Moiré topography.
Using geometrical optics, an oblique-shadow method is shown to generate moiré patterns, which under specific conditions can be interpreted as contour lines of the surface. The oblique-shadow method consists of illuminating a viewing grid with equal spaced parallel lines. The light can be either a point source or parallel light, the observation point can be either at finite distance or at infinity. Conditions for which moiré patterns become contour lines of the surface are given.
Chiang
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