Establishing True Scale 
  
Inasmuch as the exposure station locations are not 
presurveyed, the solution described above cannot be 
performed at exact true scale. Instead, it is solved at 
an approximate true scale by holding two camera station 
locations fixed at their estimated locations. Afterwards, 
it is necessary to rescale computed target coordinates 
Xj>Yj 2j by that scale factor which will bring the 
approximate scale to exact true scale. 
To allow a determination of this scale factor it is 
customary to physically tape distances between several 
pair of targets on the object at the time photographs 
are being taken. - The corresponding distances are later 
computed from coordinates of the same targets as determined 
in the approximately scaled photogrammetric solution. The 
ratio of a taped distance divided by the calculated 
distance gives the scale factor for one target-pair. The 
average scale factor over all target pairs between which 
distances were physically taped is used to bring the 
approximate solution to exact true scale. 
Error Analyses 
  
As mentioned in section 2.3, the entire system of 
photogrammetric equations is solved according to the 
method of "least squares". Two distinct advantages 
of any least squares solution are that there is only 
one answer and standard deviations of all computed 
values are obtained as an automatic by-product. It is 
well to mention too, that under the assumption that all