Late in post Zoic Studios was called in to create 30 shots for the gritty sci-fi feature District9 including creating a complex shot showing the strange alien blood, which emulates ferro fluid. We spoke with Zoic’s Creative Director/2D Supervisor Patti Gannon and CG supervisor Trevor Adams about this and other VFX shots they handled for the film.

What did your work entail on the film?
PATTI GANNON: Weta, Image Engine and The Embassy were the primary vendors. We were called in late to the game to do about 30 shots. One of the more complicated shots was doing this alien fluid. It’s based on the physics and principles of ferro fluid which reacts to electrical stimuli. They drop this fluid into another bit of fluid and it reacts in a geometric manner when an electric current is passed through it. The gets cleansed and then it goes down into a fuel cell. It was unusual work to do. It is based in science but it was a completely different take on what you think fluid is supposed to do.

TREVOR ADAMS: We got great reference from [director] Neill [Blomkamp] in regards to what he wanted. We tried a bunch of different methods using different software packages but we ended up using Maya with a couple deformer scripts we wrote and that seemed to work out well. The idea behind it is that is an actual fluid that reacts to electrical current. When you apply electricity to it creates these geometric shapes within itself.

We tried Realflow and Houdini and all sorts of more dynamically based toolsets but we found that actually getting in there and animating it manually created a better effect. We needed a certain amount of control and trying to do it dynamically got too tricky. We played around with sine wave deformers and then hand-animated the effects. RealFlow and other things like that base their physics on real fluid. This is scientifically based but not your normal fluid. It’s has a dense feel to it, like that of mercury. We did some secondary animation with a lattice deformer and moved that around to give it a thick feel to it. Then on top of that we added the sine wave deformer that creates the patterning on the surface.

What other shots did you handle and what were the challenges of those?
GANNON: We created a CG armored vehicle that gets blown up and slides toward camera. We did a rocket propelled grenade and lots of bullet hits. We also created the MNU headquarters adding the building’s signage, helicopter pad and helicopter.

Talk about the CG vehicle getting blown up.
ADAMS: The practical explosion kicks up all this dust and debris and we have to make a CG vehicle that fits in the middle of that scene. We had to recreate a lot of that on the CG side and then put that on top so it fit in the scene and didn’t look so crisp. The tricky part about it was trying to integrate it into the plate because there was so much dust and a strange look for a film. It’s this desaturated, nasty looking environment so we had to match that aesthetic.

GANNON: It was shot gorilla style, handheld plates. The area they shot in South Africa is a polluted environment so putting CG in any of these shots was a difficult task in terms of the tracking and lighting in order to get the CG elements to fit in there. It wasn’t making something look pretty and placing it in a scene. It was all very raw and gritty.

ADAMS: All of this was handheld so there was nothing to lock on to. We had to d a lot of massaging with boujou to give us a track that we could use. We modeled the vehicle in Maya, rendered in mental ray and used Maya Fluids and practical elements for all the dust.