Abstract: A new method is presented to determine the fitting direction while using Dr.Bridge′s linear editor to model various parabolas in this paper. By considering convex-concave property at monotone interval of a quadratic curve, four different parabola shapes with two controlling points fitted, are provided. Based on the method, two sets of symbols are introduced to describe the monotonicity and convex-concave property of parabola. And the identification of parabola fitting direction is presented, which explores a new way to fit a parabola by two controlling points when linear editor of Dr.Bridge is used. The presented method is suitable for determining the parabola fitting direction whether parabola is fitted by two or by three controlling points. The method is illustrated by its simplicity and convenience, and efficient for program realization, which greatly promotes the modeling efficiency.

Key words: parabola fitting; controlling point; monotonicity; convexconcave property; linear editor