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.