Weta Digital’s models supe on The Hobbit

fxguide recently visited Weta Digital in Wellington, New Zealand to cover their incredible visual effects for Peter Jackson’s The Hobbit: An Unexpected Journey. One of the talented artists at Weta Digital is models supervisor Marco Revelant, who took us through the challenges of creating so many digi-doubles on the show, and some new tools for trees, feathers and fur.

Digi-doubles

An Unexpected Journey makes extensive use of digital doubles – replicas of Gandalf, Bilbo and the Dwarves, for example, were each generated as photoreal CG actors both for scenes in which they are performing elaborate stunts but also for many scenic traveling shots. Many other digi-doubles in crowd scenes and epic shots are also featured.

To create the digi-doubles, Weta Digital began with scans and photographic reference of the actors. In particular, turntable shoots of the characters in costume, plus close-up photography of pieces of clothing, armor and make-up, were undertaken. A CG turntable of the final character could then be easily compared to the original reference.

Watch a breakdown of the Goblin cavern sequence, featuring CG modeled environments, Goblins and digi-doubles. Note: there is no sound in this video.

Weta Digital used its Gen Man asset as a starting point for digi-double work with all the necessary rigged bones and muscles, and then adapted it for each character. Modeling and animation is done with Mudbox and Maya. The studio’s linear-elastic finite-element system, Tissue, was relied on to build muscles, skin, and fat and add realistic simulations and deformations. Barbershop, Weta Digital’s hair toolset, was used to create a wide variety of hairstyles (see more below).

An additional evolution in the digi-double approach from Weta Digital was in the area of cloth simulation. For An Unexpected Journey, artists looked to Korean fashion software Marvelous Designer. Using the original costume patterns, these would be re-modeled and then ‘draped’ on the character in the software to provide an accurate representation of how real clothing would look.

“We ended up with clothing that was correct from a fold and material point of view,” explains Revelant. “It also scaled. We could simulate it on different levels and increase resolution when it was needed.”

Revelant also notes that in traditional clothing sim work one of the problems as a modeler is sculpting realistic folds. “The problem is that with material you have to do folds but that means taking it away from somewhere else,” he says. “But with Marvelous Designer this was possible – you could take a piece of clothing and move it around.”

For crowd scenes – both for humanoid and more creature-like characters, such as the Goblins – Weta Digital deferred to both Massive but also a revamped creature pipeline, especially since many would shown up close. Massive’s brain and a comprehensive library of motion capture elements were used in conjunction with improved crowd facial animation tools.

Growing trees

Although it had generated CG trees on enormous occasions prior to The Hobbit, Weta Digital stepped up its foliage and tree models for An Unexpected Journey with a new tool called Lumberjack. “What we wanted from Lumberjack was a tool that was able to create the procedurally trees that looked very realistic and set up in a way that were easy to simulate for wind and destruction,” says Revelant.

“We also had to extend trees that were already built on set, for example, Greenwood Forest where Radagast lives. There was this big set with big oaks built up to a level – up to six meters and then it stopped. A completely procedural system would have been a problem because you can’t make something that is that specific.”

The trees created in Lumberjack feature strongly in the film, combining with practical set-dressed trees as well.

To cater for realistic tree simulations – both for subtle shots of them blowing in the wind and then more complicated destruction shots – and to enable art-directable trees, Lumberjack was crafted to operate in two ways. First, an artist could draw curves and generate geometry out of curves. Or, in the case of say Greenwood Forest, a LIDAR scan of the set could be used as a starting point and extended to create a canopy of a given size with procedurally generated secondary branches and leaves.

Lumberjack is based on biological modeling and visualization research by Dr. P. Prusinkiewicz and his colleagues at the University of Calgary in the field of natural growth systems. It sets out rules for light, space for growing and shading. “You use all these sources to simulate the growth of a tree,” says Revelant. “It’s not an L-system or traditional procedural system, but is based on biological parameters.”

The system is built inside Maya. “We created a Lumberjack node that included pretty much all the tree,” explains Revelant. “You have an OpenGL instance in Maya, you have a single node and this node contains all the tree, including curves that can be pulled out for animation and then can be pulled back in. Editing the curves allow you to art direct the tree. Even if the tree is completed, having all these curves allows you to move the branches around and keep the hierarchy. So if you want to move a big branch around, say the main branch out of the way for a shot, you can do it and all the secondary branches will follow properly.”

From feathers to fur to stone

As recently as The Adventures of Tintin: The Secret of the Unicorn, Weta Digital had worked on a feather system for a falcon. That system, called Plumage, was developed further on An Unexpected Journey for the Great Eagles. “The step forward was to try and introduce a nice collision between feathers and the sliding effect you have between one feather and another,” says Revelant. “We also needed to define the look with fast turnarounds.”

Catch a glimpse of some of the creatures and effects created by Weta Digital for An Unexpected Journey in this TV spot.

Artists broke the different feathers down into different ways of controlling them. There are hero feathers that animators need to control, which they control via the puppet. Then other feathers in the neck are more reactive to forces like wind or collisions – these ones are procedurally created. The interrelation between hero and procedural is solved at a different level.

“Going from rest position to flight was difficult because you have a lot of collision going on,” notes Revelant. “How a bird works is quite a complex thing. A lot of the joints on the wings are not like a nutcracker joints, but work on off-set pivots. So when they fold they fold underneath.”

Other animals, and digi-doubles, came to life also via fur and hair simulations. Weta’s proprietary fur system, Barbershop, was used here to craft Warg and rabbit fur, hedgehog spikes and various character hairstyles. “Barbershop is a little bit different from normal fur systems,” says Revelant. “It’s more of a sculptural tool rather than a procedural tool.”

Stone-giant model.
Final Stone-giant shot.

“We changed our approach for braids, for example,” adds Revelant. “Before, we would tend to do these with geometry, but this time we went with full fur. We had a simple procedural tool that creates the braid for you, you define the spacing and tension, and then we created some simple geo like NURBS geometry so you can judge it. Then it does the fill with hair, starting from the growing surface. After that you have the full functionality of Barbershop to edit this braid. You can pull out hair, cut them, you can create fly-aways. You can un-braid the braid, because during a fight it can lose the shape.”

An almost completely opposite challenge to feathers and fur came in the design of the Stone-giants, who fight each other but must stay in a relatively rigid form. Despite that, much of the drama of the scene came from pieces of rock simulated to fall away from the giants, and a lightning storm developing behind them.

Weta Digital also looked to LIDAR data from mountain scans in New Zealand to help with the Stone-giant topology. For much of the dense meshes as a result, artists looked to CySlice from Headus to extract displacement maps. “We started using Ptex,” notes Revelant, “but it’s still mainly UV based. We use CySlice because the point of extraction is really good and it has solved a lot of problems without spiking or creating a lot of artifacts in the extraction. There’s also a huge amount of polys – we are able to extract from 50 million faces of hi res to low res. We also worked with Headus to develop shrink wrap technology and create geometry for rocks.

Start with reality

Weta Digital’s strength has always been to approach its CG modeling and creature work by starting with something real – from skeletons, skins, movement, cloth and of course through to lighting and environments. “When you do something from reality you have a certain kind of behavior that is easy to see and plan ahead for, says Revelant. “The by-product is that what you give to a creature is physically valid – it’s not something that they have to fix to make work.”

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