In an image that is an orthographic projection of a scene (an orthographic
image), image coordinates can be directly equated to scene coordinates.
However, we cannot geometrically derive the coordinate of a scene point
from the
coordinates of the corresponding image point.
An orthographic image will contain depth information if it can be
interpreted to be an image of a scene where . Depth then has
one degree of freedom. Note that this representation of depth is only
appropriate to scenes in which all visible surfaces are opaque.
In practice, a depth (or range) image can be created using a range finder.