than 10 micrometers (0.00040 inch) and as a group 
have a root-mean-square value of 1.5 to 3 micrometers 
(0.00006.t0.0.00012 inch) on the original .photo- 
graphs. 
Standard Deviations 
  
Standard deviations of computed x, +15 +74 
coordinates are obtained from the least 
squares solution without significant extra 
Y Z2. themselves. 
effort beyond obtaining the X j'?j 
j> 
The fact that each and every coordinate will 
have a unique standard deviation is probably 
intuitive in that it must be s function of the 
number.of rays intersecting a point, the lack of 
intersection of all rays (which is manifested 
in the measurement residuals), the geometry 
(included angles of intersection) of the incoming 
rays: to.the point,the focal length. of the camera 
and the dístances from the camera stations to 
the point. All of these factors are implicitly 
taken into account in the standard deviations 
which come as a by-product of the least squares 
solution. 
Fit to Reference Distances 
  
A third measure of quality of the photogrammetric 
solution and one which is more readily obvious to 
the non-photogrammetrist is the final "fit" to the 
scale reference distances (see paragraph 2.4). After 
scaling the photogrammetric solution by the average 
scale factor, the individual scale reference distances 
may be recomputed using the scaled photogrammetric 
wi]