Magazine article National Forum

Interactive Computer Graphics for Understanding Science

Magazine article National Forum

Interactive Computer Graphics for Understanding Science

Article excerpt

The two most familiar uses of computer graphics are movies and video games. Movies generally need graphics that are indistinguishable from physical reality, whereas video games need graphics that can be generated quickly enough to be perceived as smooth motion. These two needs are incompatible, at least at the speeds of current computers. While the realistic computer graphics of movies have much greater emotional impact than the fast graphics of video games, the latter define a new interactive medium because their speed allows them to be computed in response to user actions. That is, they define two-way communications between users and computations. Users see graphical depictions of the numbers produced by computations and control those computations by moving a mouse or joystick. In video games, the subject matter of computations is generally characters chasing and shooting at each other. However, the subject matter could be anything. A less familiar use of computer graphics exists for interacting with scientific computations.

About 1988, computers became fast enough to generate 3D graphics at interactive speeds. This capability triggered a variety of new software systems for interacting with scientific computations, including general-purpose systems such as IBM's Data Explorer and Stellar Computer's Application Visualization System, and special purpose systems such as NASA's FAST for aerodynamic simulations and our own Vis5D for weather and other environmental simulations.

DEVELOPMENT OF Vis5D

Vis5D grew out of the longterm interest in weather graphics at the Space Science and Engineering Center (SSEC). In the early 1980s, we began experiments with 3-D graphics generated from all sorts of weather data, including observations from surface stations, balloons, aircraft and ships, images from satellites, radars and lidars (that is, a type of radar that employs lasers instead of microwaves), and the output of numerical weather models. These experiments led to two conclusions:

1. Three-dimensional weather graphics are useful only when they can be interactively rotated. 3-D graphics are inherently ambiguous because many points in the 3-D atmosphere are projected onto the same point on a 2-D display screen or on users' 2-D retinas. The most effective way to resolve this ambiguity is to allow users to rotate their viewpoint interactively, to change the mapping from 3-D to 2-D.

2. It is easier to make 3-D graphics from simulations than from observations, because of the errors and coverage gaps of observations and because of the greater variety of data-collection platforms and data organizations for observations.

Based on these conclusions, Vis5D was written in 1988 to generate interactive 3-D graphics from weather simulations. Users do not interact directly with the computations of weather models because they run too slowly to be visually interesting. Rather, users explore the large volumes of data left by weather models after such models finish, by interacting with the computations that convert that output data into 3-D images.

While the initial goal of interactive graphics was to provide the rotation necessary to resolve 3-D ambiguity, we exploited the interactive capability in many other ways to enable scientists to explore their data. Vis5D's users can interactively choose from a variety of ways of depicting temperature, pressure, humidity, and other atmospheric variables. These depictions may be quantitative and focused, such as planar-colored slices through data volumes, or qualitative and holistic, such as transparent colored "fogs" showing entire data volumes at once. Users also can interactively choose to view atmospheric state variables in various combinations to search for cause and effect relations among them, move forward and backward through time to trace physical events, and make and display computations such as the ratio of cloud water to total water.

The development of Vis5D was supported by NASA and EPA. …

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