Lattice-Based Volumetric Global Illumination
Feng Qiu, Fang Xu, Zhe Fan, Neophytou Neophytos, Arie Kaufman, and Klaus Mueller
IEEE Transaction on Visualization and Computer Graphics (Special issue IEEE Visualization Conference 2007), 13(6):1576-1583, 2007.

Abstract: We describe a novel volumetric global illumination framework based on the Face-Centered Cubic (FCC) lattice. An FCClattice has important advantages over a Cartesian lattice. It has higher packing density in the frequency domain, which translates tobetter sampling efficiency. Furthermore, it has the maximal possible kissing number (equivalent to the number of nearest neighbors ofeach site), which provides optimal 3D angular discretization among all lattices. We employ a new two-pass (illumination and rendering) global illumination scheme on an FCC lattice. This scheme exploits the angular discretization to greatly simplify the computation inmultiple scattering and to minimize illumination informationstorage. The GPU has been utilized to further accelerate therendering stage. We demonstrate our new framework with participatingmedia and volume rendering with multiple scattering, where both aresignificantly faster than traditional techniques with comparablequality.(Full Paper)

Flow Simulation with Locally-Refined LBM
Ye Zhao, Feng Qiu, Zhe Fan and Arie Kaufman
Proceeding of ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games, pp.181–188, 2007.

Abstract: We simulate 3D fluid flow by a locally-refined lattice Boltzmann method (LBM) on graphics hardware. A low resolution LBM simulation running on a coarse grid models global flow behavior of the entire domain with low consumption of computational resources. For regions of interest where small visual details are desired, LBM simulations are performed on fine grids, which are separate grids superposed on the coarse one. The flow properties on boundaries of the fine grids are determined by the global simulation on the coarse grid. Thus, the locally refined fine-grid simulations follow the global fluid behavior, and model the desired small-scale and turbulent flow motion with their denser numerical discretization. A fine grid can be initiated and terminated at any time while the global simulation is running. It can also move inside the domain with a moving object to capture small-scale vortices caused by the object. Besides the performance improvement due to the adaptive simulation, the locally-refined LBM is suitable for acceleration on contemporary graphics hardware (GPU), since it involves only local and linear computations. Therefore, our approach achieves fast and adaptive 3D flow simulation for computer games and other interactive applications. (Full Paper)

Computer-aided Detection of Colonic Polyps Using Volume Rendering
Wei Hong, Feng Qiu, Joseph Marino, and Arie Kaufman
Proceeding of SPIE Medical Imaging, 2007.

Abstract: This work utilizes a novel pipeline for the computer-aided detection (CAD) of colonic polyps, assisting radiologists in locating polyps when using a virtual colonoscopy system. Our CAD pipeline automatically detects polyps while reducing the number of false positives (FPs). It integrates volume rendering and conformal colon flattening with texture and shape analysis. The colon is first digitally cleansed, segmented, and extracted from the CT dataset of the abdomen. The colon surface is then mapped to a 2D rectangle using conformal mapping. Using this colon flattening method, the CAD problem is converted from 3D into 2D. The flattened image is rendered using a direct volume rendering of the 3D colon dataset with a translucent transfer function. Suspicious polyps are detected by applying a clustering method on the 2D volume rendered image. The FPs are reduced by analyzing shape and texture features of the suspicious areas detected by the clustering step. Compared with shape-based methods, ours is much faster and much more efficient as it avoids computing curvature and other shape parameters for the whole colon wall. We tested our method with 178 datasets and found it to be 100% sensitive to adenomatous polyps with a low rate of FPs. The CAD results are seamlessly integrated into a virtual colonoscopy system, providing the radiologists with visual cues and likelihood indicators of areas likely to contain polyps, and allowing them to quickly inspect the suspicious areas and further exploit the flattened colon view for easy navigation and bookmark placement.

Colonoscopy Simulation
Wei Hong, Jianning Wang, Feng Qiu, Arie Kaufman and John Anderson
Proceeding of SPIE Medical Imaging, 2007.

Abstract: Effective colonoscopic screening for polyps with optical or virtual means requires adequate visualization of the entire colon surface. The purpose of this study is to investigate by simulation the degree of colon surface coverage during a routine optical colonoscopy (OC). To simulate OC, a generic wide angle and fisheye camera model is used to calibrate the fisheye lens of an Olympus endoscope with a field of view of 140 degrees. Then, the colonoscopy procedure is simulated using volume rendering fly-through along the hugging corner path in the retrograde direction. This shortest path is computed using the segmented and cleansed colon CT datasets. A large number of virtual fisheye cameras are placed along the shortest path to simulate the OC. At each camera position, a discrete volumetric ray-casting method is used to determine which triangles can be seen from the camera. Then, the percentage of the covered colon surface of the OC simulation is computed. Surface coverage at this point may serve as a rough estimate of readily visualized mucosa in a standard OC examination. We also compute the percentage of the covered colon surface for the virtual colonoscopy (VC) by placing virtual pinhole cameras on the central path of the colon and flying in only the antegrade direction as well as flying in both antegrade and retrograde directions. Our simulation study reveals that about 23% of the colon surface is missed in the standard OC examination and about 9% of the colon surface is missed in the VC examination when navigating in both directions.

Visual Simulation of Heat Shimmering and Mirage
Ye Zhao, Yiping Han, Zhe Fan, Feng Qiu, Yu-chuan Kuo, Arie Kaufman and Klaus Mueller
IEEE Transactions on Visualization and Computer Graphics , 13(1):179-189, 2007.

Abstract: We provide a physically-based framework for simulating the natural phenomena related to heat interaction between objects and the surrounding air. We introduce a heat transfer model between the heat source objects and the ambient flow environment, which includes conduction, convection, and radiation. The heat distribution of the objects is represented by a novel temperature texture. We simulate the thermal flow dynamics that models the air flow interacting with the heat by a hybrid thermal lattice Boltzmann model (HTLBM). The computational approach couples a multiple-relaxation-time LBM (MRTLBM) with a finite difference discretization of a standard advection-diffusion equation for temperature. In heat shimmering and mirage, the changes in the index of refraction of the surrounding air are attributed to temperature variation. A nonlinear ray tracing method is used for rendering. Interactive performance is achieved by accelerating the computation of both the MRTLBM and the heat transfer, as well as the rendering on contemporary graphics hardware (GPU). (Full Paper)

Melting and Flowing in Multiphase Environment
Ye Zhao, Lujing Wang, Feng Qiu, Arie Kaufman and Klaus Mueller
Computers & Graphics , 30(4):519-528, 2006.

Abstract: This paper presents a method to simulate the melting and flowing phenomena with different materials in multiple phases. In such a multiphase environment, solid objects are melted because of heating and the melted liquid flows while interacting with the ambient air flow. Our simulation is based on a modified lattice Boltzmann method (LBM), where the fluid dynamics of the air flow and the melted liquid is modeled within a common lattice framework. Therefore, no particular front tracking methods are required for the liquid-air interface. The liquid-solid and air-solid interfaces are implemented as curved boundaries in the LBM, which can accommodate arbitrarily shaped solid objects. Heat transfer is incorporated with a finite difference discretization of a standard diffusion-advection equation simulating the temperature evolution. The temperature and body forces (gravity and surface tension) are easily applied by adopting a new version of the LBM: multiple-relaxation-time LBM (MRTLBM). The melting and flowing behavior is controlled by the heat source, the viscosity and the body forces. All the numerical computations in our method are local and parallelizable, therefore, interactive speed is achieved by hardware acceleration on the contemporary graphics hardware (GPU). (Full Paper)

Conformal Virtual Colon Flattening
Wei Hong, Xianfeng Gu, Feng Qiu, Miao Jin, and Arie Kaufman
Proceeding of ACM Symposium on Solid and Physical Modeling, pp. 85-93, 2006.

Abstract: We present an efficient colon flattening algorithm using conformal structure, which is angle-preserving and minimizes the global distortion. Moreover, our algorithm is general which can handle high genus surfaces. First, the colon wall is segmented and extracted from the CT dataset. The topology noise (i.e., minute handle) is located and removed automatically. The holomorphic 1-form, a pair of orthogonal vector fields, is then computed on the 3D colon surface mesh using the conjugate gradient method. The colon surface is cut along a vertical trajectory traced using the holomorphic 1-form. Consequently, the 3D colon surface is conformal mapped to a 2D rectangle. The flattened 2D mesh is then rendered using a direct volume rendering method accelerated with the GPU. Our algorithm is tested with a number of CT datasets of real pathological cases, and gives consistent results. We demonstrated that the shape of the polyps is well preserved on the flattened colon images, which provides an efficient way to enhance the navigation of a virtual colonoscopy system. (Full Paper)

A Pipeline for Computer Aided Polyp Detection
Wei Hong, Feng Qiu, and Arie Kaufman
IEEE Transactions on Visualizaiton and Computer Graphics, 12(5):861-868, 2006.

Abstract: We present a novel pipeline for computer-aided detection (CAD) of colonic polyps by integrating texture and shape analysis with volume rendering and conformal colon flattening. Using our automatic method, the 3D polyp detection problem is converted into a 2D pattern recognition problem. The colon surface is first segmented and extracted from the CT data set of the patient's abdomen, which is then mapped to a 2D rectangle using conformal mapping. This flattened image is rendered using a direct volume rendering technique with a translucent electronic biopsy transfer function. The polyps are detected by a 2D clustering method on the flattened image. The false positives are further reduced by analyzing the volumetric shape and texture features. Compared with shape based methods, our method is much more efficient without the need of computing curvature and other shape parameters for the whole colon surface. The final detection results are stored in the 2D image, which can be easily incorporated into a virtual colonoscopy (VC) system to highlight the polyp locations. The extracted colon surface mesh can be used to accelerate the volumetric ray casting algorithm used to generate the VC endoscopic view. The proposed automatic CAD pipeline is incorporated into an interactive VC system, with a goal of helping radiologists detect polyps faster and with higher accuracy. (link)

Visual Simulation of Chemical Garden
Xiaoming Wei, Feng Qiu, Wei Li, Suzanne Yoakum-Stover and Arie Kaufman
Proceeding of Computer Graphics International, pp. 74-81, 2005.

Abstract: We present a visualization and modeling system for the creation of chemical gardens. A chemical garden is a collection of plant-like structures formed when placing a soluble metal salt in an aqueous solution of sodium silicate. An accurate simulation of the chemical reaction of the metal salt and the physical behavior of the surrounding sodium silicate solution flow are complicated and time-consuming. Instead, in our system we use and propose a simplified 3D cellular automata (CA) approach to model the growing process of a chemical garden and its interaction with the solution flow. The input of our system is the shape and types of various soluble metal salts. Our program supports the visualization of the growth and formation of the chemical garden. The interactive rendering result on a texture mapping hardware also helps the user in observing and creating a desirable chemical garden. (link)

GPU-based Object-Order Ray-Casting for Large Datasets
Wei Hong, Feng Qiu and Arie Kaufman
Proceeding of International Workshop on Volume Graphics, pp.177-185, 2005.

Abstract: We propose a GPU-based object-order ray-casting algorithm for the rendering of large volumetric datasets, such as the Visible Human CT datasets. A volumetric dataset is decomposed into small sub-volumes, which are then
organized using a min-max octree structure. The small sub-volumes are stored in the leaf nodes of the min-max octree, which are also called cells. The cells are classified using a transfer function, and the visible cells are then loaded into the video memory or the AGP memory. The cells are sorted and projected onto the image plane front to back. The cell projection is implemented using a volumetric ray-casting algorithm on the GPU. In order to make the cell projection more efficient, we devise a propagation method to sort cells into layers. The cells within the same layer are projected at the same time. We demonstrate the efficiency of our algorithm using the Visible Human datasets and a segmented photographic brain dataset on commodity PCs. (link)

GPU Cluster For High Performance Computing
Zhe Fan, Feng Qiu, Arie Kaufman, and Suzanne Yoakum-Stover
Proceeding of the ACM / IEEE SC2004 Conference, Pittsburgh PA

Abstract: Inspired by the attractive Flops/dollar ratio and the incredible growth in the speed of modern graphics processing units (GPUs), we propose to use a cluster of GPUs for high performance scientific computing. As an example application, we have developed a parallel flow simulation using the lattice Boltzmann model (LBM) on a GPU cluster and have simulated the dispersion of airborne contaminants in the Times Square area of New York City. Using 30 GPU nodes, our simulation can compute a 480x400x80 LBM in 0.31second/step, a speed which is 4.6 times faster than that of our CPU cluster implementation. Besides the LBM, we also discuss other potential applications of the GPU cluster, such as cellular automata, PDE solvers, and FEM. (Full paper, 1,915K)

Dispersion Simulation And Visualization For Urban Security
Feng Qiu, Ye Zhao, Zhe Fan, Xiaoming Wei, Haik Lorenz, Jianning Wang, Suzanne Yoakum-Stover, Arie Kaufman, and Klaus Mueller
Proceeding of IEEE Visualization, pp. 553-560, 2004.

Abstract: In this paper, we present a system for simulating and visualizing the propagation of dispersive contaminants with an application to urban security. In particular, we simulate airborne contaminant propagation in open environments characterized by sky-scrapers and deep urban canyons. Our approach is based on the Multiple Relaxation Time Lattice Boltzmann Model (MRTLBM), which can efficiently handle complex boundary conditions such as buildings. In addition, we model thermal effects on the flow field using the hybrid thermal MRTLBM. Our approach can also accommodate readings from various sensors distributed in the environment and adapt the simulation accordingly. We accelerate the computation on the GPU and efficiently render many buildings using small textures. We render the contaminant smoke with self-shadowing composited with the textured buildings. (Full paper, 4,385K)

Fast Hybrid Approach for Texturing Point Models
Haitao Zhang, Feng Qiu , Arie Kaufman
Computer Graphics Forum, 23(4):715-725, 2004.

Abstract: We present three methods for texturing point models from sample textures. The first method, the point parameterization method, uses a fast distortion-bounded parameterization algorithm to flatten the point model’s surface into one or more 2D patches. The sample texture is mapped onto these patches and alpha blending is used to minimize the discontinuity in the gaps between the patches. The second method is based on neighborhood matching where a color is assigned to each point by searching the best match within an irregular neighborhood. The hybrid method combines the former two methods, capitalizing on the advantages of both. The point parameterization method is used first to color most of the points, and the point neighborhood matching method is then applied to the points belonging to the gaps between the parameterized patches to minimize the discontinuity. We opt for fast texture generation, while some discontinuities may appear in the gaps of anisotropic textures. (Full paper, 389K)

Lattice-Based Flow Field Modeling
Xiaoming Wei, Ye Zhao, Zhe Fan, Wei Li, Feng Qiu, Suzanne Yoakum-Stover, and Arie Kaufman
IEEE Transactions on Visualization and Computer Graphics, 10(6):719-729, 2004.

Abstract: We present an approach for simulating the natural dynamics that emerge from the interaction between a flow field and immersed objects. We model the flow field using the Lattice Boltzmann Model (LBM) with boundary conditions appropriate for moving objects, and accelerate the computation on commodity graphics hardware to achieve real-time performance. The boundary conditions mediate the exchange of momentum between the flow field and the moving objects. We demonstrate our approach using soap bubbles and a feather. The soap bubbles illustrate Fresnel reflection, reveal the dynamics of the unseen flow field in which they travel, and display spherical harmonics in their undulations. Our single bubble simulation allows the user to directly interact with the flow field to influence the dynamics in real time. The free feather flutters and gyrates in response to lift and drag forces created by its motion relative to the flow. Vortices are created as the free feather falls in an otherwise quiescent flow. (Full paper, 4,853K)

Ray Tracing Height Fields
Huamin Qu, Feng Qiu, Nan Zhang, Arie kaufman, and Ming Wan
Proceeding of Computer Graphics International, pp. 202-209, 2003.

Abstract: We present a novel surface reconstruction algorithm which can directly reconstruct surfaces with different levels of smoothness in one framework from height fields using 3D discrete grid ray tracing. Our algorithm exploits the 2.5D nature of the elevation data and the regularity of the rectangular grid from which the height field surface is sampled. Based on this reconstruction method, we also develop a hybrid rendering method which has the features of both rasterization and ray tracing. This hybrid method is designed to take advantage of GPUs newly available flexibility and processing power. (Full paper, 180K)

Others:

Volume Rendering on Lattices
Feng Qiu
Thesis Proposal

GPU-based Visual Simulation of Dispersion in Urban Environments
Feng Qiu, Zhe Fan, Ye Zhao, Haik Lorenz, Jin Zhou, Arie Kaufman and Klaus Mueller, Poster, ACM/IEEE Super Computing 2006 Workshop on General-Purpose GPU Computing: Practice And Experience , 2006

GPU Accelerated Dispersion Simulation For Urban Security
Feng Qiu, Ye Zhao, Zhe Fan, Xiaoming Wei, Haik Lorenz, Jianning Wang, Suzanne Yoakum-Stover, Arie Kaufman, and Klaus Mueller
Proceeding of ACM Workshop on General Purpose Computing on Graphics Processors, 2004.

GPU Cluster for Scientific Computing and Large-Scale Simulation
Zhe Fan, Feng Qiu, Arie Kaufman, and Suzanne Yoakum-Stover
Proceeding of ACM Workshop on General Purpose Computing on Graphics Processors, 2004.

Hybrid Volumetric Ray-Casting
Wei Hong, Feng Qiu, Sarang Lakare, and Arie Kaufman
Proceeding of ACM Workshop on General Purpose Computing on Graphics Processors, 2004.

Hardware Accelerated Volume Rendering
Feng Qiu
Research Proficiency Examination report.