Ju-Whan Song Ou-Bong Gwun Seung-Wan Kim Yong-Guk Kim A Boundary Surface Based Ray Casting Using 6-Depth Buffers. 1134-1140 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3314&spage=1134 2004 conf/cis/2004 CIS db/conf/cis/cis2004.html#SongGKK04