Simulating the Balloon Canopy in “Up”

"The sheer number of dynamic bodies in the balloon canopy in “Up” required a reimagining of Pixar’s rigid-body simulation environment and development of concise rigs and exible artists’ tools"
Jon Reisch, Eric Froemling
Pixar Animation Studios
http://news.cnet.com/8301-13772_3-10249396-52.html

Challenges
lots of balloons – tens of thousands
lots of shots – close to 200
lots of action – popping, churning, withering , a character in itself.

Early testing – procedural motion
What makes balloons feel like balloons? – the bouncing. He tried particles – driving balloons using fluid - didn't work. He tried rigid body tests – they liked this
Existing toolset limitations – designed originally with Ratatouille. It became clear not good enough for all of these rigid bodies
step 1 - strip this whole thing out of maya – throwing in 125,000 bodies
Ballooning with 'Ned' – the system - I think it is proprietary
balloons on bottom of hot air balloon are smaller because camera is most often at the bottom
hot air balloon – so the larger balloons at the top of the canopy are still visible and not like funny pixels.
Simulating the strings – didn't do all of them
Building a canopy with shapers and noise to keep it slightly alive.
Canopy Spine Rig – needed more structure
Wilting – did have to cheat – the balloons wanting to come into frame
Hero Balloon Rig - actually simulated the string