Bringing a project like Christian Rivers’ film Mortal Engines to life was always going to require a significant amount of visual-effects work. Based on Philip Reeve’s novel series, the story takes place in a future dystopia where cities have become massive, roving machines that prowl the surface of the Earth, with London, the biggest of them all, gobbling up smaller cities and dicing them to pieces for resources. There was simply no way to realize the world without heavy use of digital animation. Leading the charge: Weta Digital, the group known for its groundbreaking work on projects like Peter Jackson’s Lord of the Rings films and the Planet of the Apes series.

But while building up the film’s massive, mobile monstrosities was the most obvious challenge, some of the more nuanced work was even more intriguing. I sat down with visual effects supervisor Ken McGaugh (Godzilla, Valerian and the City of a Thousand Planets) and animation supervisor Dennis Yoo (Avatar, The Jungle Book) to talk about using computer simulations to create on-screen destruction, why motion capture isn’t always the best idea, and what Weta hopes to do next.

This interview has been edited and condensed for clarity.

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