Characterization and construction of helical polynomial space curves

  • Authors:
  • Rida T. Farouki;Chang Yong Han;Carla Manni;Alessandra Sestini

  • Affiliations:
  • Department of Mechanical and Aeronautical Engineering, University of California, Davis, CA;Department of Mechanical and Aeronautical Engineering, University of California, Davis, CA;Dipartimento di Matematica, Università di Roma "Tor Vergata", Via della Ricerca Scientifica, Roma 00133, Italy;Dipartimento di Energetica, Università di Firenze, Via Lombroso 6/17, Firenze 50134, Italy

  • Venue:
  • Journal of Computational and Applied Mathematics
  • Year:
  • 2004

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Abstract

Helical space curves are characterized by the property that their unit tangents maintain a constant inclination with respect to a fixed line, the axis of the helix. Equivalently, a helix exhibits a circular tangent indicatrix, and constant curvature/torsion ratio. If a polynomial space curve is helical, it must be a Pythagorean-hodograph (PH) curve. The quaternion representation of spatial PH curves is used to characterize and construct helical curves. Whereas all spatial PH cubics are helical, the helical PH quintics form a proper subset of all PH quintics. Two types of PH quintic helix are identified: (i) the "monotone-helical" PH quintics, in which a scalar quadratic factors out of the hodograph, and the tangent exhibits a consistent sense of rotation about the axis; and (ii) general helical PH quintics, which possess irreducible hodographs, and may suffer reversals in the sense of tangent rotation. First-order Hermite interpolation is considered for both helical PH quintic types. The helicity property offers a means of fixing the residual degrees of freedom in the general PH quintic Hermite interpolation problem, and yields interpolants with desirable shape features.