1. A positioning system comprising: a pattern projector configured to project a 2- or 3-dimensional pattern onto a surface of an object positioned on a couch; a detector responsive to said projected 2- or 3-dimensional pattern and configured to generate a detection signal representative of a detected 2- or 3-dimensional pattern on said surface of said object; a pattern analyzing circuit connected to said detector and configured to generate a surface representation of at least a portion of said surface of said object based on said detection signal; a memory configured to store a reference surface representation of at least a portion of said surface of said object; a correction analyzing circuit configured to generate a correction signal representative of a discrepancy in at least one of position and posture of said surface representation relative said reference surface representation; and a light projector connected to said correction analyzing circuit and configured to project information representing said discrepancy in at least one of position and posture onto said object or a surface of said couch.