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Cosmic Voyage, a new IMAX film scheduled to debut at the Smithsonian National Air and Space Museum in August, is typical of IMAX films in the feeling of sensory immersion it creates in its viewers. But the technology of its production is unique. |
A sweeping journey through space and time, the
film carries viewers from the largest structures in
the known universe down to subatomic quarks; from the
first few seconds after the big bang to the present
day.
Cosmic Voyage is one of the first IMAX films to use
supercomputing simulations and the first IMAX film
ever to use four minutes of research-quality
scientific visualization. The four-minute segment,
which begins shortly after the big bang, shows the
expansion of the universe, the gravitational collapse
of structure and the formation of galaxies, and the
collision of two spiral galaxies. It was a result of
the collaborative efforts of NCSA scientific
visualization experts, scientists in the Grand
Challenge Cosmology Consortium (GC3), two movie
production companies, and numerous high-performance
computing machines at multiple centers. While the
film's primary goal is to entertain and educate, those
four minutes yielded unexpected scientific insights
and spurred the development of new scientific
visualization technology.
At the heart of the collaboration is Donna Cox, UIUC professor of art and design and principal investigator of NCSA's Renaissance Experimental Laboratory. Cox, the associate producer for scientific visualization for Cosmic Voyage and the art director for the four-minute simulation segment, was involved in every step of the film's production -- from the conceptual and fund-raising stage to consulting on the finishing touches.
This scene uses an algorithm (written by Greg Bryan, a graduate student working in the laboratory of UIUC Astronomy Professor and NCSA Senior Research Scientist Michael Norman) based on the Harrison- Zel'dovich spectrum describing the density fluctuations in the early universe. Pixar, the movie production company famous for creating Toy Story, ran the simulation and created the visualization for this sequence.
The first scene segues into the hierarchical collapse of structure, starting with a large-scale overview showing the early formation of web-like filaments, then traveling along a filament to show the formation of galaxies along knots in the filaments. The scene concludes with a cluster of galaxies forming at the intersection of filaments.
This scene, which lasts 70 seconds, is based on a simulation run by Frank Summers, a postdoctoral researcher in astronomy at Princeton University and member of the GC3. The simulation follows the evolution of 2.1 million dark matter particles and 2.1 million gas particles. Pixar, which was consumed with Toy Story, lacked the disk space, the networks, the human resources, and the computing power to deal with this and the following simulation. "This project moved from a Hollywood production to a major supercomputer/mass storage challenge," says Cox, who assumed responsibility for coordinating the simulations and visualizations for the subsequent scenes. "NCSA's POWER CHALLENGEarray, high-speed networks, and mass storage provided the resources to tackle the challenge."
Each IMAX motion-picture frame is about 10 times the area of a standard frame of 35-millimeter (mm) film. Because of this, creating images for the giant IMAX screen demands simulations of unprecedented resolution. In Summers' case the resolution had to be 10 times greater than anything he had done previously. In turn NCSA produced extremely high-resolution images from the data, at 4,096 x 3,002 pixels.
NCSA allowed Summers to use one of its (then) new SGI POWER CHALLENGE machines to run the calculations. "I basically ran it full out, using all eight processors, for a solid month," says Summers. The result: 120 gigabytes of remarkable data. "A cluster of galaxies has internal gas," explains Summers. "When a galaxy, composed of both gas and stars, falls into a cluster, the hot gas [of the cluster] interacts with and strips the gas from the galaxy -- something we call RAM-pressure stripping. When I looked at the data, the amount of RAM-pressure stripping was much greater than I had previously suspected. There were long streamers of gas trailing behind these galaxies that had fallen into the cluster."
The final 1 minute and 50 seconds of the sequence -- the collision and the merging of two spiral galaxies-is based on a simulation carried out by Chris Mihos and Lars Hernquist of the University of California, Santa Cruz, on San Diego Supercomputer Center's CRAY C90 system. (Mihos is now a Hubble Fellow at Johns Hopkins University.) The scientists modeled the gravitational interplay of 250,000 particles representing galaxies by making local estimates of the pressure, density, and temperature of interstellar gas.
Achieving the exact degree of resolution required 750 CPU hours to compute and generated 65 gigabytes of raw data that were then transferred to NCSA for visualization. As the galaxies merge and then draw apart, tidal forces and galactic rotation cause the galaxies to cast off stars and gas in the form of long, thin "tidal tails." The compression of interstellar gas into the merged galaxies fuels an intense burst of star formation. Like Summers, Mihos and Hernquist found that increasing the resolution of their simulation led to new science, ". . . particularly," said Mihos, "the large number of small, condensing gas clouds in the colliding galaxies that could be related to the formation of young, luminous star clusters or small dwarf galaxies, which are seen in many observed galaxy collisions."
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Images from a galaxy- collision sequence in the Smithsonian's IMAX movie. The galaxies merge over a billion years to form a single massive structure. |
To create the camera moves through the simulations, Cox worked with Patterson, the choreographer of the sequence, and Marcus Thiebaux, the virtual environment research programmer at UIC's Electronic Visualization Laboratory, to create a voice-driven CAVE application called the Virtual Director, a virtual reality method for directing the computer graphics camera for real-time playback or animation recording. The team made numerous videotapes, aiming for just the right trajectory here or the most revealing angle there.
Finally the choreographed and rendered images were sent to Santa Barbara Studios in California where they were recorded to 70 mm IMAX film. Santa Barbara Studios also created another 10 minutes of special effects, scientific illustrations (including a "snapshot" of one of Norman's simulations illustrating large-scale structure), and Jet Propulsion Laboratory-mapped data. "Fourteen minutes of 4,096 x 3,002 pixels-per-frame, high-resolution IMAX computer graphics is unheard of in the industry," says Cox.
"There were many meetings at the Smithsonian to get everything approved," notes Cox. "The Smithsonian's Science Advisory Committee -- including a number of Nobel Laureates and other science experts including GC3 members -- scrutinized each segment."
Following its premiere at the Smithsonian Air and Space Museum this summer, Cosmic Voyage will travel to over 150 IMAX and OMNIMAX theaters around the world.
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NCSA: The National Center for Supercomputing
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