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INSTRUMENTATION FOR INTEGRATED PHOTOGRAMMETRIC SYSTEM  U.S.A.—5 
  
Fic. 5. ER-55 projector set up for transverse photography. 
provide efficient and brilliant illumination of twin low-oblique photography 
used for aerotriangulation. 
6. ASPHERIC PLATE DIAPOSITIVE PRINTERS 
One of the primary problems in connection with printing diapositive plates 
isthe method used for compensating aerial-camera lens distortion. The Geologi- 
cal Survey's solution in the case of Multiplex diapositive printers consisted of 
using a printer lens having, as nearly as possible, an equal and opposite distor- 
tion pattern to that of the aerial camera lens. The difficulty with this kind of 
solution is that unless the aerial camera lens and the printer lens are in close 
agreement with respect to distortion characteristics, there will be residual errors. 
The same situation arises in the use of the Kelsh plotter if the diapositives 
are made by contact printing, and the distortion is compensated by the use of 
cams which vary the principal distance of the projector in accordance with the 
location in the model of the detail being plotted. Unless the cams are matched 
precisely to the lens distortion pattern, there will be residual errors from this 
source, 
The new approach by the Geological Survey was to develop high-resolution 
rinters utilizing aspheric correction plates for compensating aerial-camera 
distortion (See Figure 6). Negotiations for such a printer were started in 1948. 
À set of correction plates having varying corrections in accordance with the 
range of variations in camera lenses of a given type provides a means of match- 
Ing the printer compensation with the aerial-camera distortion more closely. 
The Geological Survey has designed and procured new-type projection diaposi- 
tive printers of this nature for use with ER-55 projectors, Kelsh plotters, and 
Multiplex projectors. The printer for the Kelsh plotter, being one-to-one, can 
be used with other plotters using full-size diapositives. 
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T. VARIABLE-RATIO PANTOGRAPHS 
In order to effect economies in the stereocompilation phase, a recent devel- 
opment of the Geological Survey has been the introduction of stereocompilation 
procedures involving scribing techniques and compilation work at scales at or