Abstract: A method for generating a composite terrain map, proceeding from an overview taken at relatively high altitude and photographs taken at relatively low altitudes, generates a composite terrain map that is relatively free of step irradiance variations where the photographs taken at relatively low altitudes are splined. Digitized representations of orthographic projections of the overview and each of the lower-altitude photographs, as regularly sampled in two orthogonal dimensions and referred to a common spatial frame of reference, are generated. The digitized representations of the orthographic projections of each of said photographs taken at relatively low altitudes are hig-pass spatially filtered, to generate digitized high-spatial-frequency responses. The digitized high-spatial-frequency responses are splined to generate a digitized high-spatial-frequency response for the composite terrain map.