Computer Graphics World

July 2009 35 Digital Imaging n n n n source is missing. For these areas, Andersen had to fill in the data by hand, creating it us- ing Raindrop Geomagic's software. Using PolyWorks' reverse engineering software and Imageware's Surfacer, an older surfacing program now owned by Siemens, Andersen began the meticulous process of assembling all 300-plus scans, each of which had to align perfectly, before being resolved to within .5mm. "We needed a lot of computer power to do a project like this," Andersen points out. More, in fact, than was available on site in Malta. ere- fore, when he had to generate the full-size, high-resolution digital model that would be necessary for rapid prototyping, Ander- sen was forced to digitally divide the single, blended mesh into eight sections (head, neck, chest, and so forth). To expedite the model assembly prior to rapid prototyping, Andersen also created virtual dowels in the Surfacer software. Fi- nally, he had to generate an STL file (which was nearly half a gigabyte in size) for the 3D printing process. Indeed, the 3D scan was necessary for prototyping. But, it also provided a 3D volume of Leonardo, which offers a more in-depth look at a subject's anatomy than can be had from a 2D image. "With this project, we learned we can now create a very accurate model cast without ever touching the surface of the specimen. It can be a 100 percent nondestructive pro- cess," says Andersen. "It also gives credence to the possibility of scanning very fragile ob- jects that could never have been scanned in the past through simple modeling and cast- ing." For example, law enforcement could make casts of footprints in the snow at crime scenes. is kind of technology, An- dersen adds, also holds potential in proving product liability and patent infringement, as well as for digital inspection of engineered parts and even filmmaking through the ac- curate reproduction of props. 'Cloning' Leonardo RP is hardly new—it's been used for years to produce accurate physical replicas of parts in the auto industry and even sculp- tures by artists, all from 3D computer files. In this application, however, the subject—a dinosaur—proved too large for most facili- ties. at's when Martin Jones from Ford Motor Co. unearthed a solution. Jones took the full-resolution data gar- nered from the white-light scan process and fed the information into the compa- ny's prototyping machine, but the output still had to be done in chunks (based on the eight segments Andersen made of the scanned data) due to their dinosaur-size proportions. Later, those blocks were shipped to the Black Hills Institute for assembly. "We put the pieces together and then molded them as a unit," says the Black Hills Institute's Larson, who was invited to join the project by Murphy. A laser so- lidified the plastic material that was used to output the prototyped model. "e material (a photopolymer) they used in the cast was brittle, so we had to be very careful. ere were a few slight offsets we had to compensate for in the data; with something like this, you cannot get it ab- solutely perfect," Larson says. "ere was a mesh going across the entire surface of the fossil, so you are going 10 feet across from one registration end to the other; in some cases, there was a bit of discrepancy, maybe one-tenth of an inch, where we would have to build up a little clay to make a bridge so you wouldn't see the seams." Unfortunately, the digital volume was not complete, as the group was unable to scan the downside (the side the dinosaur was lying on when he died) due to the vi- sual obstructions resulting from the steel structure and the plaster jacket that had been supporting Leonardo since he was excavated. Because rapid prototyping re- quires a solid output, the information has to be present in the computer file. Ander- sen fixed this problem by meticulously adding a base and sides to the data prior to the parts being prototyped. According to Larson, creating a RP clone of the dinosaur enables scientists and paleon- tologists to be more hands-on while study- ing it, since the original fossil is much too delicate to touch—and much too valuable to become extinct right before their eyes. "When you look at Leonardo, he is a mottled color, sandstone, and when you bring a scan in, it typically is an artificial color of some sort. You can see more fea- tures in the artificial color, and things pop more, like the tendons in his back and the skin impressions," says Cubic Vision's Lichko. "He is amazing and unique." X-rays were used to examine Leonardo's insides. This enhanced X-ray image provides a look to the dinosaur's gut (the pebble-shaped matter is gut content).

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