This video is sponsored by Universal Pictures and Mortal Engines.
In New Zealand, Adam Savage sat down with Mortal Engines visual effects supervisor (and fellow ILM alum) Ken McGaugh to talk about the challenges of bringing director Christian Rivers' vision to life. Here's an excerpt; watch the full interview below.
Adam Savage: Describe to me the beginning of a project like Mortal Engines. When are you brought in during the process?
Ken McGaugh: Usually I'm brought in during pre-production. When they start planning on building the sets, how they're going to execute the shots, that's where my involvement would come in. It's making those decisions about what should be in camera versus what should be visual effects. There's lots of constraints around that that are out of our control.
Adam Savage: Right.
Ken McGaugh: That includes the size of the stages that they're building the sets in. I mean, obviously, if we had our way, they'd build complete sets and we'd reserve the visual effects to just what was absolutely required to be visual effects. But that's where visual effects really comes in: It is removing those constraints that filmmakers have, allowing them to go beyond the physical constraints they have when shooting.
Adam Savage: Christian told me they built over 60 sets. Every one of those sets, or many of those sets, have to be integrated deeply into a virtual space that you're also building. So, that coordination must be diabolical.
"It all starts with us serving and scanning and getting texture reference from every set."
Ken McGaugh: It all starts with us serving and scanning and getting texture reference from every set. We'd have a team that would go in after hours and they'd basically just build the virtual version of that set, or they'd acquire all the data necessary for us to build the virtual version of the set. And sometimes we had to build a virtual version of an actual set that we could then render as computer graphics, but more often than not it was to give us the data needed to extend it.
Adam Savage: Right.
Ken McGaugh: The same type of textures, the same design features. We also obviously needed, to a certain level, a version of it for doing our camera tracking. For doing the joins between the virtual set and the real set.
Adam Savage: The biggest thing about the trailers for Mortal Engines are these gigantic rolling cities . As an engineer, I have to say I'm blown away by how much veracity I felt in those machines. As crazy as they are, they really felt grounded in reality. The physics of the movement felt ... it felt sensible to me.
"We had to make things move fast enough to be exciting, and sometimes we did that just by putting the camera closer to the ground so that it felt faster."
Ken McGaugh: I'm so glad that you said that because that was very, very hard for us to achieve. We had to rely upon some of the usual things. Scale ... sense of scale. Some depth hazing, low camera angles, and we couldn't rely upon things moving slow. Things really large tend to move slow and that didn't make it very exciting.
So we had to make things move fast enough to be exciting, and sometimes we did that just by putting the camera closer to the ground so that it felt faster. Other times, we would make things travel fast, so you got ground speed but everything else moves slow.
Adam Savage: Now, when you're talking about this, it's funny because I'm making this transition. When you say putting the camera down low to the ground, you're still talking about in a completely virtual environment?
Ken McGaugh: Yes.
Adam Savage: So, you're moving these machines and running physics simulations, and then I didn't realize you're actually placing cameras to see where it feels the most dramatic?
Ken McGaugh: Yes. A lot of that came out of our post-vis. Which was our previous team working in post visualization, which happens after the shoot. Christian was heavily involved in that, because he actually does a lot of it himself.
Where things would come into animation, where it has a certain energy from the post-vis, but didn't quite work with the physics simulations we have to do. We would slow things down to get the physics working better for things like the dust and the exhaust smoke. But then to get the energy back up into the shot, we would do things like move it closer to the ground so you had trees going past camera.
Every shot, every composition had different requirements for trying to find that balance between scale and excitement, also just a well-composed pretty picture as well, because if you used physically correct depth hazing in aero-perspective, oftentimes London would just be a gray mass.
Adam Savage: Right.
Ken McGaugh: You want some contrasting detail in there, so it gives a fun balance on every shot.
Adam Savage: And this is a film with a tremendous amount of world building. Almost all of your big environments are virtual -- in CG. Right? You're not building football-field sized sets to tell the story.
"While there are few locations around the world that had some aspects that we liked, there was nothing that really fit the bill, so we knew early on we'd be putting efforts into creating a virtual world."
Ken McGaugh: There were some large sets, but you're right, the only environments were virtual. We knew that from the beginning because this is meant to be a world that is unlike our Earth. It was destroyed in the 60-minute war. A lot of the action takes place in the great hunting ground, which over hundreds of years had been crisscrossed with cities of different sizes. So it's a combination of a manmade natural disaster completely shifting the tectonics of the world. Shooting mountains up, causing giant lava filled mountains and then manmade deterioration over and over and over again.
While there are few locations around the world that had some aspects that we liked, there was nothing that really fit the bill, so we knew early on we'd be putting efforts into creating a virtual world that can feel connected to the world we know, but in a way that doesn't feel like it's anywhere you could visit.
Adam Savage: I think that people don't quite realize that when you create a virtual world like that, you're still — just like the real world — placing cameras in different positions and are figuring out where to put lights.
Ken McGaugh: Actually, increasingly so, because the tools that we use get closer and closer to the physics and the closer they get to the real physics, the more we rely upon real world techniques. Both for camera work, for lighting, for animation, and increasingly it's about trying to make things more physically correct.
For instance, the way we light nowadays is very much like you would on the set. We have large area lights. We have silks. We have bounces. We use harmonic range of imagery of real skies. We have physically based sun and atmosphere models. Whereas back in the '90s, you had spotlights, and that was it. The shadows were all fake. So, you had to cheat and every artist had to cheat their own shots and it was really hard maintaining continuity that way.
Adam Savage With an actual engineering standpoint, of course this machine is in real life too big to hold itself together. So, you're making compromises to get it to feel right for the audience. I'm curious if you're running physics simulations where using the actual physics, it just didn't work and you've had to cheat something.
Ken McGaugh: We rely upon physics simulations for things like our exhaust smoke, our dust, our ground interaction, things like that. One of the first passes we had to do was to go in and to get all the speeds. Like I said, they come out of our post-visualization, but those are just recreated just to get a sense of energy and composition for our shot. We unify the speeds because if we didn't, you would actually have exhaust coming out of one of the cities that looks like a train, and the next shot it would be just a thin smear.
To save the effort of every single shot going in and having to fine-tune, because that's some of the hardest things to tune, we'd do a passive go through and unify all the speeds. We found the sweet spot for the chase scene to be around 300 kilometers per hour.
Adam Savage That is insanely fast.
Ken McGaugh: Yes.
Adam Savage: Wow.
Ken McGaugh: So, any slower and it felt slow.
Adam Savage: Really?
Ken McGaugh: Yes.
Adam Savage: So, I really loved when the small ship goes through the track and rides over the hill and the big ship just plows right through the hill. I found myself wondering, were you guys watching footage of bombs blowing up dirt in order to get those things right?
Ken McGaugh: We did. Our main reference for that particular moment was a quarry explosion. So, that's where they submerged in the side of a rock quarry with explosives, and they filmed at high speed the whole rock wall lifting up and exploding. And the first thing you notice, before all the dust comes through, it becomes chaos, is the whole thing looks like liquid. Like liquid expanding. So, we only had a couple of opportunities to try to sell that, but that's the reason why we did this kind of liquid-y effect like you were wringing the carpet.
There's LOTS more cool information on visual effects in general and Mortal Engines in particular ... Watch the full interview below!