A high-performance method for calculating the minimum distance between two 2D and 3D NURBS curves

We present a fast, accurate, and robust method to compute the minimum distance between two 2D and 3D NURBS curves. This is carried out by first decomposing both of the NURBS curves into their piecewise-Bézier forms. Candidate pairs, as a subset of all possible pairs, are extracted based on a two-level selection process. The first-level selection uses upper-lower bounds of Bézier subcurves to remove pairs. The second-level selection is based on the spatial relationship test between a pair of Bézier curves. An iterative multidimensional Newton-Raphson method is applied on all candidate pairs in order to calculate the approximate local minimum distances. Finally, by comparing all local minimum distances between a pair of Bézier subcurves, we are able to find the global minimum distance. The accuracy is improved by further use of the multidimensional Newton-Raphson method to give high accuracy. Source code is available online.