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,