1. A system for obtaining three-dimensional information about a surface having a set of at least one reference target, each reference target being provided at a fixed position one of on an environment of said surface and on said surface, said system comprising: a sensing device having: a pattern projector for providing a projected pattern on said surface; a camera for acquiring a 2D image of said surface from a viewpoint, said camera cooperating with said pattern projector, wherein at least one target of said set of reference targets and at least a portion of said projected pattern is apparent on said 2D image; a storage for calibration data, said calibration data including extrinsic and intrinsic parameters of said camera and said pattern projector; an image processor for extracting 2D image coordinates of surface points of the projected pattern and target contours from said 2D image; a 3D surface point calculator for calculating 3D coordinates of the surface points from said 2D image coordinates of said surface points using said calibration data; a 3D target calculator for calculating, from said 2D image coordinates of said target contours, using said 3D coordinates of the surface points and said calibration data, at least one of a 3D position and an actual orientation for said reference target.