Computer Graphics World

June 2009 19 Character Modeling•Animation ■ ■ ■ ■ peacock. e crew was able to see a pair in a nearby animal sanctuary, and those birds served as reference material for Kevin's col- ors. Kevin became a 13-foot fl ightless bird with an orange beak, a long, iridescent blue neck, and purple feathers. "John Lasseter always says that before you can caricature reality, you have to understand reality," Jor- dan explains. "To be believable, it has to be inspired by something that could exist." For animation inspira- tion, the studio brought an os- trich to the campus, and the animators took pictures as it walked around outside, but they weren't bound by the real bird's physi- cal limitations. "Kevin is a made-up crea- ture, and probably the character we had the most liberty with," says Clark. "Russell uses her like a pogo stick. Pete always said that if you could hear the sound her brain made, it would be like a dial tone." For Kevin's feathers, the technical direc- tors used one Ri curve for the quills, with hundreds more coming off the sides to produce each barb. "For Finding Nemo, we modeled feathers using wide hair or a single piece of geometry with a clever shader," May points out. "For Kevin, we wanted more geometric complexity. And, because we used individual pieces of ge- ometry, we could model a range of feather types from fl at feathers that we might have done with the shader before, and also fl uff y under-feathers." To color Kevin's feathers, the artists cre- ated a shader that gave the directors the ability to choose which colors turned on and off , and at which angles, as well as tex- ture maps painted with a ramp of all the colors the feathers could exhibit, to control the iridescence. " e order in which colors appear in the map is the order they shift as the angle changes between the camera and the light source," Jordan says. "It's a fairly big cheat, but Pete wanted the ability to turn the iridescence off ." Barking Is So 20th Century For the dogs, the character supervisors and animators spent time in a doggie day-care Kevin is a rare, 13-foot-tall fl ightless bird, colorful and silly. Carl and Russell happen across her after they fl y inside Carl's house to South America. A supposed missing link, she is the ob- ject of (Carl's hero) Charles Muntz's 50-year-long quest. In Kevin's shape and coloration, she, too, reminds us of Ellie: Kevin has a round body, a long neck, and brilliant iridescent feathers. The technical challenges for Kevin were those bril- liant iridescent feathers. In one sequence during the fi lm, a character gets caught in a bolo net. To create that net, rather than using a sheet of cloth with a texture or geometry attached, TD Eric Froem- ling drew on the same rigid-body simulation system used to fl oat the 10,000 balloons carrying Carl's house. "I had fi rst played with this idea on a promo spot for Cars," says Gary Bruins, effects supervisor. "There's a shot where Mater runs into a velvet rope, and I tried connecting spheres to approximate the rope. I talked to Eric about the idea, and he gave it a shot." Here's how it worked. "Eric strung together a series of spheres—rigid bodies—like a string of beads hanging in a doorway," Bruins says. "With enough spheres, we could ap- proximate the behavior of a rope. He made a net by knotting the ropes into a 2D grid. Any time a character interacted with the net, we got a more believable response from the rigid bodies than we would have with cloth. Because it had open squares, if a limb went through an opening, there was no motion on the net." To render the net, TDs ran Ri curves through the centers of the spheres and shaded the curves with rope textures. Similarly, Froemling stitched together a series of triangles and made a quilt of rigid bodies to create a tarp that dropped onto the balloons. As a result, the TDs could more easily make the tarp interact with the rigid-body simulation for the balloons than if they had used cloth simulation for the tarp. Bruins intends to keep exploring this use of rigid bodies to do soft-body simulations. "The nice thing is that you can easily detach the strings of spheres and get ripping and rup- turing, so it has a lot of potential for large-scale cloth and special cases." –Barbara Robertson For animation inspira- tion, the studio brought an os- ject of (Carl's hero) Charles Muntz's 50-year-long quest. In Kevin's shape and coloration, she, too, reminds us of Ellie: Kevin has a round body, a long neck, and brilliant iridescent feathers. The technical challenges for Kevin were those bril- liant iridescent feathers. Net Knots

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