Three-dimensional profilometry by symmetrical fringes projection technique

A precise interferometric method for three-dimensional surface measurements in a wide dynamic range is presented. The method is based on symmetrical two-spacing projection phase-stepping interferometry. Two approaches are proposed—one with double symmetrical illumination and the other with double symmetrical observation—which reduce influence of shadowing at investigation of complex surfaces and allow absolute coordinates estimation. The theoretical background, experimental check as well as accuracy and sensitivity assessment of the method are discussed. The proposed technique is especially useful for remote, non-destructive in-situ measurements of real objects—for example historical objects and monuments.