49 
Scale References 
  
Along with targetting of the ship-halves, the shipyard 
also fastened two 50-foot beans lin a vertical direction 
on each of the traverse sections to be mated. A target 
was attached near each end of each beam. After completion 
of the photographic work, the distance between each target 
pair along a beam was measured with a flat-wire band chain. 
These distances were used later to establish a true scale 
for the photogrammetric solution in the manner described 
in paragraph 2.4. 
While it may seem extreme to have attached beams to the 
mating faces, it must be recognized that photogrammetrically 
derived coordinates of targets will inherent a scaling 
error exactly equal to the error in determining the average 
scale factor over the reference distances. Hence, it is 
mandatory that very accurate reference distances be 
established. in order to obtain these accurate distances 
the measurements must be made with a good steel or invar 
tape and must not be contaminated by piecemeal measurements, 
physical obstructions such as weld beads, cambered surfaces 
on long unsupported lengths of the tape. 
To establish the accuracy required of the taped 
reference distances it must first be appreciated that the 
scale factor to be derived will include the error of the 
photogrammetrically triangulated coordinates of the targets 
defining each reference distance as well as error in the 
physical taping of the same distances. For Sun's ship 
  
lone toward the port side and one toward the starboard. 
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