Extending cubic uniform B-splines by unified trigonometric and hyperbolic basis

  • Authors:
  • Jiwen Zhang;Frank-L. Krause

  • Affiliations:
  • State Key Lab. of Cad & CG, Zhejiang University, PR China;IWF & IPK. Technical University Berlin, Germany

  • Venue:
  • Graphical Models
  • Year:
  • 2005

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Abstract

In this paper, the trigonometric basis {sin t, cos t, t, 1} and the hyperbolic basis {sinh t, cosh t, t, 1} are unified by a shape parameter C (0 ≤ C C2 continuity, and can represent elliptic and hyperbolic arcs exactly. They are adjustable, and each control point bi can have its unique shape parameter Ci. As Ci increases from 0 to ∞, the corresponding breakpoint of bi on the curve is moved to the location of bi, and the curvature of this breakpoint is increased from 0 to ∞ too. For a set of control points and their shape parameters, SB-spline and FB-spline have the same position, tangent, and curvature on each breakpoint. If two adjacent control points in the set have identical parameters, their SB-spline and FB-spline segments overlap. However, in general cases, FB-splines have no simple subdivision equation, and SB-splines have no common evaluation function. Furthermore, FB-splines and SB-splines can generate shape adjustable surfaces. They can represent the quadric surfaces precisely for engineering applications. However, the exact proof of C2 continuity for the general SB-spline surfaces has not been obtained yet.