An Extended Volume Visualization System for Arbitrary Parallel Projection

We present a special architecture for arbitrary parallel projection for visualization of volumetric data. Using a ray-casting technique, parallel memory access, and pipelined processing of rays in a composition tree, we can achieve interactive rendering rates for a 512 dataset. 1.1 The Cube Architecture Cube is a special-purpose computer architecture for volume visualization [1]. The heart of the architecture is a Cubic Frame Bu er (CFB), which is a large (e.g., 128M voxels for a 512 CFB) three-dimensional memory of voxels. The voxel is a quantum unit of volume, which has a value representing some measurable properties of the real object or phenomenon, such as the color, uorescent level, material, and translucency ratio. Cube's processing speed is achieved by handling beams of voxels rather than single voxels. In order to access a full beam of voxels simultaneously, a 3D modular organization of the CFB has been designed [1]. The special 3D skewed organization of the CFB enables con ict-free access to a full beam (axial ray) of n voxels, in any orthographic direction. The 3D Viewing Processor (VP3) [2] generates 2D shaded orthographic projections of the CFB images. It casts rays into the CFB in the speci ed viewing direction, utilizes the CFB parallel memory organization for con ict-free retrieval of a beam and then determines the pixel projection along that beam. It employs a sequence of n processing units which team up to generate the projection along a beam of n voxels in O(log n) time for a CFB of n voxels. Consequently, the time necessary to generate an orthographic projection of n pixels is only O(nlog n), rather than the conventional O(n) time. The VP3 also shades the projected pixels concurrently with the projection stage by employing the depth-gradient congradient shading technique [3]. Arbitrary parallel projections are currently created by rst rotating the scene and then viewing it through a principal orthographic direction. However, the CFB image is distorted every time a rotation is executed. A major goal of the extended Cube architecture project, presented in this paper, is to develop and prototype an alternative mechanism for parallel viewing that supports real-time arbitrary viewing.