Using Synthetic Images to Register Real Images with Surface Models
A number of image analysis tasks can benefit
from registration of the image with a model of 
the surface being imaged.  Automatic navigation using visible
light or radar images requires exact alignment 
of such images with digital terrain models.  In addition,
automatic classification of terrain, using 
satellite imagery, requires such alignment to deal correctly
with the effects of varying sun angle and 
surface slope.  Even inspection techniques for certain
industrial parts may be improved by this means. 
We achieve the required alignment by matching the real
image with a synthetic image obtained from a surface 
model and known positions of the light sources.  The
synthetic image intensity is calculated using the 
reflectance map, a convenient way of describing surface reflection
as a function of surface gradient. 
 We illustrate the technique using LANDSAT images and digital terrain models.
CACM November, 1978
Horn, B.K.P.
Bachman, B.L.
