  This paper deals with the error analysis of a novel navigation algorithm that
uses as input the sequence of images acquired from a moving camera and a
Digital Terrain (or Elevation) Map (DTM/DEM). More specifically, it has been
shown that the optical flow derived from two consecutive camera frames can be
used in combination with a DTM to estimate the position, orientation and
ego-motion parameters of the moving camera. As opposed to previous works, the
proposed approach does not require an intermediate explicit reconstruction of
the 3D world. In the present work the sensitivity of the algorithm outlined
above is studied. The main sources for errors are identified to be the
optical-flow evaluation and computation, the quality of the information about
the terrain, the structure of the observed terrain and the trajectory of the
camera. By assuming appropriate characterization of these error sources, a
closed form expression for the uncertainty of the pose and motion of the camera
is first developed and then the influence of these factors is confirmed using
extensive numerical simulations. The main conclusion of this paper is to
establish that the proposed navigation algorithm generates accurate estimates
for reasonable scenarios and error sources, and thus can be effectively used as
part of a navigation system of autonomous vehicles.
