Navigation and Manipulation

New techniques that make virtual characters perform mundane tasks more realistically
Natural movement of game characters is very important in games and simulations. However, specific tasks such as opening doors or picking up a gun are often poorly animated in games. We have developed techniques that make the character perform these tasks more realistically. Characters in games generally can do many different actions such as walking, running, or jumping. A common technique to obtain realistic animations is by using motion capture. By tracking the motions of an actor it is possible to have a game character perform the exact same movement as the actor. However, the more actions a character should be able to perform, the more motion capture recordings are needed, leading to huge motion databases. Furthermore, a lot of manual work is required to ensure that transitions between motions look natural. We focus on finding automatic techniques for generating realistic character motion.

In our technique, motions are generated separately for the upper body (picking up an object) and lower body (walking). The upper body arm motion is created using techniques from robotics. The lower body motion is created by combining and reusing recorded walking motions. After the animations for both the upper and lower body are created, they are stitched back together. The input for our animation system is a sequence of foot placements, which can be drawn by an animator or calculated automatically from a path that the character should follow. We store a database of walking motions which are automatically separated in different footsteps. New motions are then created by smartly interpolating between these footsteps in the database, combined with a fast parameterization scheme that describes the footsteps using only a few parameters. We then combine the different footsteps to get the final animation. Our technique is fully automatic and needs no editing or post-processing. Furthermore, our technique is real-time. Because we separate the lower body from the upper body, we can now combine upper body motions with the generated motion to perform tasks while walking such as picking up objects or opening a door.

Many game companies can benefit from this new technique. First of all, the technique can generate animations that walk and pick up objects simultaneously, which is not possible with current techniques. Second, our technique requires less recorded motions. Game companies can therefore spend more time and money on other aspects of the game. We are currently looking into applying a similar technique to the upper body to generate realistic upper body motions based on a small corpus of recorded data. This way, an animator can generate motions based on how a character interacts with the environment fully automatically without having to worry about how the motion is constructed. Furthermore, we are investigating how physical properties can be incorporated in the system, so that the animation is adapted automatically to the constraints of the environment.

Workpackage
3.1 Navigation and Manipulation

Partners
Utrecht University

Key Publications
B. J. H. van Basten et al. (2010). Combining Path Planners and Motion Graphs. Computer Animation and Virtual Worlds, to appear.
A. Egges et al. (2010). One Step at a Time: Animating Virtual Characters based on Foot Placement. The Visual Computer, 2010. Special issue of selected papers from Computer Graphics International.
B. J. H. van Basten et al. (2009). Evaluating Distance Metrics for Animation Blending. Fourth International Conference on the Foundation of Digital Games (FDG 2009). More publications.

Contact details
Arjan Egges, Utrecht University
J.Egges(at)uu.nl