A note on two-sided holes in implicit quadric spline surfaces

Some implicit spline surface schemes require filling two-sided holes [Dahmen 1989; Guo 1993] and a blending technique of Warren (1987) can be used to fill two-sided holes in quadric spline surfaces. This note shows that there are important cases where the blending technique does not apply. These cases are identified and an applicatble technique is proposed.