To illustrate this point, take Figure 1 as an example, 
but assume that there are really four photographs rather 
than two (which would be more apt to be the case in 
practice). Also assume that there are 300 targets on the 
object and that all targets are imaged on all photographs. 
For observed values we will have all photographic measure- 
ments Xjj,Yij which total 2,400 (2 measurements per image 
x 300 images per photograph x 4 photographs). For 
unknowns we will have the locations of the exposure 
stations and the directions of the camera axes which 
total 24 (6 unknowns per photograph x 4 photographs) plus 
the 900 unknown coordinates of the targets (3 coordinates 
per target x 300 targets). All told there will be 2,400 
equations containing only 924 unknovns -- a system over 
determined by a factor of 2.6) 
An interesting feature of this solution has a very 
important practical impact insofar as on-site work 1s 
concerned. Even though we are really interested only in 
calculating the X.,Y 
j Ze coordinates of each target, we 
3 9 
are also calculating the locations of the exposure 
stations and the directions of the camera axes at the 
same time. The ramification here is that it is totally 
unnecessary to pre-survey exposure station locations or 
to pre-determine camera pointing directions except in a 
very nominal sense so as to obtain the desired photo- 
graphic coverage.