This article examines the computational problems underlying the 3-D interpretation of surface contours. A surface contour is the image of a curve across a physical surface, such as the edge of a shadow cast across a surface, a gloss contour, wrinkle, seam, or pigmentation marking. Surface contours by and large are not as restricted as occluding contours and therefore pose a more difficult interpretation problem. Nonetheless, we are adept at perceiving a definite 3-D surface from even simple line drawings (e.g. graphical depictions of continuous functions of two variables). The solution of a specific surface shape comes by assuming that the physical curves are particularly restricted in their geometric relationship to the underlying surface. These geometric restrictions are examined.
