Knowing your underground effects

11 May, 2009 by IF

By Rodney Appleyard

Animal Logic’s VFX supervisor, Andrew Jackson, recently told us how he worked closely with director, Alex Proyas, to create a dramatically convincing underground train crash sequence for Knowing.

What was your brief for this sequence?


Knowing director Alex Proyas described the overall VFX approach to this film as ‘documentary style’, with realistic camera movements that allow the disaster sequences to feel like they actually happened and someone had been there to capture them. 

How did you work with the director to plan the VFX for the subway scene?

The sequence had been roughly storyboarded – this was used as a starting point by previs artist Alfie Olivier, to set up the whole scenario as a single animation. The scene was then rendered through multiple cameras and cut together by editor Ritchard Learoyd. At this point we would get feedback from Alex to fine-tune and adjust each of the shots.

Which live action shots were taken for this scene?

There were several approaches used in this sequence. The tunnel shots were almost one hundred percent 3D – only the carriage fronts in some of the shots were live action. For the main platform shots, we made the decision to put as many elements as possible in the live action plates – these included 200 extras, practical dust, smoke, debris, sparks and stunt people on wires.

We also included two green screen shoots. One with exploding columns and one with more flying stunt people on wires. For the interior shot of the rolling carriage, we filled a green box with stunt people and tipped it on its side! We then added extra layers of stunt people and replaced the green box with a 3D train interior.

Were you on set and involved with the shooting of the live action shots?

The train crash sequence was shot at the same time as main unit were shooting another sequence, so Kimble Rendall, (second unit director) and I were solely responsible for shooting the subway live action plates. The whole crash sequence was shot over just three days, plus over the two green screen elements shoot days. 

How many real trains were used to shoot the sequence?

All the stationary trains at the platform were real. The station set was built inside a rail yard in Melbourne, so we had access to actual trains, although we were not able to move them during a shot.

How did you merge the VFX with the live action?

For several reasons I decided not to use any green screens on the station set. Firstly, if we had done that, we would have covered up the actual set that we wanted to see; secondly it allowed us to include extras, stunts and SFX in one take. Breaking shots like these up into multiple layers would have taken much longer and we would have lost a lot of the interactive lighting from the practical effects. The only CG elements were the train carriages and some extra dust and debris FX layers.

Can you describe in detail the post production process?

The first step after the shoot involved making selects and editing them into a sequence. Once this had happened, a 3D camera track was generated. We used several tracking software packages for this task (Boujou, PF track and 3D Equaliser).

Before postvis could lay out the 3D trains into the actual shots, we needed to generate a rough roto of the foreground objects – this allowed us to see the action more clearly. The postvised shots were then refined in the edit and when everyone was happy, they were moved to final production.

This final stage involved replacing the 3D temp train with final assets – we built five levels of damaged trains, which we could switch at the point of impact. All the 3D elements were built and animated in Maya and rendered in RenderMan using Animal Logic’s MayaMan.

The rendered trains were composited into the live action plates in Nuke, along with the exploding columns and extra stunt people.

What reference material did you use? How did this help?

As with all effects, animation reference is absolutely vital – we studied at great length all the train crash clips we could find.

How significant do you think the colour grading was in making this scene realistic?

The actual colour grade was mostly an artistic choice. I do however think that the overall dark, dusty and gritty atmosphere helps to draw the viewer into the scene as if they were actually there.

How did you build and create the surfaces, textures and colours?

We took literally hundreds of photos at the location. These become the basis of most of the 3D texturing for both the train and the environment that was built in 3D.

Were any proprietary programs built specifically for this scene?

Not specifically for the Subway sequence, however there were fire simulation tools developed for some of the other disaster sequences.

I think it’s really dramatic when you see the train crashing through the pillars and knocking people out of the way – how difficult was it to make this look realistic and how did you pull this off so well?

I think the key to the success of this sequence is the fact that the original plates are so full of action. Even if we ended up covering up some of the elements with extra layers, we had a solid base to work from and perfect reference for how it should look.

Also, having prevised the sequence accurately and sticking to those shots is a huge help in complex scenes like these. I feel the practical on-set SFX by Angelo Sahin had a huge impact on the final look of the sequence.

Anything else you’d like to add?

Big effects sequences like this are only possible with the collaboration of a huge team of talented and committed people, thanks to all of them.