UC Davis

A rotation–minimizing frame (f1,f2,f3) on a space curve r(ξ) defines an orthonormal basis for ℝ3 in which f1= r′/ | r′| is the curve tangent, and the normal–plane vectors f2, f3 exhibit no instantaneous rotation about f1. Polynomial curves that admit rational rotation–minimizing frames (or RRMF curves) form a subset of the Pythagorean–hodograph (PH) curves, specified by integrating the form r′(ξ)=A(ξ)iA∗(ξ) for some quaternion polynomial A(ξ). By introducing the notion of the rotation indicatrix and the core of the quaternion polynomial A(ξ) , a comprehensive characterization of the complete space of RRMF curves is developed, that subsumes all previously known special cases. This novel characterization helps clarify the structure of the complete space of RRMF curves, distinguishes the spatial RRMF curves from trivial (planar) cases, and paves the way toward new construction algorithms.