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Cosmic Creation

Jun 1, 2007 12:00 PM, By Trevor Boyer

Computer graphics, cinematography, and display technologies mingle at the Gates Planetarium.

How do you depict a phenomenon that absorbs and distorts every photon of light that comes near it?

That would turn out to be the easy part, as the Denver Museum of Nature & Science (DMNS) undertook an ambitious production for its full-dome Gates Planetarium. Black Holes: The Other Side of Infinity premiered at the DMNS last year, showing off recent advances in both the visualization of black holes and the display capabilities of the museum's digital dome: Eleven Barco SLM R6 DLP projectors throw a single image onto a 65ft. domed screen.

Those 11 projectors share more than 10 million pixels: The image projected on the dome is a circle that's about 3,800 pixels in diameter. For modern 3D animation and graphics programs, filling a hemispherical frame that size is quite possible, and correct framing requires only that an animator/graphics artist understand where a typical viewer's eyes are focused.

But what if you want to incorporate live-action footage? How do you shoot that footage and then convert it to the planetarium's specialized video format, called Dome Master? And, returning to the original question, just how do you depict a black hole graphically in three dimensions over time?

Visualizing the invisible

By 2001, astrophysics professor Andrew Hamilton of the University of Colorado at Boulder had already been working on that question. In residence at the DMNS during a yearlong sabbatical, he'd been writing code for something called the Black Hole Flight Simulator, software for visualizing a physical trip into a black hole that was based on the equations of Einstein's theory of general relativity. The Black Holes project started in earnest when Thomas Lucas, an Ossining, N.Y.-based producer of documentaries for outlets such as PBS and the Discovery Channel, approached Hamilton with the news that NASA was willing to provide some funding for a planetarium show about black holes. (At that point, PBS's Nova became interested in developing a version of the show; Lucas eventually created a more interview-heavy version of the program in HD for Nova that aired last fall as “Monster of the Milky Way.”) Leveraging the funding from NASA, the DMNS successfully applied for a grant from the National Science Foundation for the remainder of the funding.

Most of the 23-minute Black Holes program — 41,360 frames at 30p — is computer-based visualization of real astrophysical phenomena. A virtual camera tracks from Earth to the center of the Milky Way in a dreamlike three-minute shot, passing accurate features such as gas clouds, star clusters, and spiral streamers along the way. A black hole is born from the death of a star as it goes supernova. “The key is to help the audience visualize what happened,” says Dan Neafus, the Gates Planetarium operations manager. “And then in doing that, you have to turn invisible wavelengths into something that you can see. We might as well turn it into something that's pretty.”

Much of the CGI content was produced by the National Center for Supercomputing Applications (NCSA), based at the University of Illinois at Urbana-Champaign. The NCSA's Advanced Visualization Laboratories has a mission to support the visualization efforts of science, and the center's task for Black Holes was to take the scientists' data and turn it into accurate, compelling visual sequences. Fortunately, its staff has an appropriate range of expertise. Donna Cox, head of the laboratories, is a professor of art; Bob Patterson came over from Industrial Light & Magic (ILM); and Stuart Levy specializes in the astronomical data and computer code.

The museum served as the hub of the production, taking in frame sequences from the NCSA and other sources. The four-person team at the DMNS, led by Neafus, tested them on the planetarium's screen, going back and forth with the providers of the content to perfect the colors, framing, and flow of the visualizations. “It's a very time-intensive process on all levels,” says Lucas, the director of Black Holes. “First of all, the scientists have to perfect their code for simulations. A lot of times, the code is breakthrough stuff. And then we ask them to go to a higher level with more time-steps and more detail. With the planetarium show that was especially difficult, because you have to fill a screen with 10 million pixels.”

Moving pixels

All those pixels required the NCSA to crunch through terabytes of data for the simulations. Fortunately, though, the test sequences averaged about 200MB for a draft shot, so the two teams could share frames easily via FTP. “Storage and throughput never became a major problem,” says Zachary Zager, system administrator for the planetarium and an animator on the Black Holes project. “Things kind of trickled in. So that allowed space between each [sequence] for us to process it, view it in the dome, and then get back to the people.” (Black Holes, which took about three years to complete, was a secondary project for almost everyone involved. The Denver team had to run the planetarium for the public during the day, and so most of its work on Black Holes happened at night after the museum closed.)

The Denver team used these draft sequences as a traditional producer would use rough cuts, Zager says.

Neafus' primary role on Black Holes was to determine whether the sequences actually worked in the dome on a detailed level. “How do we fine-tune it? Will it work with this scene? Is it too long, too short, too green, too high? Those kinds of things,” he says.

Lucas often came to Denver from New York to sit in the planetarium and evaluate the look and the flow of the show as it developed, and to oversee high-level editorial tasks such as the placement of narrator Liam Neeson's dialogue.

Zager was charged with maintaining the production system at the DMNS and specifying new hardware when it became necessary. Midway through the project, for example, the Denver team gradually decommissioned SGI Onyx 3800 boxes it had been using, and switched over to quad-core xw8400 workstations that HP provided. These systems run Adobe After Effects, Premiere Pro, and Autodesk Maya. Zager used Maya, for example, to create a sequence depicting Earth, and he created a layer of stars in After Effects. Zager finally used a fisheye lens within the Autodesk Mental Ray renderer to create a “dome-able” circular image, rendered out within a 4K-by-4K square to fit the requirements of the museum's Dome Master format.

At two points during production, the DMNS team purchased new RAID arrays to store the several iterations of each sequence and the final version of the program. The planetarium uses Quvis Qubit servers to play out the huge frames, which were saved as PNG files because of their support for alpha channels. Luckily for the museum, NCSA performed the terabyte-hungry final renders of the frames and then sent the final PNG files to Denver through the mail on several hard drives.

Film to dome

Not all of the frames of Black Holes started as scientific equations that were then represented by pixels. About two minutes of the program originated on 35mm film. This was novel for a planetarium show — most such programs contain no live-action sequences. This program was Lucas's first production for a planetarium, and he wanted to employ the usual kinetic elements of cinema — camera movement, frequent cuts, and live action itself — that are largely absent from full-dome planetarium productions. (Excessive action within immersive full-dome programs could cause disorientation — or, worse, induce motion sickness in audience members — so traditional productions have avoided fast camera movements and cutting.)

Black Holes features two location shoots. In Hawaii, the team used an Arriflex 435 Xtreme to shoot a trip to the peak of Mauna Kea, the location of the Keck observatory. There, physicist Andrea Ghez studies the orbits of the stars around the black hole at the center of the Milky Way. (She also created a sequence for Black Holes that depicted her subject of study.) At Cape Canaveral in Florida, with an Aaton 35-III, the team shot scientists' reaction to the launch of the NASA Swift satellite.

To suit the circular Dome Master format, both shoots required the use of a fisheye. A 6mm lens would have provided a full-circle fisheye, while an 8mm lens would expose more of the 35 frame horizontally — but with a cutoff at the top and the bottom. Lucas chose to use the 8mm lens because it offers more resolution. “So we had to tilt the image down and build out the top — the part that got cut off,” he says.

Framing was another challenge. The dome of the Gates Planetarium is tilted forward 25 degrees. Taking into account that tilt, and that audience members look relatively straight ahead, the DMNS team determined that the optimal way to shoot for the dome is to aim the camera lens 45 degrees above the horizon. That way the action is mostly in the bottom of any frame, where the audience is best able to view it.

In parts of the two live sequences, the camera was pointed too low, so the top of the image — corresponding to the vast back of the dome — did not extend far enough. There were also the cutoff portions of the fisheye to contend with. Both the DMNS team and post house Hannaway & Associates (Boulder, Colo.) created masks to extend the 35mm image across the full circle of the Dome Master frame.

Hannaway performed a 4K scan of the 35mm film using an Academy Award-winning digital film scanner built by Ray Feeney of RFX in Hollywood. According to Wyndham Hannaway, principal at the post house, other 4K scanners would have scanned the useless black (left and right) portions of the frames using 4,000 horizontal lines, and would have thrown out much of the vertical resolution of the circular image. “Our scanner adjusts closer and further from the film,” Hannaway says, “so we can put our 4,000 lines right across that circle. Based on that we're able to deliver 4000×4000 to the museum.”

Final stages

The scanner output 16-bit RGB files, which were converted to 10-bit Cineon files. Michael Lauter, cinema technologist at Hannaway, morphed the Cineon frames in Autodesk Flame to better fill the circular Dome Master format. These files were handed off to DMNS as TIFFs. Matthew Brownell at DMNS performed the remaining painting tasks in After Effects — extending a blue sky, for instance.

The final program, including the audio sync, was edited at the museum in Premiere Pro. Neafus says that despite the massive frame sizes, the processing power of the HP workstations didn't cause editing bottlenecks. Instead, slowdowns occurred while getting frames on and off the workstations from the central server. “We spent a lot of time upgrading the path to our big servers in the museum,” he says. “They deal with terabytes of storage, so there's a lot of time back and forth to make that work. It's kinda node by node and changes step by step. We're not quite at Fibre yet.”

In the dome of the Gates Planetarium, the 11 projectors are fed sections of the Dome Master frames from the Qubit servers. DMNS uses a combination of freeware and commercial software to correctly section the frames. “You basically slice that circle out and come up with a camera view for each of the projectors,” Neafus says. “It's a pretty specific algorithm. Dome Master has some definitions about how it handles the fisheye image. It's an equidistant azimuthal fisheye kind of thing. So there's a specific math definition for how that flat, circular, 2D image translates to the dome.”

The program about black holes — themselves great cosmic distorters — is then distorted on the hemispherical screen to immerse the viewer.

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