G.I. Joe may have finally met his match. (Photo courtesy of Moritz Bächer.)

Tool developed at Harvard turns animated characters into fully articulated action figures

Cambridge, Mass. – July 31, 2012 – Watch out, Barbie: omnivorous beasts are assembling in a 3D printer near you. A group of graphics experts led by computer scientists at Harvard have created an add-on software tool that translates video game characters–or any other three-dimensional animations–into fully articulated action figures, with the help of a 3D printer. The project is described in detail in the Association for Computing Machinery (ACM) Transactions on Graphics and will be presented at the ACM SIGGRAPH conference on August 7. Besides its obvious consumer appeal, the tool constitutes a remarkable piece of code and an unusual conceptual exploration of the virtual and physical worlds.

“In animation you’re not necessarily trying to model the physical world perfectly; the model only has to be good enough to convince your eye,” explains lead author Moritz Bächer, a graduate student in computer science at SEAS. “In a virtual world, you have all this freedom that you don’t have in the physical world. You can make a character so anatomically skewed that it would never be able to stand up in real life, and you can make deformations that aren’t physically possible. You could even have a head that isn’t attached to its body, or legs that occasionally intersect each other instead of colliding.”

Returning a virtual character to the physical world therefore turns the traditional animation process on its head, in a sort of reverse rendering, as the image that’s on the screen must be adapted to accommodate real-world constraints.

Bächer and his coauthors demonstrated their new method using characters from Spore, an evolution-simulation video game. Spore allows players to create a vast range of creatures with numerous limbs, eyes, and body segments in almost any configuration, using a technique called procedural animation to quickly and automatically animate whatever body plan it receives. As with most types of computer animation, the characters themselves are just “skins”–meshes of polygons–that are manipulated like marionettes by an invisible skeleton.

“As an animator, you can move the skeletons and create weight relationships with the surface points,” says Bächer, “but the skeletons inside are non-physical with zero-dimensional joints; they’re not useful to our fabrication process at all. In fact, the skeleton frequently protrudes outside the body entirely.”