We propose a new computation model for simulating elastic thin shells at interactive rates. Existing graphical simulation methods are mostly based on dihedral angle energy functions, which need to compute the first order and second order partial derivatives with respect to current vertex positions as bending forces and stiffness matrices. The symbolic derivatives are complicated in nonisometric element deformations. To simplify computing the derivatives, instead of directly constructing the dihedral angle energy, we use the orientation change energy of mesh edges. A continuum-mechanics-based orientation-preserving rod element model is developed to provide the bending forces. The advantage of our method is simple bending force and stiffness matrix computation, since in the rod model, we apply a novel incremental construction of the deformation gradient tensor to linearize both tensile and orientation deformations. Consequently, our model is efficient, easy to implement, and supports both quadrilateral and triangle meshes. It also treats shells and plates uniformly.

In this paper, we introduce a novel application of volume modeling techniques on laser Benign Prostatic Hyperplasia (BPH) therapy simulation. The core technique in our system is an algorithm for simulating the tissue vaporization process by laser heating. Different from classical volume CSG operations, our technique takes experimental data as the guidance to determine the vaporization amount so that only a specified amount of tissue is vaporized in each time. Our algorithm uses a predictor-corrector strategy. First, we apply the classical CSG algorithm on a tetrahedral grid based distance field to estimate the vaporized tissue amount. Then, a volume-correction phase is applied on the distance field. To improve the performance, we further propose optimization approaches for efficient implementation.

We propose point with implicit connectivity (PIC) as a new data structure for representing solid objects using points. In the PIC representation, an object is adaptively sampled into an octree, where each leaf cell contains at most one surface component of the object. Each surface component is represented by a vertex, together with inside/outside classification values of the cell corners. PIC objects are compact, feature-preserving, and supports easy construction of the boundary surfaces. To convert geometric objects into the PIC representation, we propose a sampling algorithm and use quadric error functions as error metrics. For CSG operations between PIC objects, we present a feature-preserving, adaptive CSG algorithm on the octrees. Our experiments show promising results for PIC objects with sharp features and large flat regions.

We present a fast, topology-preserving approach for isosurface simplification. The underlying concept behind our approach is to preserve the disconnected surface components in cells during isosurface simplification. We represent isosurface components in a novel representation, called enhanced cell, where each surface component in a cell is represented by a vertex and its connectivity information. A topology-preserving vertex clustering algorithm is applied to build a vertex octree. An enhanced dual contouring algorithm is applied to extract error-bounded multiresolution isosurfaces from the vertex octree while preserving the finest resolution isosurface topology. Cells containing multiple vertices are properly handled during contouring. Our approach demonstrates better results than existing octree-based simplification techniques.

We present an efficient stereoscopic rendering algorithm supporting interactive navigation through large-scale 3D voxel-based environments. In this algorithm, most of the pixel values of the right image are derived from the left image by a fast 3D warping based on a specific stereoscopic projection geometry. An accelerated volumetric ray casting then fills the remaining gaps in the warped right image. Our algorithm has been parallelized on a multiprocessor by employing effective task partitioning schemes and achieved a high cache coherency and load balancing. We also extend our stereoscopic rendering to include view-dependent shading and transparency effects. We have applied our algorithm in two virtual navigation systems, flythrough over terrain and virtual colonoscopy, and reached interactive stereoscopic rendering rates of more than 10 frames per second on a 16-processor SGI Challenge.

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.

Presents an interactive stereoscopic rendering algorithm of voxel-based terrain. It provides unambiguous depth information of a terrain scene by generating perspective images for a pair of eyes with a horizontal parallax. The left-eye image is generated using a fast ray-casting algorithm accelerated by exploiting a specific ray coherence method in the voxel-based terrain scene. The right-eye image is obtained by exploiting the frame coherence between the two views. Most of the pixel values are directly obtained from the left image by re-projection. The remaining pixels are computed by ray casting, which is further accelerated with ray coherence. An A-buffer is employed to reduce the image error caused by re-projection to non-integer pixel locations. Image-based task partitioning schemes are explored to effectively parallelize our algorithm on a multiprocessor.