Sen - R 9715 1997

The design and implementation of an interactive spot noise algorithm is presented. Spot noise is a technique which utilizes texture for the visualization of ow elds. Various design tradeoos are discussed that allow an optimal implementation on a range of high end graphical workstations. Two applications are given: the steering of a smog prediction simulation and browsing a very large data set resulting from a direct numerical simulation of turbulence. These applications provide the motivation for the need of interactive visualization techniques. 1. INTRODUCTION. During the last decade the need for flow visualization techniques for representing vector fields has grown substantially. The reason for this is that increasingly complex phenomena are simulated and that the resulting data sets are becoming more difficult to interpret. The visualization community has developed many accurate and robust flow visualization methods to display these data sets [1]. Simultaneously, there is also a growing demand for interactive computing in which users can control various aspects of the application [2]. The role of computational steering and browsing of very large scientific data bases are two examples of this demand. Both examples require highly interactive visualization to accommodate the requirements for adequate animation and feedback rates. Spot noise is a texture synthesis technique which can be used to visualize flow fields [3]. Rather than mapping the underlying vector field to produce colored geometric objects, spot noise uses texture. The primary advantage over other flow visualization techniques is that texture can give a continuous view of a 2D field opposed to visualization at only discrete positions, as with arrow plots or streamlines. The basic idea is that if many particles are used to represent the flow, the individual particles can no longer be discerned and texture is perceived instead. Spot noise generates texture by adding a large number of randomly positioned spots with a random intensity. A spot is defined to be any geometric shape, but usually a small circle is used. Properties of the spot directly control the properties of the texture. Therefore, by modifying the shape of the spot as a function of the data, the data are visualized by texture. The downside of spot noise is that it is very computationally expensive. A large number of particle paths and particle positions must be calculated, spots must be transformed, scan converted, textured and blended. Previously, spot noise textures were generated as a preprocessing step and the resulting …