Photographic Products
Photographic products are derivatives of single photographs or composites of overlapping photographs. Fig. 1.4 depicts the typical case of photographs taken by an aerial
camera. During the time of exposure, a latent image is formed which is developed to
a negative. At the same time diapositives and paper prints are produced. Enlargements
may be quite useful for preliminary design or planning studies. A better approximation
to a map are rectifications. A plane rectification involves just tipping and tilting the
diapositive so that it will be parallel to the ground. If the ground has a relief, then the
rectified photograph still has errors. Only a differentially rectified photograph, better
known as orthophoto, is geometrically identical with a map.
Composites are frequently used as a first base for general planning studies. Photomosaics are best known, but composites with orthophotos, called orthophoto maps are
also used, especially now with the possibility to generate them with methods of digital
photogrammetry.