David Edwards Solomon Boulos Jared Johnson Peter Shirley Michael Ashikhmin Michael M. Stark Chris Wyman The halfway vector disk for BRDF modeling. 1-18 2006 25 ACM Trans. Graph. 1 http://doi.acm.org/10.1145/1122501.1122502 db/journals/tog/tog25.html#EdwardsBJSASW06