First, a system for simple and natural direct manipulation of 3D objects was created. This system, which we call Object Associations, is a software framework that provides a unified method for designing and implementing convenient direct manipulation behaviors for objects in a 3D virtual environment. A combination of nearly realistic pseudophysical behavior and idealized goal-oriented properties is used to disambiguate 2D mouse actions on the display screen into appropriate and natural object motion in the 3D virtual world, and to determine valid and desirable final locations for objects being manipulated. Objects selected for relocation actively look for nearby objects or structures to associate and align themselves with. An automated implicit grouping mechanism falls out of this process. Concept, structure, and our implementation of this framework are presented.

Second, the realism of the WALKTHRU real-time rendering system was enhanced by the addition of physical simulation software. A first set of routines provides the virtual user with an adjustable eye height, which is dynamically maintained through a combination of feedback control techniques and discrete time physical simulation. This gives a much more natural feeling to moving through the building, allowing the user to look up and down while walking, and permitting realistic use of stairs and elevators. In a separate experiment, the Lin-Canny closest features algorithm and a fast contact force computation algorithm was integrated with the object associations system, allowing true collision detection and pseudo-static simulation of moving objects. The implementation, tradeoffs, and success of this experiment are presented and discussed.