the same. Any slight inconsistencies are due to the fact that for 
the relative orientation solution the X component of the exposure 
station is fixed and therefore adds nothing to the point selection 
computations. 
For che triplet relative orientation there were 45 image points 
in each model, that is an 81 point symmetrical pattern on the center 
photograph. Two different cases are shown. In the first case, the 
center photograph and the X component of the exposure station of 
the third photograph were fixed. A typical example of the selection 
process under these circumstances is shown in Figure 6. The nine 
triangular symbols indicate the points used for the initial relative 
orientation solution, while circular symbols are used for candidate 
points. The zones which are marked in Figure 6 indicate the ordering 
of areas for optimum measurements. Each individual stereopair model 
in the triplet shows the characteristics of the single stereopair 
solution. In Figure 7 is plotted the selection criterion versus the 
number of measurements added to the solution. 
In the second case, the first photograph and the X component of the 
exposure station of the second photograph are fixed. Under these 
conditions, and using the same data as in the previous example, the 
selection procedure yields the zones of selection as depicted in 
. Figure 8. 
  
FIGUI