Steven Martin Han-Wei Shen Ravi Samtaney Efficient Rendering of Extrudable Curvilinear Volumes. 1-8 2008 PacificVis http://dx.doi.org/10.1109/PACIFICVIS.2008.4475452 conf/apvis/2008 db/conf/apvis/pacificvis2008.html#MartinSS08