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The solar periscope, introduced to photogrammetry many 
  
years ago, produces accuracies comparable to that achieved by 
horizon camera. It requires a quite elaborate installation in 
the aircraft and is also dependent on atmospheric conditions. 
But to the best of the author's knowledge, it has not been used 
during the past four years on practical mapping projects. 
Systems employing gyroscopes, which may form part of an 
inertial guidance system, for determination of tip and tilt or 
  
stabilization of aerial cameras, show promise of fulfilling the 
needs of vertical aerial triangulation, 
The A.N.Q.-28 system developed in the U.S.A. gives position 
  
and orientation elements of the aerial camera at the moment of 
exposure as well as APR data. But the acquisition and operating 
costs of this system place it far beyond the reach of civilian 
agencies and seriously questions the economy of the system.  Out- 
side of the results of initial evaluations carried out over test 
areas several years ago very little has been heard since about 
the performance of the system on practical projects, and about 
the use made of auxiliary data in adjustment of aerial triangu- 
lation, provided by this system. 
The specifications for the Litton LTN-51 Inertial Navigation 
  
System list the following accuracies of pitch, roll and heading 
for ranges of 0 to 159: 4 0,29: QJ 4:0,2?; X + 0.49. These 
accuracies are lower than those obtainable by horizon camera or 
solar periscope. It can be reasonably expected that when this 
system is coupled to an aerial camera to register the orientation