i^ 
& cross-hair superimposed in the viewing system is success- 
ively centered upon each image of each target. Linear trans- 
lation (i.e. x,y movement of the stage) is digitized by 
means of linear glass scales and optical encoders having 
a resolution of 1 micrometer (about 0.00004 inch).  Out- 
put is to punched paper tape in our hardware setup. 
Data Processing 
  
3.5.1 The Photogrammetric Reduction 
  
The photogrammetric triangulation procedure 
described in paragraphs 2.3 through 2.5 is embodied 
in a set of JFK-developed computer programs known 
as CRABS (Close Range Analytical Bundle Solution). 
Other than the photographic measurements from the 
comparator, input requirements of the programs are 
primarily limited to rough approximations of the 
X 
j^! 
j>2j coordinates of a few targets, similar 
approximations for the camera station locations and 
directions of the canera axes and a list of the 
target identification numbers. The approximations 
are used simply to "start" the solution which then 
iterates to convergence. There is, however, the 
need to carefully observe (manually) printed results 
of a quality control nature (for example, the 
measurement residuals described in paragraph 2.5.1). 
Once the. X.,Y Z coordinates of the targets 
i 
and their standard deviations were obtained the 
pure photogrammetric work was considered complete. 
Typically, the standard deviations were on the order 
of 1/32 inch. All remaining computations, though 
=17-