A HYBRID RAY TRACER FOR RENDERING POLYGON AND VOLUME DATA

Volume rendering is a technique for visualizing sampled functions of three spatial dimensions by computing 2D projections of a colored semitransparent volume. In this article I address the problem of extending volume rendering to handle polygonally defined objects. The solution I propose is a hybrid ray-tracing algorithm. Rays are simultaneously cast through a set of polygons and a volume data array. Samples of each are drawn at equally spaced intervals along the rays, and the resulting colors and opacities are composited together in depth-sorted order. To avoid aliasing of polygonal edges at modest computational expense, I use a form of selective supersampling. To avoid errors in visibility at polygon-volume intersections, I give special treatment to volume samples lying immediately in front of and behind polygons. I will evaluate the cost, image quality, and versatility of the algorithm using data from 3D medical imaging applications. © 1990 IEEE