7Coquillart S.Computing offsets of B-spline curves[J].Computer Aided Design,1987,19(6):305-309.
8Elber G,Cohen E.Error bounded variable distance offset operator for freeform curves and surfaces[J].International Journal of Computational Geometry and Application,1991,1(1):67-78.
9Lee I K,Kim M S,Elber G.Planar curve offset based on circle approximation[J].Computer Aided Design,1996,28(8):617-630.