A system for obtaining three-dimensional information about a surface having a set of at least one reference target (306, 413, 513), each reference target (306, 413, 513) being provided at a fixed position one of on an environment of said surface and on said surface, said system comprising: a sensing device (200, 601) having: a pattern projector for providing a projected pattern (305, 416, 516) 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 (306, 413, 513) of said set of reference targets (306, 413, 513) and at least a portion of said projected pattern (305, 416, 516) 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 (517, 604) of the projected pattern (305, 416, 516) and target contours from said 2D image; a 3D surface point calculator for calculating 3D coordinates of the surface points (517, 604) from said 2D image coordinates of said surface points (517, 604) using said calibration data; a 3D target calculator (611, 710) for calculating, from said 2D image coordinates of said target contours (610, 702), using said 3D coordinates of the surface points and said calibration data, at least one of a 3D position (612, 703) and an actual orientation for said reference target in a sensor coordinate system; said system thereby being adapted to perform the steps of: identifying neighboring surface points (517, 604) located around said target (306, 413, 513) using said 2D image coordinates of said target contours (610,702); calculating 3D coordinates of the neighboring surface points (517, 604) in said sensor coordinate system calculated from said 2D image coordinates of said surface points (517, 604) using said calibration data; fitting a surface section model on said 3D coordinates of said neighboring surface points (517, 604) calculated in said sensor coordinate system; and using said fitted surface section model, at least one of: refining an estimated 3D position into the 3D position in said sensor coordinate system; and identifying the actual orientation of said target. a sensing device (200, 601) having: a pattern projector for providing a projected pattern (305, 416, 516) 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 (306, 413, 513) of said set of reference targets (306, 413, 513) and at least a portion of said projected pattern (305, 416, 516) is apparent on said 2D image; a pattern projector for providing a projected pattern (305, 416, 516) 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 (306, 413, 513) of said set of reference targets (306, 413, 513) and at least a portion of said projected pattern (305, 416, 516) 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 (517, 604) of the projected pattern (305, 416, 516) and target contours from said 2D image; a 3D surface point calculator for calculating 3D coordinates of the surface points (517, 604) from said 2D image coordinates of said surface points (517, 604) using said calibration data; a 3D target calculator (611, 710) for calculating, from said 2D image coordinates of said target contours (610, 702), using said 3D coordinates of the surface points and said calibration data, at least one of a 3D position (612, 703) and an actual orientation for said reference target in a sensor coordinate system; said system thereby being adapted to perform the steps of: identifying neighboring surface points (517, 604) located around said target (306, 413, 513) using said 2D image coordinates of said target contours (610,702); calculating 3D coordinates of the neighboring surface points (517, 604) in said sensor coordinate system calculated from said 2D image coordinates of said surface points (517, 604) using said calibration data; fitting a surface section model on said 3D coordinates of said neighboring surface points (517, 604) calculated in said sensor coordinate system; and using said fitted surface section model, at least one of: refining an estimated 3D position into the 3D position in said sensor coordinate system; and identifying the actual orientation of said target. identifying neighboring surface points (517, 604) located around said target (306, 413, 513) using said 2D image coordinates of said target contours (610,702); calculating 3D coordinates of the neighboring surface points (517, 604) in said sensor coordinate system calculated from said 2D image coordinates of said surface points (517, 604) using said calibration data; fitting a surface section model on said 3D coordinates of said neighboring surface points (517, 604) calculated in said sensor coordinate system; and using said fitted surface section model, at least one of: refining an estimated 3D position into the 3D position in said sensor coordinate system; and identifying the actual orientation of said target.