Abstract: The proper topology structure is a key factor of the offset algorithm of a curve. An offset algorithm of B-spline curves is presented based on the key points on the offset curve. Firstly, the key points are computed by using self-adaptive sampling technique, then the self-intersected segments are discarded, and the proper topology structure is ensured. The algorithm has been applied in the business software OpenCAD.

Key words: computer application, offset algorithm, topology structure, B-spline curves