Quantifying the effect of a control point on the sign of curvature

We present a method for computing the domain, where a control point is free to move so that the corresponding planar curve is regular and of constant sign of curvature along a subinterval of its parametric domain of definition. The approach encompasses all curve representations that adopt the control-point paradigm and is illustrated for a quintic Bézier curve and a B-spline curve of degree 10.