Quartic Beta-splines

  • Authors:
  • Barry Joe

  • Affiliations:
  • Univ. of Alberta, Edmonton, Alb., Canada

  • Venue:
  • ACM Transactions on Graphics (TOG)
  • Year:
  • 1990

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Abstract

Quartic Beta-splines have third-degree arc-length or geometric continuity at simple knots and are determined by three &bgr; or shape parameters. We present a general explicit formula for quartic Beta-splines, and determine and illustrate the effects of varying the &bgr; parameters on the shape of a quartic Beta-spline curve. We show that quartic (and higher degree) rational Beta-splines with arc-length continuity satisfy the same continuity conditions as (nonrational) Beta-splines. We also show that the torsion continuous spline curves presented by Boehm ("Smooth Curves and Surfaces.” In Geometric Modeling: Algorithms and New Trends, G. E. Farin, Ed. SIAM, Philadelphia, Pa., 1987, pp. 175-184.) are equivalent to nonrational quartic Beta-spline curves, and determine the relationship between the shape parameters for the two types of curves. Finally, we present an algorithm for inserting a new knot and determining the refined control polygon.