A method includes controlling a robotic arm extending from a base in a free mode during a registration procedure and optically tracking the base and a marker mounted on the robotic arm during movement of the robotic arm in the free mode. The movement of the robotic arm causes movement of the marker without affecting a position of the base. The method also includes defining a coordinate transformation based on a position of the base and a plurality of tracked positions of the marker achieved during the movement of the robotic arm in the free mode and controlling the robotic arm using the coordinate transformation.

A method includes controlling a robotic system using a virtual boundary and based on optical tracking of a tracker, detecting a condition in which an optical detection device is occluded from detecting the tracker, and maintaining the virtual boundary if the condition persists for shorter than a predetermined period of time.

Provided is a system for positioning an intermediate head clamp (300) on a subject for medical interventions on the subject comprising a superior positioning cap (200) configured for placement on a head of the subject having a domed receiving space (222) for receiving a part of the head of the subject, provided with a plurality of adjustable protrusions (260, a, b, c, d, e) to adjust a pose of the superior positioning cap (200); an inferior positioning support (400) comprising a main body (410) configured for placement around the head of the subject in a region and a plurality of locating bodies (460, 470, 480) each for locating in and engaging with a bodily recesses to adjust the pose of the inferior positioning support (400); wherein the superior positioning cap (200) and inferior positioning support are configured to flank and each engage with the intermediate head clamp (300) such that intermediate head clamp (300) is rotatable around an axis of rotation co-axial with the axes of reference (250, 450) of the superior positioning cap (200) and of the inferior positioning support (400).