Embodiments consistent with the present disclosure allow the ring, arc, and linear offset values for a stereotactic frame to be determined for a cranial procedure without requiring a CT scan to be acquired with the fiducial frame attached. Having the ring, arc, and offset values available for a cranial procedure allows the surgeon to revert to traditional stereotactic ring-arc frame guidance as a fallback strategy in case a robot cannot be used. This disclosure also provides an alternate method for registering a ring-arc system to the medical image volume for facilities having no CT scanner or scanner with limited field of view such that the intended fiducial localizer cannot be used.