visualization and interaction with static and live optical coherence tomography volumes in immersive virtual reality.

Virtual reality (VR) head-mounted displays are an attractive technology for viewing intrasurgical optical coherence tomography (OCT) volumes because they liberate surgeons from microscope oculars. We demonstrate real-time, interactive viewing of OCT volumes in a commercial HTC Vive immersive VR system using previously reported ray casting techniques. Furthermore, we show interactive manipulation and sectioning of volumes using handheld controllers and guidance of mock surgical procedures in porcine eyes exclusively within VR. To the best of our knowledge, we report the first immersive VR-OCT viewer with stereo ray casting volumetric renders, arbitrary sectioning planes, and live acquisition support. We believe VR-OCT volume displays will advance ophthalmic surgery towards VR-integrated surgery.

Automated brain extraction and immersive exploration of its layers in virtual reality for the rhesus macaque MRI data sets

AbstractAs we know, the rhesus macaque as a nonhuman primate is quite similar to a human being in genetics. Moreover, it has become essential in animal model anatomy and physiology in many modern medicine research such as the cardiovascular and cerebrovascular diseases in the recent years. This paper describes a pipeline from the raw rhesus macaque brain magnetic resonance imaging data to intuitive 3D inspection of its layers. Brain extraction is an initial step for subsequent analyses, but most of the existing methods so far are designed for human brain, which does not work well with the rhesus macaque. Firstly, we propose a reliable and efficient method to extract the brain from magnetic resonance imaging data sets based on dividing the brain into blocks. Then, we design a trapezoid opacity transfer function based on Compute Unified Device Architecture (CUDA)‐based real‐time volume ray casting, which is dedicated to volume rendering to make the inspection more intuitive. Besides, for an immersive exploration in virtual reality benefits understanding the volumetric data sets, so we also design a layer filter for the segmented rhesus macaque brain data sets, which facilitates the inspection of the interior in Region of Interest (ROI) by an intuitive bimanual interaction via a Leap Motion sensor. Our experiments prove usability and efficiency.

QUADOR: QUADric-Of-Revolution beams for lattices

Objects with designed internal structure often consist a lattice of beams, in which the surface of each beam smoothly connects two spheres, possibly of different radii. We propose a geometric model for these beams that provides a compromise between shape flexibility and ease of computation: each beam is either a single quadric of revolution (“quador”), or two smoothly connected ones (“biquador”). Quador and biquador beams can be specified using easily adjustable parameters. They simplify and accelerate several common geometric queries, including point classification, ray casting, planar slicing, and boundary evaluation. We compare quadors and biquadors with other possible beam shapes, and show that these alternatives have either reduced flexibility or increased computational cost. We advocate decomposing the lattice into an assembly of hubs, each hub defined as the union of a sphere with the half-beams (stumps) that connect to it. We describe approaches for computing an exact polyhedral Constructive Solid Trimming expression of each face and the exact edges and vertices of the hub.

Compressed Animated Light Fields with Real-Time View-Dependent Reconstruction.

We propose an end-to-end solution for presenting movie quality animated graphics to the user while still allowing the sense of presence afforded by free viewpoint head motion. By transforming offline rendered movie content into a novel immersive representation, we display the content in real-time according to the tracked head pose. For each frame, we generate a set of cubemap images per frame (colors and depths) using a sparse set of of cameras placed in the vicinity of the potential viewer locations. The cameras are placed with an optimization process so that the rendered data maximise coverage with minimum redundancy, depending on the lighting environment complexity. We compress the colors and depths separately, introducing an integrated spatial and temporal scheme tailored to high performance on GPUs for Virtual Reality applications. A view-dependent decompression algorithm decodes only the parts of the compressed video streams that are visible to users. We detail a real-time rendering algorithm using multi-view ray casting, with a variant that can handle strong view dependent effects such as mirror surfaces and glass. Compression rates of 150:1 and greater are demonstrated with quantitative analysis of image reconstruction quality and performance.

Visualising volumetric fractals

Fractal images have for many years been a rich source of exploration by those in computer science who also have an interest in graphics. They often served as a way of testing the performance of new computing hardware and to explore the capabilities of emerging display technologies. While there have been forays by some into 3D geometric fractals, the 3D equivalents of the Mandelbrot set have been largely ignored. This is largely due to the lack of suitable tools for rendering these sets except perhaps as isosurfaces, a rather unsatisfactory and limited representation. The following will illustrate the application of GPU based raycasting, a now relatively standard approach to volume rendering, to the representation of volumetric fractals. Leveraging existing software that has been designed for general volume visualisation allows the interested 3D fractal explorer to focus on the mathematical generation of the volume data rather than reinventing the entire volume rendering pipeline.

A Generative Model for Volume Rendering.

We present a technique to synthesize and analyze volume-rendered images using generative models. We use the Generative Adversarial Network (GAN) framework to compute a model from a large collection of volume renderings, conditioned on (1) viewpoint and (2) transfer functions for opacity and color. Our approach facilitates tasks for volume analysis that are challenging to achieve using existing rendering techniques such as ray casting or texture-based methods. We show how to guide the user in transfer function editing by quantifying expected change in the output image. Additionally, the generative model transforms transfer functions into a view-invariant latent space specifically designed to synthesize volume-rendered images. We use this space directly for rendering, enabling the user to explore the space of volume-rendered images. As our model is independent of the choice of volume rendering process, we show how to analyze volume-rendered images produced by direct and global illumination lighting, for a variety of volume datasets.

Progressive ray casting for volumetric models on mobile devices

Mobile devices have experienced an incredible market penetration in the last decade. Currently, medium to premium smartphones are relatively affordable devices. With the increase in screen size and resolution, together with the improvements in performance of mobile CPUs and GPUs, more tasks have become possible. In this paper we explore the rendering of medium to large volumetric models on mobile and low performance devices in general. To do so, we present a progressive ray casting method that is able to obtain interactive frame rates and high quality results for models that not long ago were only supported by desktop computers.

GPU ray casting method for visualizing 3D pipelines in a virtual globe

ABSTRACTPipelines are an important part of urban infrastructure development. As part of a virtual globe (VG), the high-efficiency and high-quality visualization of 3D large-scale and high-density urban pipelines is of great importance. This paper proposes a GPU-based pipeline ray casting method for the visualization of urban-scale pipelines in the framework of a VG. The method involves the initial partitioning of the pipeline data into tiles, based on the relationship between the pipeline layer scale and the discrete global grid system (DGGSs). The pipeline centerline in each tile is then segmented and encoded, and a coarser pipeline bounding volume is subsequently constructed using a geometry shader. Finally, the fine 3D pipeline is rendered using a pixel shader. The results of the experimental implementation of the proposed method show that it satisfies the requirements for the multiscale visualization of pipelines in a VG. Moreover, compared with the traditional polygon-based method, the method facilitates a 20% increase in rendering frame rate for the same pixel level accuracy display effect. It also enables the visualization of the thickness of the 3D pipeline without any obvious effect on the rendering efficiency.

GPU-based focus-driven multi-coordinates viewing system for large volume data visualisation

In this paper, we are presenting a generalised contactless interactive graphics processing unit (GPU) accelerated compute unified device architecture (CUDA) based focus and context visualisation approach with displaying the inner anatomy of the large scale visible human male dataset in multi-coordinate viewing system (MCVS). The focusing area has been achieved by 3D Cartesian region of interest (ROI). The large dataset has been structured by using Octree method. The volume rendering part has been done by using an improved ray intersection cube method for voxels with the ray casting algorithm. The final results would allow the doctors to diagnose and analyse the atlas of 8-bit CT-scan data visualisation with efficient frame rates of rendering speed. The system is tested on ten multiple sized of 3D medical datasets ranging from 10 MB to 3.15 GB. The scope of this system is to explore of the human body for surgery purpose.

Intersection Warning System for Occlusion Risks Using Relational Local Dynamic Maps

This work addresses the task of risk evaluation in traffic scenarios with limited observability due to restricted sensorial coverage. Here, we concentrate on intersection scenarios that are difficult to access visually. To identify the area of sight, we employ ray casting on a local dynamic map providing geometrical information and road infrastructure. Based on the area with reduced visibility, we first model scene entities that pose a potential risk without being visually perceivable yet. Then, we predict a worst-case trajectory in the survival analysis for collision risk estimation. Resulting risk indicators are utilized to evaluate the driver's current behavior, to warn the driver in critical situations, to give suggestions on how to act safely or to plan safe trajectories. We validate our approach by applying the resulting intersection warning system on real world scenarios. The proposed system's behavior reveals to mimic the general behavior of a correctly acting human driver.

GPU-based focus-driven multi-coordinates viewing system for large volume data visualisation

In this paper, we are presenting a generalised contactless interactive graphics processing unit (GPU) accelerated compute unified device architecture (CUDA) based focus and context visualisation approach with displaying the inner anatomy of the large scale visible human male dataset in multi-coordinate viewing system (MCVS). The focusing area has been achieved by 3D Cartesian region of interest (ROI). The large dataset has been structured by using Octree method. The volume rendering part has been done by using an improved ray intersection cube method for voxels with the ray casting algorithm. The final results would allow the doctors to diagnose and analyse the atlas of 8-bit CT-scan data visualisation with efficient frame rates of rendering speed. The system is tested on ten multiple sized of 3D medical datasets ranging from 10 MB to 3.15 GB. The scope of this system is to explore of the human body for surgery purpose.

Robot-Assisted Decompressive Laminectomy Planning Based on 3D Medical Image

The decompressive laminectomy is a common treatment for lumbar spinal stenosis. Generally, surgeons use grinding tools to remove laminae under the guidance of intraoperative medical images. To improve accuracy and reduce surgeons’ burdens, robot-assisted surgery is gaining acceptance. This paper proposes a method to plan grinding paths and velocities based on 3-D medical images in the context of robot-assisted decompressive laminectomies. As the lesion areas to be grinded are irregular, an interactive method with 3-D reconstruction is designed for surgeons to transfer discrete information about grinding paths and velocities to the robot system. The path generation strategy is based on a ray casting algorithm after space registrations, while the velocity generation strategy is based on the virtual force and mechanical analysis is used to optimize temporal efficiency and stability. A complete system is developed to test and explore the feasibility of this method. Results suggest that robot-assisted decompressive laminectomies can be performed well.

Towards an Optimal Method for Dynamic Planar Point Location

We describe a fully dynamic linear-space data structure for point location in connected planar subdivisions, or more generally vertical ray shooting among nonintersecting line segments, that suppor...

X-ray system simulation software tools for radiology and radiography education

ObjectivesTo develop x-ray simulation software tools to support delivery of radiological science education for a range of learning environments and audiences including individual study, lectures, and tutorials. MethodsTwo software tools were developed; one simulated x-ray production for a simple two dimensional radiographic system geometry comprising an x-ray source, beam filter, test object and detector. The other simulated the acquisition and display of two dimensional radiographic images of complex three dimensional objects using a ray casting algorithm through three dimensional mesh objects. Both tools were intended to be simple to use, produce results accurate enough to be useful for educational purposes, and have an acceptable simulation time on modest computer hardware. The radiographic factors and acquisition geometry could be altered in both tools via their graphical user interfaces. A comparison of radiographic contrast measurements of the simulators to a real system was performed. ResultsThe contrast output of the simulators had excellent agreement with measured results. The software simulators were deployed to 120 computers on campus. ConclusionsThe software tools developed are easy-to-use, clearly demonstrate important x-ray physics and imaging principles, are accessible within a standard University setting and could be used to enhance the teaching of x-ray physics to undergraduate students. Advances in knowledgeCurrent approaches to teaching x-ray physics in radiological science lack immediacy when linking theory with practice. This method of delivery allows students to engage with the subject in an experiential learning environment.