Systems and methods for accurate determination of the position of an anatomic part of a subject in robotic assisted image-based surgery, using an inertial measurement unit (IMU) to determine the position and orientation of the anatomical part of the subject. The intrinsic drift of the IMU, which would make the IMU position measurements inaccurate, can be reset to zero regularly, at points of time when the subject's body is stationary. This can be achieved when motion from the subject's breathing and from the heartbeat are essentially zero. Such positions occur respectively when the respiratory signal shows the position of the breathing cycle to be at the end of the expiration phase, and the heartbeat signal represents a time in the diastole period of the subject's electrocardiographic cycle. When these two signal moments coincide, the IMU is essentially stationary, and its drift reset to zero.