US.A-2 PHOTOGRAMMETRIC ENGINEERING 
number of years it has been generally assumed that vertical aerial photography 
is the most efficient medium for topographic mapping. It has long been known 
however, that twin low-oblique photography has certain inherent advantages 
which should lead to increased accuracy and economy in the cost of control 
and compilation of detail. Twin low-oblique photography has never been fully 
exploited because of the lack of suitable plotting instruments for using it, espe. 
cially in the aero-triangulation phase. Most of the practical applications in the 
past have been confined to single models. It was obvious, therefore, that one 
of the first goals was to develop a satisfactory plotter for both horizontal and 
vertical aerotriangulation of twin photography. This objective was achieved in 
the Twinplex plotter (described below) and the way was opened for a complete 
twin low-oblique photography system for precise map compilation. Having 
accomplished this goal, there was immediately undertaken a complete investi- 
gation of all of the photogrammetric processes to determine wherein improve- 
ments could be made. Thus, a ‘new look” in photogrammetric instruments was 
developed at the U. S. Geological Survey. The following glimpses of the major 
items in our new look may be of interest: 
1. NEW LENSES AND CAMERAS 
The recent development of new cameras, possessing greatly improved me- 
chanical characteristics and equipped with high-resolution, low-distortion 
lenses, opens the way for improve- 
ment in both the photographic and 
geometric qualities of aerial photog- 
raphy. In order to obtain the maxi- 
mum benefit from these improve 
ments in camera characteristics, the 
Geological Survey has purchased a 
number of T-12 cameras (See Figure 1) 
equipped with Planigon lenses (based 
on the Topogon V designed by Herr 
Richter of Zeiss), for allotment to 
contractors on Geological Survey 
aerial photography projects. These 
cameras have been modified by the 
manufacturer to incorporate certain 
Fic. 1. T-12 aerial camera. desirable features, such as additional 
fiducial marks and a device which in- 
dicates vacuum failure at the platen, thereby making the resultant photography 
more efficient for mapping purposes. 
  
2. MULTI-COLLIMATOR CAMERA CALIBRATOR 
As a further step in controlling the characteristics of cameras used on Geo- 
logical Survey projects, the Survey has installed a multi-collimator camera cali- 
brator (See Figure 2), by means of which cameras belonging to either the 
Geological Survey or private contractors can be quickly and carefully tested 
with a minimum of lost time. The unique feature of this calibrator is that it 
permits stereoscopic measurements of the test plates, thereby refining the pro- 
cedure for evaluating camera performance. 
! Investigations were also made into non-instrumental aspects of the photogrammetric syste 
such as further studies of the geometry of aerial photography, the effect of lens distortions, C-factor 
analyses, and other procedural studies. While important, they will not be discussed herein because 
they are not within the scope of this paper.