Abstract: Various embodiments of an apparatus, methods, systems and computer program products described herein are directed to a Trajectory Alignment Engine that generates within a unified three-dimensional (3D) coordinate space: (i) a 3D virtual medical model positioned according to a model pose, (ii) a virtual trajectory extending from a target point associated with a selected portion of the 3D virtual medical model and (iii) a dynamic navigation guide virtual object. The Trajectory Alignment Engine detects one or more changes in an instrument pose and/or an instrument position of a physical instrument in the 3D coordinate space. The Trajectory Alignment modifies the display of the dynamic navigation guide virtual object in the AR display at least in part on one or more of: the instrument pose changes and the instrument position changes.