Computer Graphics World

July 2009 34 n n n n Digital Imaging eight to 10 feet long, eight feet wide, and two feet high—which required a multitude of scans that had to be pieced together. "e white-light scans gave us detail down to a grain of sand," says Andersen. Indeed, the accuracy level of the scanner is for a configuration of one-thousandth of an inch. However, the biggest obstacles for this work had nothing to do with the equipment, but rather the subject and the environment, forcing Lichko to come up with an approach that suited this un- usual subject. First, the crew had to build a heavy-duty aluminum apparatus from which they positioned a 12-foot bar that spanned the beast. e scanner, which normally sits on a special tripod, was then attached to the bar and positioned as close to the specimen as possible. Second, the structure that housed Leonardo is next to a major railroad line and a fairly busy road with significant truck traffic. "Each time a train or a truck rumbled by, it would ruin the scan and I would have to start all over," says Lichko of the result- ing vibration. While Leonardo's surface appears fairly smooth, Lichko points out that there are many undercuts. "If you look at his head, for example, there is the eye socket, and you have to move [the scanner] several dif- ferent ways to capture the interior of that area," he explains. "e little rib bones sticking up, the vertebrae, are shaped like mushroom caps, and the scanner captures most of it, but then you need to move un- derneath to get it all—underneath, to the side, over the top, and so forth. ere are many little areas like that." As the scanner takes a series of pictures, the software Lichko wrote automatically processes the images into one 3D view. To accurately string the multiple images together into one, Lichko typically places photogrammetry dots on the object. "But we couldn't do that here, so Art [Ander- sen] and I worked hand in hand, whereby I would do a scan and then send it to Art sitting at a nearby computer so we knew the location from where the scan was tak- en, and using separate software, we fit each scan into place," he explains. Pieces of the Puzzle After a week, the group had nearly 26gb of 3D scan data to edit and piece together— far more than a typical industrial project would garner. Andersen notes that he uses existing technology to work with industrial clients, and then uses that same technology to study dinosaurs. "I'm just applying it in a different way," he says. Registering these high-fidelity scans with the required accuracy proved no easy task. Andersen and Lichko started at the center of the specimen and worked their way outward, to mini- mize the cumulative errors in a single direction. "If you start at the head and work your way to the tail, you build up errors, so the final scans may not line up like they should," explains Ander- sen. "When we were done with the final scan near Leonardo's foot, which is about five feet away from the starting point, the scans lined up perfectly with zero error." Lichko's scanner can output the entire polygon mesh, about 75mb (due to overlap- ping edges for aligning adjacent scans), or it can be done at 10 percent, resulting in a 7.5mb mesh in this case. With the latter op- tion, Andersen was able to properly orient the data, while Lichko scanned the subject. is enabled the two to identify areas of missing information, so those sections could be rescanned. Nevertheless, the mummy contains cracks and missing chunks here and there that result in missing data that cannot be acquired because the original A close-up look at the unique fossil. Images by Michael Berglund, Minnefex Inc. Picture courtesy Great Plains Dinosaur Museum and Field Station. (Above) Artist Mike Berglund had been hired to build a full-size family of Brachylophosaurs for a Leon- ardo exhibit. He sculpted the dino using LightWave for the base mesh and Zbrush for detailing, with the objective of milling the pieces. (Inset) He applied the X-ray images as displacement maps on highly subdivided planes in Zbrush, allowing him to rotate them and clarify the view of the liver-region scans.

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