Constrained shape scaling of multi-surface objects

A method to scale a multi-surface object while holding the shape and size of specific features (trimming curves) unchanged is presented. The new method includes an earlier version for a one-NURBS-surface object as a special case by considering more general objects and more general features. The constrained scaling process is attach-and-deform based. The new surface is constructed by attaching the original features to a scaled version of the given object. The attaching process requires several transformations and a deformation of the scaled object. The resulting object has the same features as the original object while reflecting the shape and curvature distribution of the scaled object. The presented approach maintains a NURBS representation for each component surface of the resulting object and hence, is compatible with most of the current data-exchange standards. Test results on several car body surfaces with trimming curves are included. The quality of the resulting surfaces is examined using the highlight line model.