Non-photorealistic Rendering of Dynamic Motion
We are using a Java3D environment, modeled after an in-house non-photorealistic rendering system developed at Brown (Markosian, Siggraph 1997). This system is now in use by a substantial number of graduate and undergraduate students at Brown, and the Java3D implementation combines the system's intuitive camera manipulation with the the latest Java3D benefits.
The physical parameters to be displayed in this project come directly from physically based simulations or from other sources such as motion capture data. When other motion sources are used, we will calculate the required information using techniques such as inverse dynamics, a method used in robotics to calculate the control torques needed to generate a desired motion.
This project is in conjunction with ongoing research at Georgia Tech.
Currently, the Gatech group is exploring new techniques for emphasizing
the overall dynamics of human motion. See below
for more information.
Currently, we have designed three devices to represent
different aspects of a runner's motion, and have more in progress.
These devices include a center-of-mass shadow, ground contact force arrows,
and joint trajectory tracers. Each can be used on either one or multiple
runners, for teaching or comparison purposes.
|A center of mass (COM) shadow is the projection onto the ground plane of a runner's center of mass. The circular shadow has radius proportional to the COM's height (z direction). As the runner's body shifts weight in the x-y plane, the shadow moves across the ground. When the COM's z coordinate decreases (i.e., the COM moves closer to the ground), the shadow's radius increases linearly. Similarly, when the COM moves away from the ground, the shadow's radius shrinks. Using motion tracks from the simulator developed by Hodgins and Pollard, we found that both an adult male model and a child model project their COMs on the area between their feet.|
|Ground Contact Force Arrows display the
magnitude and direction of the forces applied to runners' bodies as they
hit the ground. The simulator generates force data for support-phase
frames in the form of a reference point and force vector. The Force
Arrows disappear for non support-phase frames, since no ground contact
forces are applied then. We have found that at the end of the flight
phase, the foot strikes the ground with a significant forward force.
A Force Arrow shows the equal-but-opposite force applied by the ground
on the foot. Then, as the foot stabilizes and prepares for lift-off,
the ForceArrow changes in length and rotation, intuitively showing the
effects of the runner's shifting weight.
|Tracers plot the movement of a joint over time. Every given number of frames, a Tracer appears in the Java3D universe, marking the location of the joint at that frame. Tracers emphasize the periodicity of a motion, as well as highlight any differences between cycles. Tracers also enhance motion comparisons, displaying, for example, that at a particular frame, Runner A's elbow is much higher than Runner B's elbow.|
2D plotting of joint position over time - overlaying graphs from two runners for comparison
2D plotting of foot/arm height over time - overlaying graphs from two runners for comparison
2D bar chart comparing torques on all body parts for a given frame
Horizontal lines to emphasize stride length
One style that has attempted to render figures showing movement is Italian Futurism (1909). Although tangled up in the politics and violence of the time, the artists of the Futurism movement tried to provide a portrayal of energy and speed through their paintings, photographs, and sculpture. Many of their stylistic techniques lasted beyond the period.
Often their figures appear to be off-balance and leaning or falling in a particular direction (Boccioni, Riot in the Galleria, 1910 and Raid 1911). In Raid, an additional technique, "lines of force" is evident. Rays of light form multiple lines to heighten the appearance of distress in the crowd Tisdall,1978). Another artist in the movement, Balla, used multiple images of a sparsely rendered subject to convey a feeling of motion (Balla, Leash in Motion, 1912 and Girl Running on a Balcony, 1912). And finally, Boccioni experimented with gross distortions of the shape of the muscles to illustrate the motion of a sculpted figure (Boccioni, Spiral Expansion of Speeding Muscles, 1913).
In this project, we will render motion data as animations, images, or textured statues. All the non-photorealistic rendering techniques that we develop will attempt to emphasize the motion in the scene.
Very Abstract Rendering