Issue: Volume: 24 Issue: 2 (Feb 2001)

Grecian Gears




An animator cranks up an ancient machine

By Jenny Donelan

One hundred years ago, Greek sponge divers discovered an ancient shipwreck off the coast of Antikythera, an island in the Mediterranean Sea. The contents of the first-century BC vessel-fine bronze and marble statues, gold jewelry, and other works of art-were so impressive that some unwieldy hunks of wood and metal found among them were initially overlooked. As museum technicians began cleaning the fragments, however, gears, dials, and a set of complex instructions revealed themselves from beneath a wooden framework that fell apart as it dried in the air.

From reading the inscriptions, researchers determined that the so-called Antikythera mechanism was a complex astronomical calendar-actually a primitive computer for calculating the positions of celestial bodies-that may have been used for navigation. But not until recent years has the true complexity of the device become clear. With its 20 or more toothed gears, including what appears to be a differential gear assembly, the 2000-year-old mechanism represents technology that had not been thought to exist until the thirteenth or fourteenth century. "It's like opening a pyramid and finding a jet engine inside," says one researcher.

The ramifications of such a device, and how it is reshaping our understanding of ancient Greek technology, inspired modern-day Athenian Adonis Kotzias to create a film about it. "Scientists from around the world are discovering that ancient Greek culture was not just based on philosophy and art-it was very technologically advanced," says Kotzias.

Last year, while working at The Foundation of the Hellenic World, a nonprofit cultural institute in Athens, Kotzias began discussing an animation of the device with architect Ioannis Arvanitis. Based on these discussions, Kotzias was able to create a proposal for a postgraduate project with the Glasgow School of Art in Scotland, where he had received a master's degree in 2D/3D motion graphics and virtual prototyping.
An ancient ship bearing a mysterious cargo heads into a storm in a Softimage animation created to dramatize the discovery of an ancient Greek technology.




The plan for the three-and-a-half minute film was simple in terms of plot. "The Antikythera Mechanism" depicts a merchant vessel as it would have appeared about 80 BC, when it is supposed to have sunk. The ship sails through calm, then stormy, seas, eventually sinking. A new day then dawns on wreckage floating in the water. At the end of the film, the Antikythera mechanism appears in the heavens, whirling past the sun, moon, and stars, in what is, in Kotzias's words, "a symbolic expression of what this mechanism can do."

Less straightforward than the story line were the tasks of animating the movements of the ship, the water, the wind, and the device itself. First Kotzias modeled the vessel, a Roman merchant type about 50 meters long. He modeled the craft in Softimage|3D, using a number of inverse kinematics skeletons that would be employed later to make the ship react with the sea. For hardware, Kotzias used a 650mhz dual-processor NT PC and an SGI O2.

Two small human figures, also modeled in Softimage, appear briefly on deck and atop the mast, but the main drama belongs to the interaction between the ship, the wind, and the waves. These elements were linked procedurally. As the water, which Kotzias created with tools from Arete, becomes rougher, the ship pitches and rolls accordingly. Other elements of the vessel-the sails and the rigging, for example-were similarly linked to the action of the wind using Softimage dynamics. Coordinating these relationships proved one of the greatest challenges of the project. However, Kotzias eventually got all the elements working together by writing his own procedural equations.
To add details to the ship model--the prow that resembles a goose, the square-shaped sails--the creator of "The Antikythera Mechanism" film turned to ancient representations of similar vessels from the time period, about 80 BC.




The next challenge was to animate the Antikythera mechanism itself. Thanks to extensive study-notably by Derek de Solla Price, whose 1959 Scientific American article first pointed out the mechanism's true complexity, and later through analyses with X-rays and 3D graphics-researchers have a fairly good idea of how the device worked.

Scientists believe that it was set in motion through a handle or crank. Kotzias, who cites a lack of mechanical experience, found it difficult to digitally represent the application of such a relatively unsteady force to an input gear that in turn sets in motion all the different-size sets of wooden gears with triangular teeth. He credits his former colleague Arvanitis with writing the procedural equations that eventually powered the virtual device.

Arvanitis used published information about the Antikythera mechanism to derive mathematical expressions for the 31 gear splines needed for the model. "When we started to construct the model, neither Adonis nor I was sure of what some of the gears represented," says Arvanitis. "But after all the expressions were entered, the function of every gear became obvious." Eventually, says Kotzias, "We could just rotate the input gear and the whole mechanism would work exactly the way it did 2000 years ago."
The gears turn for an animated Antikythera mechanism. Its physical counterpart is too fragile and incomplete to be operated.




Once the animation was completed, Kotzias added textures created by artist Lydia Abastado. He employed Mental Ray shaders from Mental Images to integrate nighttime clouds and stars into the scenes.

"The Antikythera Mechanism" will be shown at Siggraph this summer as part of an exhibition of student work from the Glasgow School of Art. Kotzias, who is now employed as a 3D animator with the Glasgow-based Digital Animations studio, hopes the film will inspire viewers to learn more about the inventions of ancient Greece. "We Greeks are doing fine now," he says, "but compared to the past we are nothing really." He says that this fascination with a civilization that at its apex bested not only modern Greece, but the rest of the world as well in its achievements, was his inspiration for the piece.

Key Tool
Softimage|3D, Softimage (www.softimage.com)

Images courtesy Adonis Kotzias.
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