Unifying C-curves and H-curves by extending the calculation to complex numbers

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

  • Affiliations:
  • State Key Lab. of Cad&CG, Mechanical Engineering Department, Zhejiang University, PR China;IWF Institute, Mechanical Engineering Department, Technical University Berlin, Germany;Electrical Engineering Department, Technical University Berlin, Germany

  • Venue:
  • Computer Aided Geometric Design
  • Year:
  • 2005

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Abstract

Recently, we found that the CB-splines that use basis {sint,cost,t,1} and the HB-splines that use basis {sinht,cosht,t,1} could be unified into a complete curve family, named FB-splines (Zhang and Krause, 2005). FB-splines are a scheme of what we call here F-curves. This paper explains that in the domain of complex numbers, the extended C-curves and extended H-curves are the same curves. Therefore, F-curves can be constructed in two identical styles, C and H. The C style is an extension of C-curves that uses sin and cos, and the H style is an extension of H-curves that uses sinh and cosh. Here the representations of F-curves are clearer and simpler. For real applications, the definitions, equations and main properties for the F-curves in different schemes (FB-splines, F-Bezier and F-Ferguson schemes) are introduced in details. F-curves are shape adjustable, and their curvatures on terminals can be any expected value between 0 and ~. They can represent the circular (or elliptical) arc, the cylinder, the helix, the cycloid, the hyperbola, the catenary, etc. precisely. Therefore, F-curves are more useful than C-curves or H-curves for the surface modeling in engineering.