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