In this paper we discuss two problems. One problem is: how to approximate the rolling ball blend by a series of bicubic patches? The other problem is: what to do if the rolling ball blend surface is self intersecting?
"Rolling ball blends and self-intersection", Proc. SPIE 1830, Curves and Surfaces in Computer Vision and Graphics III, (1 November 1992); doi: 10.1117/12.131744; https://doi.org/10.1117/12.131744