3047	 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. Image registration synthetic images surface models automatic hill shading digital terrain models image transformation image matching shaded images
