Direct highlight line modification on nurbs surfaces

Reflection characteristics of surfaces, as visualized by highlight lines, are important design objectives in automotive styling. A method is presented that allows the direct modification of a highlight line on a NURBS surface. The algorithm presented will automatically adjust the control points of the NURBS surface resulting in a modified surface shape that produces the desired highlight line. A system of nonlinear equations is developed that expresses the relationship between NURBS control points and reference points on the highlight line. The inverse problem is solved through linearization by a first-order Taylor expansion. In addition, a shape control mechanism is introduced that distributes control point changes over the surface in a coherent and predictable way. With this mechanism, the user is able to interactively control the locality, or extent, of the surface modification while maintaining the desirable highlight line modification. (C) 1997 Elsevier Science B.V.