Replacing NURBS surfaces with analytic surfaces based on isocurve characteristics in B-rep models

Abstract The topological and geometric information in B-rep models is essential for various applications, including feature recognition, design verification, and automatic tool path generation. In particular, representing surfaces using an analytic format offers advantages for utilizing geometric information such as surface type, axis of rotation, and radius. Models composed solely of non-uniform rational B-spline (NURBS) surfaces often have limitations in extracting this type of information. To address this issue, this study proposes a method for identifying and replacing NURBS surfaces that can be represented analytically. In the first step, the feasibility of substituting an NURBS surface with an analytic surface is determined by examining the characteristics of its isocurves. In the second step, an equivalent analytic surface is created and used to replace the existing NURBS surface. To validate the proposed method, surface replacement experiments were conducted on multiple test cases. The results showed that, among 10 176 NURBS surfaces identified for possible analytic replacement across 37 B-rep models, 9163 surfaces were successfully substituted in a stable manner. In addition, an experiment comparing feature recognition in the pre- and post-replacement models was conducted. As a result, none of the 12 design features were recognized in the pre-replacement model, whereas all were correctly detected afterward, confirming that the replacement process significantly enhances feature recognition accuracy.