Selection of fiducial locations and performance metrics for point-based rigid-body registration

•A method is described to find optimum locations of fiducials for registration.•When N fiducials are optimally selected, extra fiducials are of limited benefit.•Different metrics are used to gauge the performance of registration.•Different fiducials configurations minimize different metrics.

A method is described to select the location and number of fiducials used in point-based, rigid-body registration of two coordinate frames. Two indices are introduced which are used to search for the optimum configuration of fiducials. They can be used to quickly evaluate a large number of configurations because no actual registration is involved in their calculation. Furthermore, configurations yielding small values of the indices correlate well with configurations which result in optimum registrations. Three registration performance metrics are discussed, and it is shown that optimization of different metrics leads to different selection of fiducial configurations. If an optimized configuration is selected as a starting configuration of N fiducials, the addition of extra fiducials does not significantly improve the registration in most cases. This work is based on 3D data acquired with three different instruments, each having different noise and bias characteristics.