High Precision Contouring with Moiré and Related Methods: A Review

Optical methods of contouring that utilise image recordings by cameras are based on a fundamental discipline, projective geometry. The 3-D world is projected in 2-D utilising a camera modelled in the technical literature by the pinhole camera. To get back 3-D information, the fundamental property measured is parallax. Parallax is a vector resulting from the difference of the projective coordinates of a point in space when projected onto a plane from two different points. The oldest method used for measuring parallax is photogrammetry. It is assumed to be the most precise technique, with the capability of obtaining 10-5 of the largest dimension of the measured object. This study summarises the state-of-the-art methods based on projecting a spatial carrier. Starting with the concept of moire as a form of photogrammetry, the different optical techniques for parallax determination are discussed. Although the moire method has reached 1 mu m accuracy in laboratory work, a question remains: can moire become a standardised contouring technique yielding 10-6 m accuracy This study is devoted to the analysis of high accuracy contour measurements, through both theoretical derivations and experimental verifications.