A Tangible Interface for High-Level Direction of Multiple Animated Characters Ronald A. Metoyer Lanyue Xu Madhusudhanan Srinivasan School of Electrical Engineering and Computer Science Oregon State University Abstract Many training, education, and visualization environ- ments would benefit from realistic animated characters. Unfortunately, interfaces for character motion specification are often complex and ill-suited to non- experts. We present a tangible interface for basic character manipulation on planar surfaces. In particular, we focus on interface aspects specific to 2D gross character animation such as path and timing specification. Our approach allows for character manipulation and high-level motion specification through a natural metaphor – the figurine. We present an example interface for designing and visualizing strategy in the sport of American football and discuss usability studies of this interface. Key words: tangible interfaces, animation 1 Introduction Advances in computer animation technology, specifi- cally motion capture, have led to natural looking 3D characters that can be controlled at a high level. These algorithms produce strikingly realistic motion while maintaining high-level constraints such as desired paths, poses, or tasks. We are interested in leveraging these algorithms for natural character motion and com- bining them with an intuitive interface for naive users to quickly generate animated content. To do so, naive users must be able to provide high-level character direc- tion in the form of desired paths, tasks, and timing. This paper addresses the problem of specifying charac- ter motion on planar surfaces. This problem is of par- ticular interest in several areas including sports training, military training, architecture, and urban planning. Coaches in American football, for example, often strategize by designing plays on paper. Recent soft- ware packages enable coaches to design plays using a mouse based interface[33]. The ability to create ani- mated content and visualize plays in 2D and 3D would be advantageous because the coaches and players could be presented with several views of the play as it pro- gressed in time rather than being limited to a 2D static top-view drawing. Animated motion could also be used Figure 1. A user specifying passing routes with the coach's table interface. in training simulators for positions such as the quarter- back in American football. Our system allows users to design dynamic content for training and visualization of football plays using a familiar interface – physical icons or figurines (Figure 1). Other applications could also benefit from simple inter- faces for generating animated content. Sports broadcast companies are beginning to use animated visualizations to present strategy to the television audience. The mili- tary generates content of battlefield scenarios for use in training and visualization. Likewise, architects and urban planners could benefit from visualizing pedes- trian motion within a building or in emergency situa- tions. 2 Figurines and Affordances One of the primary factors contributing to the effective- ness of tangible interfaces is the concept of “affor- dances”. When an object clearly indicates the kind of interaction that it is meant to support, that object is said to “afford” its behavior[28]. Figurines, or more gener- ally, physical objects that represent characters, afford the specification of gross character motion, primarily because most people have manipulated figurines to “animate” them for play purposes.