A New Structure--From--Motion Ambiguity

We demonstrate the existence of a new approximate ambiguity in structure from motion which occurs as generically as the bas{relief ambiguity but applies more strongly to scenes with larger depth variation. It occurs for moderate translations and eld of view (as for the bas{relief ambiguity) and applies to multi{frame, nite{motion sequences where the camera moves roughly along a line, as well as to optical ow. Previous work on the bas{relief ambiguity gave a partial characterization of the error sensitivities in recovering the camera heading, assuming that the scene was non{planar and that the heading was suuciently diierent from the view direction. Our analysis completes the understanding of the error sensitivities under these conditions.