Volume rendering is a technique for visualizing 3D arrays of sampled data. Volume rendering, though capable of performing very effective visualization, is very computationally intensive. Semi-boundary (SB) is a compact data structure used to encode extracted surface from volume data. In this paper, we describe an incremental algorithm to shorten rendering of SB nodes. We define two projection rules to guarantee proper projection order and, thus, eliminate the requirement for a Z-buffer. Using these two rules, we save data storage as well as rendering time. As a result, the proposed method can achieve interactive rendering performance for a large volume pelvis data set with a size of 512 ? 512 ? 245. Experimental results show that our achieved rendering rate is less dependent on viewing angles.