to- 
nt. 
ons 
his 
are 
ses 
len 
xa- 
| is 
T 
of 
lon 
pa- 
hat 
ive 
ens 
ral- 
ole. 
and 
  
As a consequence, some reservations have successively been inserted in 
the reviews. 
In 1957, an aerophotogrammetric survey has been carried out in Li- 
beria. Due to the special meteorological conditions in the Tropics, the 
author has had the luck to be faced with such strange problems connect- 
ed to the optical distortion that their solution could be excepted to make 
a contribution to the subject above mentioned. 
The tropical conditions proved to require the use of infra-red film 
that, during this time, often gave the only chance to get a picture at all. 
As no infra-camera was available, an infra-red filter had to be adapted 
to the existing camera. Of course, this combination gives pictures 
marred by an extreme lens distortion that obviously requires a close 
mathematical treatment. 
For this treatment a determination of the total lens distortion curve 
was necessary. That determination was carried out in two ways, on one 
hand by means of a laboratory test, on the other by use of the vertical 
parallax method. 
Due to the considerable non-correspondence between the two results, 
the laboratory test curve was approved as the basic material for the 
treatment in question, 
In the stereo-instrument, the lens distortion curve corresponds to an 
original position of the stereoscopical pictures — called the "theoretical 
O-position" by the author — i. e. the original position that for any arbi- 
trary point will give the exact horizontal and vertical parallaxes that 
correspond to the lens distortion in this point. However, the instrumen- 
tal operator is not aware of this "theoretical 0-position". He only ob- 
serves the existing p,-parallaxes in the orientation points of the six- 
point-scheme, and his aim will be to reduce them by means of the til- 
ting element ¢ to such a small amount as he can. But the insertion of 
this tilt will result in a model deformation, too. 
A theoretical treatment of this fundamental problem establishes that 
the residual vertical parallaxes alone cannot give any information of 
the lens distortion curve as they represent a “disturbed O-position” of 
the stereoscopic pair of pictures. The comparison between the two tests 
mentioned above may be considered as a practical criterium. 
1. Introduction 
In Liberia, the Liberian American-Swedish Minerals Company — 
abbreviated to LAMCO — in a joint venture with Bethlehem Steel Co 
is developing a mining project of important magnitude. The Nimba 
mountains, located in the northeastern part of the country, represent a 
deposit of iron ore of the highest quality. However, the iron ore has 
to be transported about 280 km straight across the country to the coast 
for shipping. Therefore a railroad is planned between the Nimba area 
3