Issue link: https://digital.copcomm.com/i/14320
Scanning n n n n Department (CPD), which had recently pur- chased a large-format Leica area laser scanner. Tey will be using the device for crime and accident investigations to reconstruct scenes in 3D. Andersen contacted Herb Keeler, the person in charge of the police scanning, and asked if they would be interested in working on Chicago’s own T. rex. Te department de- cided that scanning the mount would be a good training exercise and that it could gener- ate great publicity for the CPD. Last fall, the CPD arrived at the Field Muse- um with the scanner, accessory items, and yel- low crime-scene tape. Te museum provided Several casts of Sue’s vertebrae are CT-scanned at Loyola Medical Center. Larger bone casts had to be scanned at Ford. by the fact that the skeleton is huge even for a large meat-eating dinosaur. Te original bones are incorporated into the mounted skeleton—in the main exhibit hall of the Field Museum—and cannot be removed easily for further work. On the plus side, the skeleton is unusually complete, and relatively few of those bones are not original. Tis was the situation we encountered upon entering the project; our task was to address all these conditions and generate a highly-detailed, complete skel- eton of the T. rex. Learning from the Past Luckily, we had encountered this situation before and knew how to approach the work, accomplish the task, and keep Sue safe and continuously on display; visitors to the Field Museum would be disappointed if she was unavailable for viewing during their trip. We learned many lessons from virtualizing the Smithsonian’s Triceratops and used the solu- tions we came up with for that project—and, in some instances, improvements on them— to facilitate Sue’s entry into the virtual world. Te project was done in three phases. Te first phase was to capture the whole skel- eton in 3D at a relatively low resolution. We did this because the configuration of the mount of Sue was an awesome accomplishment by the Field Museum staff, which evaluated the bones and determined how they should go together in order to put the skeleton in a reasonable posture. Accomplishing this just as well virtu- ally is still far off in the future because it is a very labor-intensive and hands-on process. So the skeleton as mounted represented a great resource that we wanted to use. We decided we must capture the whole thing—11 feet tall and more than 40 feet long. To do this, we enlisted the Chicago Police Studying Sue Access to accurate digital models of fossils has revolutionized the study of bio- mechanics and functional morphology of extinct animals. Techniques such as la- ser and white-light scanning can capture the complex external anatomy of fossils in three dimensions, while CT scanning supplements those by affording internal views of inaccessible parts, such as braincases and marrow cavities. Combined with the powers of CAD software, paleobiologists can now attempt realistic digi- tal models of fossil organisms to estimate size and mass, or determine param- eters such as running speeds or bite forces. A major scanning project to generate an accurate 3D model of Sue’s skeleton was initiated in conjunction with the celebration of the T. rex’s 10th anniversary of being displayed at the Field Museum. Our goals were threefold: attempt to model Sue’s mass from 3D models of her mounted skeleton and scans of indi- vidual bones, use those models to analyze agility, and develop accurate scale versions of bones for research and commercial purposes. In this regard, Sue is a superlative candidate. Her skeleton is not only the largest and most complete T. rex, but the largest skeleton of a biped anywhere. As such, she defines a bio- logical extreme. Given Sue’s size, the scanning project presented some techni- cal challenges that were overcome by combining a variety of techniques. Based on accurate scans of mounted skeletons, body outlines will be mod- eled using irregular ellipses placed at regular intervals (for each vertebra and rib pair, for instance). These ellipses, or NURBS, will be joined to generate water- tight volumes, which can be imbued with densities of various organ systems to generate precise mass estimates for extinct organisms. A particular strength of taking a digital approach to this problem, as opposed to traditional methods of building models or extrapolating from equations governing masses of living animals, is that sensitivity in results to changes within a suite of governing param- eters can be undertaken simply. Despite the completeness of Sue’s skeleton, some bones are distorted and others had loose articulations—meaning some dimensions, such as the width of the rib cage, are more uncertain than others, such as overall length. Likewise, the volume of the lungs and other low-density spaces are hard to fix, but can be mod- eled based on a range of proportional values from living animals, and the effect of such variation can easily be gauged with CAD models. A “flock” of Sue models with different degrees of “fleshiness,” lung volume, and rib-cage dimensions are currently under construction and will yield a best estimate within a broader biologically plausible range of estimates. In addition to overall mass, the center of mass will be estimated, and the models will be given varying quantities of leg muscles, in order to study the effect of body size differ- ences on estimated speed and agility. —Art Andersen July 2010 51 several large monitors so the public and press could view the data acquisition as it happened. Museum staff, the police representatives, and the three of us walked around and answered questions raised by that day’s visitors, and the atmosphere was festive. A total of seven scans were made, covering more than 90 percent of the mount, which allowed us to construct a full virtual copy of it. Tis model already is be- ing used by researchers to study the animal. Te next phase was far more complex and required quite a bit of time. We needed to make much higher resolution 3D virtual models of the individual bones. How we did