Reversible watermarking of NURBS-based CAD models

We present an algorithm for embedding robust reversible watermarks into CAD models that are represented by a collection of NURBS (Non Uniform Rational B-Spline) surface patches. Changes to the geometry of the surface representation are introduced by moving one control point per surface patch. This approach provides robustness against converting the model into the mesh representation. The information needed to restore the original control point location is added to the knot vector of the patch, thus enabling recovery of the original model from the watermarked NURBS representation. We exploit the properties of the NURBS representation for preserving the continuity between adjacent patches. Continuity is the major criterion of designers for assessing the quality of surface models.