Caixia Zhang - Academia.edu (original) (raw)

Papers by Caixia Zhang

Fourth International Workshop on Volume Graphics, 2005., 2005

In this paper, we examine the performance of the early z-culling feature on current high-end comm... more In this paper, we examine the performance of the early z-culling feature on current high-end commodity graphics cards and present an isosurface-aided hardware acceleration algorithm for slice-based volume rendering (iSBVR) to maximize its utilization. We analyze the computational models for early z-culling of the texture based volume rendering. We demonstrate that the performance improves with two to four times speedup against an original straightforward SBVR on an ATI 9800 pro display board. As volumetric shaders become increasingly complex, the advantages of fast z-culling will become even more pronounced.

International 2005 Computer Graphics, 2005

Some applications require scenes mixing polygonal and volumetric objects and shadows make the sce... more Some applications require scenes mixing polygonal and volumetric objects and shadows make the scenes more realistic. This paper describes a shadow algorithm for mixed polygonal and volumetric data, including the generation of soft shadows for area light sources. Our volume shader leverages advanced graphics GPU for an accelerated and feasible solution. The shadow and soft shadow algorithm applies to all combinations of volumes and polygons, without any restriction on the geometric positioning and overlap of the volumes and polygons. For realistic rendering where we have a high albedo participating media, multiple scattering is significant. We extend our algorithm to handle both multiple forward scattering and back scattering with light attenuation. This constitutes a complete system for shadow generation and light propagation.

2004 IEEE Symposium on Volume Visualization and Graphics

Direct volume rendering has seen many improvements since its inception fifteen years ago. In this... more Direct volume rendering has seen many improvements since its inception fifteen years ago. In this paper, we segment the volume into geometrically disjoint regions that can be rendered to provide a more effective and interactive volume rendering of structured and unstructured grids. Our segmentation is based upon intervals within the scalar field, producing a set of geometrically defined interval volumes. We present many advantageous properties in using interval volumes, and provide several new rendering operations or shaders to provide effective visualizations of the 3D scalar field. In particular, we demonstrate new technologies that allow interval volumes to be rendered interactively and/or used to reduce the amount of rasterization or rendering primitives in a volume renderer. We illustrate the use of interval volumes to highlight contour boundaries or material interfaces. Several surface shaders that can easily be integrated in the volume renderer are presented. To construct the interval volumes, we cast the problem one dimension higher, using a higher-dimensional isosurface construction for interactive computation or segmentation. The algorithm is independent of the dimension and topology of the polyhedral cells comprising the grid, and thus offers an excellent enhancement to the volume rendering of unstructured grids. We present examples using hexahedral and tetrahedral cells from time-varying and multi-attribute datasets.

Fourth International Workshop on Volume Graphics, 2005., 2005

In this paper, we study the interval segmentation and direct rendering of time-varying volumetric... more In this paper, we study the interval segmentation and direct rendering of time-varying volumetric data to provide a more effective and interactive volume rendering of time-varying structured and unstructured grids. Our segmentation is based upon intervals within the scalar field between time steps, producing a set of geometrically defined time-varying interval volumes. To construct the time-varying interval volumes, we cast the problem one dimension higher, using a five-dimensional iso-contour construction for interactive computation or segmentation. The key point of this paper is how to render the time-varying interval volumes directly. We directly render the 4D interval volumes by projecting the 4D simplices onto 3D, decomposing the projected 4-simplices to 3-simplices and then rendering them using a modified hardware-implemented projected tetrahedron method. In this way, we can see how interval volumes change with the time in one view. The algorithm is independent of the topology of the polyhedral cells comprising the grid, and thus offers an excellent enhancement to the volume rendering of time-varying unstructured grids. Another advantage of this algorithm is that various volumetric and surface boundaries can be embedded into the time-varying interval volumes.

IEEE Visualization 2004

Traditional flow volumes construct an explicit geometrical or parametrical representation from th... more Traditional flow volumes construct an explicit geometrical or parametrical representation from the vector field. The geometry is updated interactively and then rendered using an unstructured volume rendering technique. Unless a detailed refinement of the flow volume is specified for the interior, information inside the underlying flow volume is lost in the linear interpolation. These disadvantages can be avoided and/or alleviated using an implicit flow model. An implicit flow is a scalar field constructed such that any point in the field is associated with a termination surface using an advection operator on the flow. We present two techniques, a slice-based three-dimensional texture mapping and an interval volume segmentation coupled with a tetrahedron projection-based renderer, to render implicit stream flows. In the first method, the implicit flow representation is loaded as a 3D texture and manipulated using a dynamic texture operation that allows the flow to be investigated interactively. In our second method, a geometric flow volume is extracted from the implicit flow using a high dimensional iso-contouring or interval volume routine. This provides a very detailed flow volume or set of flow volumes that can easily change topology, while retaining accurate characteristics within the flow volume. The advantages and disadvantages of these two techniques are compared with traditional explicit flow volumes.

IEEE Transactions on Visualization and Computer Graphics, 2003

This paper describes an efficient algorithm to model the light attenuation due to a participating... more This paper describes an efficient algorithm to model the light attenuation due to a participating media with low albedo. Here, we consider the light attenuation along a ray, as well as the light attenuation emanating from a surface. The light attenuation is modeled using a splatting volume renderer for both the viewer and the light source. During the rendering, a 2D shadow buffer accumulates the light attenuation. We first summarize the basic shadow algorithm using splatting [30]. Then an extension of the basic shadow algorithm for projective textured light sources is described. The main part of this paper is an analytic soft shadow algorithm based on convolution techniques. We describe and discuss the soft shadow algorithm, and generate soft shadows, including umbra and penumbra, for extended light sources.

Visualization, 2002. VIS 2002. IEEE, 2002

Fourth International Workshop on Volume Graphics, 2005., 2005

In this paper, we study the interval segmentation and direct rendering of time-varying volumetric... more In this paper, we study the interval segmentation and direct rendering of time-varying volumetric data to provide a more effective and interactive volume rendering of time-varying structured and unstructured grids. Our segmentation is based upon intervals within the scalar field between time steps, producing a set of geometrically defined time-varying interval volumes. To construct the time-varying interval volumes, we cast the problem one dimension higher, using a five-dimensional iso-contour construction for interactive computation or segmentation.

Fourth International Workshop on Volume Graphics, 2005., 2005

In this paper, we examine the performance of the early z-culling feature on current high-end comm... more In this paper, we examine the performance of the early z-culling feature on current high-end commodity graphics cards and present an isosurface-aided hardware acceleration algorithm for slice-based volume rendering (iSBVR) to maximize its utilization. We analyze the computational models for early z-culling of the texture based volume rendering. We demonstrate that the performance improves with two to four times speedup against an original straightforward SBVR on an ATI 9800 pro display board. As volumetric shaders become increasingly complex, the advantages of fast z-culling will become even more pronounced.

International 2005 Computer Graphics, 2005

Some applications require scenes mixing polygonal and volumetric objects and shadows make the sce... more Some applications require scenes mixing polygonal and volumetric objects and shadows make the scenes more realistic. This paper describes a shadow algorithm for mixed polygonal and volumetric data, including the generation of soft shadows for area light sources. Our volume shader leverages advanced graphics GPU for an accelerated and feasible solution. The shadow and soft shadow algorithm applies to all combinations of volumes and polygons, without any restriction on the geometric positioning and overlap of the volumes and polygons. For realistic rendering where we have a high albedo participating media, multiple scattering is significant. We extend our algorithm to handle both multiple forward scattering and back scattering with light attenuation. This constitutes a complete system for shadow generation and light propagation.

2004 IEEE Symposium on Volume Visualization and Graphics

Direct volume rendering has seen many improvements since its inception fifteen years ago. In this... more Direct volume rendering has seen many improvements since its inception fifteen years ago. In this paper, we segment the volume into geometrically disjoint regions that can be rendered to provide a more effective and interactive volume rendering of structured and unstructured grids. Our segmentation is based upon intervals within the scalar field, producing a set of geometrically defined interval volumes. We present many advantageous properties in using interval volumes, and provide several new rendering operations or shaders to provide effective visualizations of the 3D scalar field. In particular, we demonstrate new technologies that allow interval volumes to be rendered interactively and/or used to reduce the amount of rasterization or rendering primitives in a volume renderer. We illustrate the use of interval volumes to highlight contour boundaries or material interfaces. Several surface shaders that can easily be integrated in the volume renderer are presented. To construct the interval volumes, we cast the problem one dimension higher, using a higher-dimensional isosurface construction for interactive computation or segmentation. The algorithm is independent of the dimension and topology of the polyhedral cells comprising the grid, and thus offers an excellent enhancement to the volume rendering of unstructured grids. We present examples using hexahedral and tetrahedral cells from time-varying and multi-attribute datasets.

Fourth International Workshop on Volume Graphics, 2005., 2005

In this paper, we study the interval segmentation and direct rendering of time-varying volumetric... more In this paper, we study the interval segmentation and direct rendering of time-varying volumetric data to provide a more effective and interactive volume rendering of time-varying structured and unstructured grids. Our segmentation is based upon intervals within the scalar field between time steps, producing a set of geometrically defined time-varying interval volumes. To construct the time-varying interval volumes, we cast the problem one dimension higher, using a five-dimensional iso-contour construction for interactive computation or segmentation. The key point of this paper is how to render the time-varying interval volumes directly. We directly render the 4D interval volumes by projecting the 4D simplices onto 3D, decomposing the projected 4-simplices to 3-simplices and then rendering them using a modified hardware-implemented projected tetrahedron method. In this way, we can see how interval volumes change with the time in one view. The algorithm is independent of the topology of the polyhedral cells comprising the grid, and thus offers an excellent enhancement to the volume rendering of time-varying unstructured grids. Another advantage of this algorithm is that various volumetric and surface boundaries can be embedded into the time-varying interval volumes.

IEEE Visualization 2004

Traditional flow volumes construct an explicit geometrical or parametrical representation from th... more Traditional flow volumes construct an explicit geometrical or parametrical representation from the vector field. The geometry is updated interactively and then rendered using an unstructured volume rendering technique. Unless a detailed refinement of the flow volume is specified for the interior, information inside the underlying flow volume is lost in the linear interpolation. These disadvantages can be avoided and/or alleviated using an implicit flow model. An implicit flow is a scalar field constructed such that any point in the field is associated with a termination surface using an advection operator on the flow. We present two techniques, a slice-based three-dimensional texture mapping and an interval volume segmentation coupled with a tetrahedron projection-based renderer, to render implicit stream flows. In the first method, the implicit flow representation is loaded as a 3D texture and manipulated using a dynamic texture operation that allows the flow to be investigated interactively. In our second method, a geometric flow volume is extracted from the implicit flow using a high dimensional iso-contouring or interval volume routine. This provides a very detailed flow volume or set of flow volumes that can easily change topology, while retaining accurate characteristics within the flow volume. The advantages and disadvantages of these two techniques are compared with traditional explicit flow volumes.

IEEE Transactions on Visualization and Computer Graphics, 2003

This paper describes an efficient algorithm to model the light attenuation due to a participating... more This paper describes an efficient algorithm to model the light attenuation due to a participating media with low albedo. Here, we consider the light attenuation along a ray, as well as the light attenuation emanating from a surface. The light attenuation is modeled using a splatting volume renderer for both the viewer and the light source. During the rendering, a 2D shadow buffer accumulates the light attenuation. We first summarize the basic shadow algorithm using splatting [30]. Then an extension of the basic shadow algorithm for projective textured light sources is described. The main part of this paper is an analytic soft shadow algorithm based on convolution techniques. We describe and discuss the soft shadow algorithm, and generate soft shadows, including umbra and penumbra, for extended light sources.

Visualization, 2002. VIS 2002. IEEE, 2002

Fourth International Workshop on Volume Graphics, 2005., 2005

In this paper, we study the interval segmentation and direct rendering of time-varying volumetric... more In this paper, we study the interval segmentation and direct rendering of time-varying volumetric data to provide a more effective and interactive volume rendering of time-varying structured and unstructured grids. Our segmentation is based upon intervals within the scalar field between time steps, producing a set of geometrically defined time-varying interval volumes. To construct the time-varying interval volumes, we cast the problem one dimension higher, using a five-dimensional iso-contour construction for interactive computation or segmentation.