http://www.usc.edu/dept/raiders/ To appear in the IEEE International Conference on Robotics and Automation, May 19-26, 1995, Nagoya, JAPAN. This work was supported in part by NSF Young Investigator Award IRI9457523 to Prof. Goldberg, who can be reached at [email protected] or (+213) 740-9080. A very early version of this paper was presented at the Second International WWW Conference, Chicago, IL...