BuL 3/1964
153
The Gigas-Zeiss Orthoprojector
by Dr.-Ing. M. Ahrend, Dr.-Ing. W. Brucklacher, Dr.-Ing. H.-K. Meier and H. Utz,
Oberkochen
1. Introduction
It is a well-known fact that any single aerial photograph, due to its perspective projection, will
represent the true map position of ground points only if the surface of the terrain is an ideal plane.
In this ideal case, the enlarged or (because of camera tilt at the instant of exposure) rectified prints
of aerial photographs would be perfectly equivalent to a conventional map, with the exception of
residual errors which are, however, insignificant in this particular case.
In all those cases in which there is relief in the terrain, the enlarged or rectified print of the aerial
photograph exhibits certain radial “deviations” from the true map position towards the nadir point
or away from it.
In stereophotogrammetry, these displacements give rise, among others, to so-called x-parallax. The
mechanical or numerical elimination of x-parallax in stereophotogrammetry leads to “error-free”
maps. In single-image photogrammetry, these deviations are responsible for residual errors in the
so-called “aerial mosaics”, the megnitude of which is illustrated by an example (Fig. 1). (This
example does not necessarily imply that it would be appropriate to perform a rectification in this
terrain and with the control points available).
(7) control-points H nadir-point ^ at scale 1:10000
Fig. 1 Theoretical example of residual errors in aerial mosaics. The example is based on an assumed photo
graph (flying height 3000 m) taken with a 6”*9 X 9” camera, rectified with reference to the four marginal
„control points” of identical elevation.
There are many purposes for which the accuracy of aerial mosaics — possibly increased by the
use of longer focal lengths or by partial rectification — is entirely sufficient. One of these is the large
field of general planning and development. The world-wide distribution of so-called photogrammetric
rectifiers, among which the German-made SEC V occupies a special position in many respects,