Computer Graphics World

JANUARY 2010

Issue link: http://digital.copcomm.com/i/6179

Contents of this Issue

Navigation

Page 10 of 43

Taking ornithologists, it became more and more important to get it scientifically correct," Wang says. Bostwick, who is the curator of the bird collection at the Cornell Univer- sity Museum of Vertebrates (CUMV), provided the CG students with access to museum specimens normally available only to biologists. And, she made it possible to scan a one-of-a-kind specimen of an ivorybill, which had been stored in a jar at the Smithsonian for 60 years, with high-resolution computer tomography (CT) at the University of Texas at Austin's Digital Morphology (DigiMorph) lab. e lab scanned the bird in a natural pose, with the wings tucked, and with the wings slightly open—the specimen, which is the only fully intact one in existence, was too fragile to risk fully opening the wings. From the volume data that resulted, Wang reconstructed the bird using Template Graphics' Amira visualization software for medical imaging. e scans had produced approximately 2000 slices, each with a resolution of 1024x1024. Rather than rendering a volume, Almira's thresholding algo- rithms generated an outline of the skin surface and contours for the skel- eton. e process was far from automatic, however. For example, because the feathers and skin had the same density, the CT scan didn't distinguish between them, so Wang needed to separate feathers from skin. After editing, Wang had an accurate surface representation of the ivory-billed woodpecker's complete skin and skeleton in two poses. Wang then moved the data into Autodesk's Maya and used the reconstruc- tion as a reference model to create a lighter-weight model for animation, with joints in correct locations and a subdivision surface of the skin. He also referred to the stuffed ivory-billed woodpeckers from CUMV for ex- ternal measurements. To best approximate the reconstructed model, Wang "snapped" the majority of the vertices in the base mesh for the skin to points in the reconstructed model, which was dense enough to make this possible. at gave Wang the skin and a rig. Next, he needed to model the bird's feathers. "Because the people scanning the bird were afraid to unfurl the wings, we didn't get great information on the width of the feathers from the CT scan, but we got the length," he says. "However, we were concerned about the pattern the wing cre- ates, not the microgeometry, so I wrote a tool to model the plane of the feathers quickly." Animating the Bird e reconstructed skeleton from the CT scans had provided pre- cise geometrical information about the bones in the woodpecker's wings, but because the model was one solid object, Wang estimated the center point for animation joints. He would fly the bird using traditional keyframe animation; simulating the laws of aerodynamics was beyond the scope of his thesis. However, Wang leaned on ornithologi- cal research for the rotation angles, specifically on work by Ken Dial, who Cornell computer graphics students inspire research in ornithology and aerospace engineering as they study how birds fly Flight January 2010 Science•Engineering n n n n The ivorybill (below, right), with a white trailing edge on its underwing, differs from the pileated woodpecker (below, left), which has a black trailing edge. Photo by Arthur A. Allen. ©Cornell Lab of Ornithology.

Articles in this issue

Archives of this issue

view archives of Computer Graphics World - JANUARY 2010