The traditional concepts considered that only off-plane displacement can be obtained by the shadow moire method, but the slope moire fringes must be obtained from the specimen with mirror surface by the reflection moire method, etc. However, our recent experimental results reveal that the off-plane displacement fringe and the slope fringe appear together in a shadow moire pattern under experimental definitions. The basic principle and related experiment techniques are presented firstly in this paper. Two examples, a thin hyperboloidal shell and a thin cylindrical shell with local buckling, are given to demonstrate the actual coupled moire fringe patterns. Moreover, two distribution curves of δ<i>W</i>/δ<i>x</i> and <i>W</i> along asymmetry axis on the thin hyperboloidal shell are also calculated.
According to the characteristic of the optical field arrangement, parallel illumination and parallel receiving in shadow moire method, that the reference grating and the shadow moire can be shifted equal distance at the same time, are proposed in this paper. First, the calculation formula for determining exact phase-shifting values and its experimental techniques were derived. Second, an exact simulation technique in shadow moire topography was constructed on the basis of the conceptions of geometrical interference mode for forming the virtual shadow moire fringes and the calculation formula of exact phase-shifting values. Third, to verify the validity of the calculation principle and simulation technique, the experimental results of the two typical models were offered, one was the cylinder and the other was sphere. These results indicate that the method proposed in this paper can improve the precision of three dimensional shape reconstructions and promote the development of shadow moire topography.