We describe an interactive graphics system for the entry of three-dimensional moving points from multiple perspective views. This work represents a major extension of Galatea, our system for graphics-assisted 2D motion analysis. 3D Galatea permits reconstruction of 3D time-dependent positions from 2D entries in two or more perspective views.

A technique often employed in animated vector graphics involves the use of a real-time playback mechanism. This technique is an alternative when it is not possible to generate animation frames in real-time. Instead frames are compiled in advance at non-real-time rates, saved in secondary storage, and then played back at desired real-time rates. The basic design of such a playback mechanism will be considered, including discussions of synchronization, buffering, and blocking. Two special properties will be established for these systems: the conditions required to achieve real-time reversal in the direction of the playback sequence, and the existence of upstream/downstream effects, performance differences between directions in systems that are run "too fast."

GALATEA is an interactive animated graphics system providing a tool for the man-machine analysis of moving images recorded on film. The system relies on the user's recognition of phenomena of interest and his manipulation of simple graphical objects to build up a kinegram, an animated representationof the film. Display of the kinegram superimposed on the original film facilitates the entry and refinement of the animation. The net result is an analysis by synthesis. In this paper we describe the current production version of GALATEA from the standpoint of the user. Included are a functional description of the constituent hardware, demonstration of various aspects of system behavior, and some examples of interactions common in user applications.

The extraction of information from movie film and videotape has always been a very tedious process. Yet the usefulness of these media in biomedical research, behavioral science, industrial testing, etc., is apparent. We are developing a system, GALATEA, for the rapid extraction of data from film or video using interactive graphics. The key aspects of GALATEA are: The user indicates what features are of interest using an x, y digitizing pen. These pen positions are the only data the system sees, so that full digital image encoding is avoided. The user can trace the features while the fim runs (frame-by-frame analysis is not necessary). The user has constant feedback in the form of an animated, computer-generatedmovie (Kinegram), overlaid on the original film image and running synchronously with it. It is this kinetic feedback of the data entered that makes the system efficient. Structured programming, real-time programming techniques, data structures for time-dependent pictures and dynamical graphics tools are covered. A detailed discussion is given of Slippage or soft degradation in real-time systems under fluctuating load conditions.