Meanwhile, the Transport is the armored vehicle that lets off aliens during the New York invasion. It's like a worm that flies. "The animation challenge was figuring out how it flies," White explains. "We didn't want it to look like a porpoise and so finding the right speed was tough. If it went too fast, it looked small, but if it moved too slowly, it looked boring. We added electricity crackling down its side and it has heat wash coming from under its wings to stir up the ground."

This was Weta's first crack at Iron Man and they redid the ILM textures using the proprietary Udim. Image courtesy of Weta Digital.

As for Iron Man tweaks, ILM introduced the Mark VII suit. "We're back to a round RT on his chest but the biggest change was giving him a rocket pack. That was a conscious decision by Joss to give Iron Man different poses and not have his hand always as part of the thrust component. We also provided a little extra weaponry with a hand laser and thigh missiles."

Weta Digital got to play with Iron Man, too, especially for the mountain top fight with Thor. "We shared assets back and forth with ILM, but our pipelines are unique and it's hard for other assets to plug into it," explains Weta's VFX supervisor, Guy Williams. "But in this case, we got their models and we had to redo the texture spaces because the way we texture maps is different. We use a system called Udim and instead of putting all of our texture spaces from zero to one we lay them out in this very large grid so there are individual zero to one spaces. It allows us to have thousands of maps on a model and not have to do any arbitrary system for defining which spaces go to which maps.

The mountain top battle between Iron Man and Thor was the biggest sequence, utilizing fractured and prefractured destruction. Image courtesy of Weta Digital.

Iron Mans simulations were done in Maya, Houdini and the in-house Synapse. Image courtesy of Weta Digital

"To migrate ILM's texture spaces to ours, we use ray tracing. We look at their turntables and just try to mimic it. In this case, we also had the beautiful suit from Legacy and we were both trying to up our game. We really got into the multi-layered car paint with the clear cut polish on top for Iron Man's finish."

Weta not only created a lot of destruction during the mountain top fight but also during the preceding Museum Square sequence (filmed in Cleveland but refashioned to look like Stuttgart) and then during the later Helicarrier attack. Weta uses Maya's particle solver for dirt, dust particulates and sparks. When large quantities of debris were simulated, they were also in Maya's regular particle solver and instanced as geometry at render time.

Big explosions were simulated with Maya fluids. Image courtesy of Weta Digital

The secondary motion for trees and plants was simulated with a plug-in curve solver in Maya (on the render wall). The curve animation was applied to the trees at render time in RenderMan with another in-house plug-in. Most hero close-up destruction required enough art direction that they combined both fractured and prefecture techniques. Mid and distant destruction was mostly procedural or even rigid body grenades (emitting rigid bodies from a particle emitter, part of Weta's in-house rigid body toolset).