A method for determining three-dimensional position information of a surface of an object, the method comprising: projecting a fringe pattern from a pair of optical fibers (14A, 14B) to illuminate a surface of an object, the fringe pattern being generated by the interference of optical radiation emitted from each of the optical fibers, the radiation emitted from each optical fiber being coherent with respect to the radiation emitted from the other optical fiber; monitoring the location of one fringe in the fringe pattern, by sampling a portion of the fringe pattern using an optical element disposed between the object and the exit ends of the first and second optical fibers, to determine a displacement error of the fringe pattern; adjusting a phase of the optical radiation emitted from one of the optical fibers relative to a phase of the optical radiation emitted from the other optical fiber to substantially cancel the displacement error and stabilize the fringe pattern; detecting optical radiation scattered from the illumination of the surface of the object with the fringe pattern; changing a phase of the optical radiation emitted from one of the optical fibers relative to the phase of the radiation emitted from the other optical fiber to cause a predetermined phase shift in the fringe pattern; detecting optical radiation scattered by the surface of the object after the predetermined phase shift in the fringe pattern; and calculating three-dimensional position information of the surface of the object in response to the change of the phase to cause the predetermined phase shift in the fringe pattern and in response to the optical radiation detected before and after the predetermined phase shift in the fringe pattern. projecting a fringe pattern from a pair of optical fibers (14A, 14B) to illuminate a surface of an object, the fringe pattern being generated by the interference of optical radiation emitted from each of the optical fibers, the radiation emitted from each optical fiber being coherent with respect to the radiation emitted from the other optical fiber; monitoring the location of one fringe in the fringe pattern, by sampling a portion of the fringe pattern using an optical element disposed between the object and the exit ends of the first and second optical fibers, to determine a displacement error of the fringe pattern; adjusting a phase of the optical radiation emitted from one of the optical fibers relative to a phase of the optical radiation emitted from the other optical fiber to substantially cancel the displacement error and stabilize the fringe pattern; detecting optical radiation scattered from the illumination of the surface of the object with the fringe pattern; changing a phase of the optical radiation emitted from one of the optical fibers relative to the phase of the radiation emitted from the other optical fiber to cause a predetermined phase shift in the fringe pattern; detecting optical radiation scattered by the surface of the object after the predetermined phase shift in the fringe pattern; and calculating three-dimensional position information of the surface of the object in response to the change of the phase to cause the predetermined phase shift in the fringe pattern and in response to the optical radiation detected before and after the predetermined phase shift in the fringe pattern.