**Baten 1995 : **Methods
for extracting in real time the surface structure in a certain look-ahead range
from image sequences while driving are reviewed. Low spatial frequency
elevation profiles of roads are the only ones successfully recovered in
real-time up to now. Low frequency means that the characteristic geometrical
dimension for curvature estimation is at least an order of magnitude larger
than the axle distance of the vehicle carrying the camera. For the more general
case of a surface with relatively high spatial frequencies, an approach for
real-time recognition is proposed which separates low, medium and high spatial
frequency components; these components are estimated in a sequential,
iteratively parallel manner. The formulation of the approach is given.