Full-Field 3D Shape Measurement of Specular Surfaces by Direct Phase to Depth Relationship

This paper presents a new Phase Measuring Deflectometry (PMD) method to measure specular object having
discontinuous surfaces. A mathematical model is established to directly relate absolute phase and depth, instead of phase
and gradient. Based on the model, a hardware measuring system has been set up, which consists of a beam splitter to
change the optical path, and two LCD screens to display the same sinusoidal fringe patterns. By using model-based and
machine vision method, system calibration is accomplished to provide the required parameters and conditions. The
verification tests are given to evaluate the effectiveness of the developed system. The 3D shape of an artificial step
having multiple specular surfaces and a concave mirror has been measured. Initial experimental results show that the
proposed measurement method can obtain 3D shape of specular objects with discontinuous surface effectively.