Meaningful discussion of the broad foundational work performed at the University of Pennsylvania's Center for Human Modeling and Simulation (HMS), under the direction of Norman Badler, is well beyond the scope of this article. Since it is so extensive, and so well known, we will mention only few aspects of the HMS's work, pertaining to their human scaling, modeling, and animation software called Jack (http://www.cis.upenn.edu/ hms/jack.html). As embodied in an agent, Jack is a 3D articulated virtual human currently in use by more than twenty major industrial and military sites around the world [Badler, Phillips, & Webber1993] (see figure 7).
Beyond the just the emobodied agent, HMS is doing general work on supporting user interaction with 3D environments. The use of inverse kinematics (the branch of dynamics that deals exclusively with aspects of motion) in a real-time subsystem allows users to manipulate spatial constraints of the articulated figure as a whole, greatly reducing the burden placed on the system author for creating lifelike movement. Rather than being tweaked for realism ad hoc, the system allows for customization using extant human-factors data. Its (virtual) dynamic interaction with external forces, including self-collision avoidance, is effected through systems that embody simulated sensors. Lastly, gesture and facial expression are controlled from the top down through high-level communicative goals (and c.f. the work of Cassell below).
The authors of the system specify a broad range of applications. Among them are uses of Jack for intelligent agents acting on instructions (through natural language), and for virtual training simulators, appropriate for use in system likes USC-ISI's Steve (see below).
Like IMPROV, Jack does support high-level controls although
in this case it takes the form of a LISP API [Becket1994] rather than
rule specifications. In contrast with IMPROV, Jack uses richer
models and more profound subsystems. The model, being more profound
physically, is a little less flexible to use. A good overview of the various
projects can be found at
(http://www.cis.upenn.edu/ 
hms/badler/pap/pap.html). There is also an
extensive set of pointers to about seventy other virtual humans around the
world at (http://www.cis.upenn.edu/ hms/badler/vhlist.html).