A method and apparatus are provided wherein a moving light source is passed over a surface whose shape is to be determined, in two orthogonal paths and is fixed at a plurality of positions along each path such that the light source illuminates the surface at a different slope for each position. A binary image camera photographs the surface for each of the fixed positions and the point at which each of a plurality of points on the surface is first illuminated and last illuminated, as well as the points that last shadowed or last failed to shadow any given point, are recorded. Constraint equations develop the effect a given point has on its last and failing shadowers and the effect each last and failing shadower has on the given point. Upper and lower bounds of these points are iteratively re-calculated according to the constraint equations until none of the points exhibit any more change in their upper and lower bounds.