Flow volumes are extended for use in unsteady (time-dependent) flows. The resulting unsteady flow volumes are the 3D analogs of streaklines. There are few examples where methods other than particle tracing have been used to visualize time-varying flows. Since particle paths can become convoluted in time, there are additional considerations to be made when extending any visualization technique to unsteady flows. We present some solutions to the problems which occur in subdivision, rendering and system design. We apply the unsteady flow volumes to a variety of field types, including moving multi-zoned curvilinear grids.

Simulation of complex 3-dimensional phenomena generate data sets which are hard to comprehend using conventional 2-dimensionally oriented visualization tools. One way to overcome this limitation is to employ various volume visualization techniques. While early volume visualization techniques worked well on simple scalar volumes they failed to exploit frame buffer hardware capabilities and handle higher order data such as vector fields. Work at Lawrence Livermore National Laboratory has centered on developing new techniques and extending existing techniques. This paper describes the various algorithms developed for volume rendering, and presents new methods of examining vector fields in a volumetric fashion.

A method is described for switching smoothly between rendering algorithms as required by the amount of visible surface detail. The result will be more realism with less computation for displaying objects whose surface detail can be described by one or more bump maps. The three rendering algorithms considered are a BRDF, bump mapping, and displacement mapping. The bump mapping has been modified to make it consistent with the other two. For a given viewpoint, one of these algorithms will show a better trade-off between quality, computation time, and aliasing than the other two. The decision as to which algorithm is appropriate is a function of distance, viewing angle, and the frequency of bumps in the bump map.

Flow volumes are the volumetric equivalent of stream lines. They provide more information about the vector field being visualized than do stream lines or ribbons. Presented is an efficient method for producing flow volumes, composed of transparently rendered tetrahedra, for use in an interactive system. The problems of rendering, subdivision, sorting, composing artifacts, and user interaction are dealt with. Efficiency comes from rendering only the volume of the smoke, and using hardware texturing and compositing.>