Time Management, Simultaneity and Time-Critical ... - CiteSeerX

Time Management, Simultaneity and Time-Critical Computation in Interactive Unsteady Visualization Environments Steve Bryson MRJ, Inc./NASA Ames Research Center Sandy Johan NASA Ames Research Center

Abstract This paper describes time management and time critical computing for a near-real-time interactive unsteady visualization environment. Subtle issues regarding the flow of time are described, formalized and addressed. The resulting system correctly reflects time behavior while allowing the user to control the flow of time. The problem of time-critical computation is discussed, and a solution is presented. These time-critical algorithms provide control over the frame rate of a visualization system, allowing interactive exploration.

1 Introduction Unsteady, or time-varying, simulations are becoming increasingly common in computational science. Examples abound in computational fluid dynamics (CFD) and computational magnetohydrodynamics (MHD)among other fields. These simulations typically involve extremely complex phenomena, reflecting spatial and temporal behaviors. The purpose of these simulations is typically to provide insight into these phenomena. For this paper, we are assuming that the unsteady behavior is represented as a series of discrete timesteps of data. Visualization provides a significant contribution to this insight. Several new challenges arise in the visualization of unsteady data sets. One of these challenges is to provide to the researcher performing the simulation the means to explore that simulation. Near-real-time interactive directmanipulation techniques (which we will refer to as “directmanipulation) are one approach to the problem of simulation complexity. Direct manipulation techniques allow the researcher to move a visualization to a desired location and view that visualization after a short delay, resulting in the effect of exploring the simulation data. While the delay between a user control motion and the display of a resulting visualization is best kept less than 0.2 seconds, experience has shown that delays in the display of the visualization of up to 0.5 seconds for the visualization are tolerable in a direct manipulation context. Direct manipulation allows the

researcher to quickly explore a data set, identifying phenomena of interest. The most fully developed use of direct manipulation is in virtual-reality based visualization systems such as the virtual windtunnel. To be effective, direct manipulation requires that the user have some immediate (