Accurate and efficient GPU ray‐casting algorithm for volume rendering of unstructured grid data

We present a novel GPU‐based ray‐casting algorithm for volume rendering of unstructured grid data. Our volume rendering system uses a ray‐casting method that guarantees accurate rendering results. We also employ the per‐pixel intersection list concept in the Bunyk algorithm to guarantee an accurate result for non‐convex meshes. For efficient memory access for the lists on the GPU, we represent the intersection lists for all faces as an array with our novel construction algorithm. With the intersection lists, we perform ray‐casting on a GPU, and a GPU thread handles each ray. To increase ray‐coherency in a thread block and improve memory access efficiency, we extend a prior image‐tile‐based work distribution method to fit modern GPU architectures. We also show that a prior approach using a per‐thread local buffer to reduce redundant computation is not appropriate for modern GPU architectures. Instead, we take an on‐demand calculation strategy that achieves better performance even though it allows duplicate computations. We applied our method to three unstructured grid datasets with different characteristics. With a GPU, our method achieved up to 36.5 times higher performance for the ray‐casting process and 19.7 times higher performance for the whole volume rendering process compared with the Bunyk algorithm using a CPU core. Also, our approach showed up to 8.2 times higher performance than a GPU‐based cell projection method while generating more accurate rendering results. These results demonstrate the efficiency and accuracy of our method.     

Fast Hardware-Accelerated Volume Rendering of CT Scans

As CT scanning is a very common medical imaging method, we propose new hardware-based algorithms using GPU (Graphical Processor Unit) programming for rapid visualization. Firstly, 3D volumes are constructed from CT scans. Then volume rendering is used to display anatomical structures via algorithms founded on improved ray casting and 2D textures. Our methods achieve interactive rendering rates and require an ordinary PC with an off-the-shelf graphics card. We expect our approach to be useful to medical practitioners for handling modern, large-scale medical datasets.      

An efficient parallel architecture for ray-tracing

Real time rendering of three-dimensional scenes in high photorealistic details is a hard task, such as in the ray tracing rendering algorithm. In general, the performance achieved by a sequential software-based implementation of ray tracing is far from satisfactory. However, parallel implementations of ray tracing have been enabling reasonable real time performance, as the algorithm is embarrassingly parallel. Thus, a custom parallel design in hardware is likely to achieve an even higher performance. In this paper, we propose a hardware parallel architecture capable of dealing with the main desirable features of ray tracing, such as shadows and reflection effects, imposing low area cost and a promising rendering performance. Such architecture, called GridRT, is based on the Uniform Grid acceleration structure and is intended to deliver massive parallelism through parallel ray-triangle intersection tests as well as parallel processing of many rays. A hardware implementation of the proposed architecture is presented, together with some performance results and resources requirements. The rendering is reduced by 80% using a grid configuration of eight processing elements.     

基于GPU的虚拟内窥镜场景实时绘制算法

为满足影像引导手术(IGS)中高分辨率、海量数据的实时渲染,提出一种基于GPU的虚拟内窥镜场景实时绘制算法。该算法针对虚拟内窥镜渲染数据的特点(管腔数据占总数据比例小,5%左右),首先对图像进行自动分割,得到管腔组织的分割数据;仅将分割后的数据一次载入图像显存,利用光线投射算法进行渲染,并在多GPU负载方面做了优化。充分利用GPU渲染和并行计算的能力,实现了海量数据(1 024×1 024×1 024)的实时渲染。     

基于改进光线投射算法的室内烟雾可视化研究

针对传统光线投射算法在三维场景中绘制大量烟雾数据时存在计算资源消耗大、绘制速度缓慢等一系列问题,提出一种基于改进光线投射算法的室内烟雾可视化方法.将三维数据场按照统一大小划分成均匀的数据块,求出光线穿越数据块时入射点和出射点的中点位置,利用视点和中点之间的距离比例来调整采样频率,从而获得重采样点的位置.再通过对光线上的...     

Computation of Troposphere Slant Delays on a GPU

The computation of ray-traced troposphere delays which can be utilized for space geodetic applications is a time-consuming effort when a large number of rays has to be calculated. On the other hand, computation time can be tremendously reduced when algorithms are capable of supporting parallel processing architectures. Thus, by the use of an off-the-shelf graphics processing unit (GPU), it is demonstrated that troposphere slant delays can be computed very efficiently, without loss of accuracy. An adopted ray-tracing algorithm is presented, and results from GPU computations are compared with those obtained from calculations on a standard personal computer's CPU.     

On-Site Volume Rendering with GPU-Enabled Devices

Now that high-performance computing systems can rely more on a cloud based infrastructure, it becomes much more important to have ubiquitous data processing and visualization capability. This will allow data sharing among numerous clients using shared data repositories through a secure web server. Thanks to the wide availability of GPU support in today’s mobile devices such as smart phones and tablets, as well as the recently published WebGL standard, pervasive computing for high-quality and real-time volume rendering may be realized on such high-performance platforms. We have invented two high-performance volume renderers, namely, single-pass GPU ray caster and fast 3D texture slicer, for both mobile and desktop platforms. Rigorous experiments and performance assessments reveal that the proposed mobile 3D image rendering system outperforms the existing approaches in the literature.     

Precision isosurface rendering of 3D image data

We address the task of rendering by ray tracing the isosurface of a high-quality continuous model of volumetric discrete and regular data. Based on first principles, we identify the quadratic B-spline as the best model for our purpose. The nonnegativity of this basis function allows us to confine the potential location of the isosurface within a binary shell. We then show how to use the space-embedding property of splines to further shrink this shell to essentially a single voxel width. Not all rays traced through a given shell voxel intersect the isosurface; many may only graze it, especially when the ray-tracing vantage point is close to or within the volume to be rendered. We propose an efficient heuristic to detect those cases. We present experiments to support our claims.     

基于二维最大熵阈值分割的体绘制技术研究

针对光线投射体绘制算法存在的运算量大,绘制速度慢的问题,提出了光线投射体绘制过程中对工业CT断层图像原始数据场进行二维最大熵阈值分割预处理的改进,利用二维直方图熵最大化确定阈值的范围,寻找参数的最优组合,结合阈值面积消除法滤除一些噪声将图像二值化,减少重建体数据量,加速光线投射的效率.取得了较好的显示效果.     

基于GPU的工业CT数据场三维纹理映射体绘制算法

本文提出的基于GPU的三维纹理映射算法通过编写顶点程序和片段程序,将传统的基于纹理面片的体绘制算法在GPU中实现.首先将体数据映射为三维纹理并将其载入到显存,接着通过对顶点着色程序和像素着色程序的编写将光线进入点、离开点的计算以及图像的合成运算移入GPU中,最后根据不同的采样点颜色混合公式实现不同的绘制效果.与传统的三...     

基于并行双尺度射线追踪的海面电磁散射计算

利用一种基于双尺度模型(Two Scale Model, TSM)的射线追踪(Ray Tracing, RT)算法(TSM-RT)快速计算电大尺寸海面电磁散射, 与传统的射线追踪算法相比, 该算法能够有效减少射线与面元的求交次数, 提高了计算效率.同时, 为了进一步减少计算时间, 利用图形处理单元(Graphics Processing Unit, GPU)强大的并行处理能力对TSM-RT算法进行加速.计算结果表明:基于GPU的并行TSM-RT算法与基于CPU的串行TSM-RT算法相比计算时间有了很大程度的减少, 获得了很好的加速效果.     

采用GPU加速的三维实体模型绘制

 利用GPU的强大浮点数计算能力和并行处理能力,提出一种完全基于GPU的具有真实感三维实体模型快速绘制方法.本文利用现代图形加速卡中GPU的可编程管线,实现了快速的网格生成及简化.在保证不改变网格的拓扑结构的前提下,调整网格,使能量方程的数值尽量降低,从而大大降低线性曲面中三角形的数量.实验结果表明,该方法能够实现实时的三维实体模型快速绘制,具有重要的应用价值.     

基于GPU加速的深度图像绘制

基于深度图像的绘制(DIBR)广泛应用于虚拟视点的合成,但是目前实现DIBR的算法复杂度都比较高,很难较实时地应用到3DTV系统中。采用单路纹理图像和其对应的深度图像进行虚拟视点的合成,在图形处理单元(GPU)上应用CUDA(Compute Unified Device Architecture)技术实现了基于深度图像的绘制。通过在NVIDIA Telsa C2050图形卡上运行,绘制分辨力1 024×768和640×480的图像速率分别达到了15 f/s(帧/秒)和24 f/s,分别能够准实时或实时地应用到3DTV系统中;同时本文的绘制方法有效地节约了传输带宽,绘制图像的主观质量良好。     

Simulating 3-D lung dynamics using a programmable graphics processing unit.

Medical simulations of lung dynamics promise to be effective tools for teaching and training clinical and surgical procedures related to lungs. Their effectiveness may be greatly enhanced when visualized in an augmented reality (AR) environment. However, the computational requirements of AR environments limit the availability of the central processing unit (CPU) for the lung dynamics simulation for different breathing conditions. In this paper, we present a method for computing lung deformations in real time by taking advantage of the programmable graphics processing unit (GPU). This will save the CPU time for other AR-associated tasks such as tracking, communication, and interaction management. An approach for the simulations of the three-dimensional (3-D) lung dynamics using Green's formulation in the case of upright position is taken into consideration. We extend this approach to other orientations as well as the subsequent changes in breathing. Specifically, the proposed extension presents a computational optimization and its implementation in a GPU. Results show that the computational requirements for simulating the deformation of a 3-D lung model are significantly reduced for point-based rendering.     

复杂轨迹合成孔径雷达后向投影算法图像流GPU成像

相对于基于傅里叶变换的频域成像算法,后向投影( BP)算法因采用时域逐点相干积累,更适合于复杂轨迹合成孔径雷达( SAR)高精度成像。但BP算法计算量巨大,限制了其应用于SAR大场景大数据量快速成像。图形处理器( GPU)具有强大浮点运算和并行处理能力,为大场景BP算法快速成像实现提供了途径。结合GPU并行处理,提出了一种基于图像流的复杂运动SAR大场景BP快速成像处理方法。该方法借助BP算法中图像像素点相互独立处理的特性,采用图像像素点并行及图像流程处理,设计了孔径与图像缓存调度方案,提高SAR大场景大数据BP算法成像效率。仿真和机载实测数据结果验证了方法的有效性,在有限GPU显存条件下实现了8192×8192大场景快速成像,并且成像加速比相对于传统CPU单线程处理可达300倍以上。     

Volumetric attribute filtering and interactive visualization using the Max-Tree representation.

The Max-Tree designed for morphological attribute filtering in image processing, is a data structure in which the nodes represent connected components for all threshold levels in a data set. Attribute filters compute some attribute describing the shape or size of each connected component and then decide which components to keep or to discard. In this paper, we augment the basic Max-Tree data structure such that interactive volumetric filtering and visualization becomes possible. We introduce extensions that allow (1) direct, splatting-based, volume rendering; (2) representation of the Max-Tree on graphics hardware; and (3) fast active cell selection for isosurface generation. In all three cases, we can use the Max-Tree representation for visualization directly, without needing to reconstruct the volumetric data explicitly. We show that both filtering and visualization can be performed at interactive frame rates, ranging between 2.4 and 32 frames per seconds. In contrast, a standard texture-based volume visualization method manages only between 0.5 and 1.8 frames per second. For isovalue browsing, the experimental results show that the performance is comparable to the performance of an interval tree, where our method has the advantage that both filter threshold browsing and isolevel browsing are fast. It is shown that the methods using graphics hardware can be extended to other connected filters.     

视点相关光线投射算法在三维云可视化方面的应用

针对绘制海量云数据时传统光线投射算法计算量大、绘制缓慢等问题,提出了一种基于视点相关光线投射算法的三维云可视化方法。该方法首先采用基于多分辨率方法的数据预处理策略,然后采用基于视点相关系数的自适应采样频率计算方法确定重采样点的位置,并利用三阶段插值算法计算重采样点的值,最后采用基于块重要性加权香农熵的二维传输函数完成颜色值和不透明度的映射关系,从而实现图像的合成。实验结果表明,该方法计算复杂度低、执行效率高,与现有的光线投射算法相比,不仅图像的重构质量得到了提高,绘制时间也减少了约30%。     

Ray tracing with PO/PTD for RCS modeling of large complex objects

The present paper deals with a new efficient approach in order to assess the simulation of scattered fields from arbitrary metallic objects. The basic idea is to combine a ray tracing algorithm with the principles of physical optics (PO) and the physical theory of diffraction (PTD). The ray tracing algorithm stochastically launches discrete rays and uses a ray density normalization. In order to perform simulations at finite objects the PO/PTD formulation is required. Thus, fast intersection routines can be implemented, while the ray density formulation reduces the PO and PTD integrals to a pure sum of ray contributions. Simulation results obtained with this model are verified by comparison with both exact simulations using a method of moments (MoM) code and measurement results, proving an excellent accuracy and fast computation even at complex objects. With this asymptotic approach, scattering properties of large objects that are too complex for exact methods can be analyzed with rather moderate computation efforts. Typical applications include the simulation of low observability (LO) designs as well as the generation of databases for identifying unknown aircraft by their radar signature.     

Real-time video-based rendering from uncalibrated cameras using plane-sweep algorithm

In this paper, we present a new online video-based rendering (VBR) method that creates new views of a scene from uncalibrated cameras. Our method does not require information about the cameras intrinsic parameters. For obtaining a geometrical relation among the cameras, we use projective grid space (PGS) which is 3D space defined by epipolar geometry between two basis cameras. The other cameras are registered to the same 3D space by trifocal tensors between these basis cameras. We simultaneously reconstruct and render novel view using our proposed plane-sweep algorithm in PGS. To achieve real-time performance, we implemented the proposed algorithm in graphics processing unit (GPU). We succeed to create novel view images in real-time from uncalibrated cameras and the results show the efficiency of our proposed method.     

一种基于射线追踪的时变效应模拟方法

本文探讨了自然界广泛存在的时变效应的模拟问题,实现了一种基于射线追踪方法的时变效应渲染方法.该方法使用Surfels技术对模型表面进行重构和设置属性值,从射线源发射出相应属性值的射线,当射线碰撞到模型表面时将射线属性和模型表面元素属性交换.根据模型表面元素值,选取适当的纹理通过相应的纹理技术进行纹理映射,实现模型表面再次渲染,使模型实现时变效应.针对建筑物场景的实验结果验证了该方法的正确性.