Affiliation: | (1) Department of Computer Science, University of Illinois, Urbana-Champaign, 1304 W. Springfield Ave., Urbana, IL 61801, USA E-mail: jch@cs.uiuc.edu, ES;(2) Ogden Profession Services, U.S. Environmental Protection Agency, Corvallis, OR 97333, USA E-mail: brent@heart.cor.epa.gov, US;(3) Alias | Wavefront, 210 King St., Toronto, ON, M5A 1J7, Canada E-mail: jmichael@aw.sgi.com, CA |