  Obtaining complete information about the shape of an object by looking at it
from a single direction is impossible in general. In this paper, we
theoretically study obtaining differential geometric information of an object
from orthogonal projections in a number of directions. We discuss relations
between (1) a space curve and the projected curves from several distinct
directions, and (2) a surface and the apparent contours of projections from
several distinct directions, in terms of differential geometry and singularity
theory. In particular, formulae for recovering certain information on the
original curves or surfaces from their projected images are given.
