A new method to scale a trimmed NURBS surface while holding the shape and s
ize of specific features (trimming curves) unchanged is presented. The new
method is fix-and-stretch based: the new surface is formed by fixing select
ed regions of the given trimmed NURBS surface that contain the trimming cur
ves and stretching the remaining part of the surface to reach certain bound
ary conditions. The stretching process is performed using an optimization p
rocess to ensure that the resulting surface reflects the shape and curvatur
e distribution of the scaled version of the given surface. The resulting su
rface maintains a NURBS representation and, hence, is compatible with most
of the current data-exchange standards. The new approach is more robust tha
n a previous, attach-and-deform based approach (Zhang P, Zhang C, Cheng F.
Constrained shape scaling of trimmed NURBS surfaces. In: Proceedings of the
1999 ASME Design Theory and Methodology Conference. Las Vegas, Nevada, 199
9) in that it can tolerate scaling factors of bigger values (up to 2 in som
e cases). The new approach also guarantees that the features remain exactly
the same after scaling. Test results on several car parts with trimming cu
rves and comparison with the previous approach are included. The quality of
the resulting surfaces is examined using the highlight line model. The pre
sented technique is important for integrating standard parts into a sculptu
red product. (C) 2000 Elsevier Science Ltd. All rights reserved.