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49 
Relative Accuracy 
se Bec Tae 
15 Initially the procedure was tested by bridging a strip of seven synthetic photo- 
graphs, The computed date for these i.e, tilts, flying heights and ground co-ordinates 
were mathematically correct, As the Stereogram solutions were done on desk computers 
with only 4 iterations slight residual 'K's! remained, these residuals being the main 
factors contributing to small errors in the results, 
Standard errors for the minor control points were as follows : 
i0,002 mm 
+0,23 feet 
+0.3 feet 
+0. feet 
  
Focal length was 6" and scale was 1:40,000, 
The followi 
relative results obtained on the Gordon Project, now in hand, give 
fair indication of 
1 . . 3 
he results which may be obtained, 
n 
4 
U 
  
  
  
  
   
  
  
Ths a 3 eo nbnaoins > y ; ze : c nd > 
This pro ect, e bracing about 2,000 square miles of country, is covered by ten 
cross strips, East and West, and three Key Strips. 
The three Keys and six cross strips have been adjusted to ground control to 
date, Four of these cross strips were combined in a block adjustment so that.plotting 
could be eommeneed as soon as possible, 
The length of a strip is approximately 50 miles and each Strip eontains an 
verage of 22 overlaps between terminal eontrol areas, 
n. As stated, all points were observed twice and if the range between readings ex- 
ceeded ,0O4 mm.the point was re-read, However on one film of the Gordon Project differen- 
ial distortion up to a maximum of 0,2 mm.in 10 mms. occurred, This made it necessary to 
observe to all four R au crosses instead of the nearest cross as is normally done. The 
best possibl iccurae s thus obtained, even so it was felt that the accuracy of the photo 
o-ordinates was still impaired, However overall accuracy of ihe final photo co-ordinates 
should be ++ \ 20:097 mms 
  
3. (a) Bridging from the initial. control area of a strip, the differences between the 
Cd Ao elemente f qi and + 
ridged ] n Lilt 1 those computed from the ground control for the final control 
Standard Error 
witudinal Tilt + 05'20" 
Lateral Tilt + 0755" 
    
rminal control areas and applying a linear adjustment to 
€ 
n, the differences between the bridged values and 
those computed from ground control on the middle control area were as follows :- 
  
sen ther 
  
  
Standard Error 
  
Longit inal Till i 05'20" 
Lateral Tilt + 01'145" 
rround trol (Eastings +2] yés. 
" M Northings) + 32 yds. 
, values for every photograph are derived by bridging between the 
,ained on the three control areas, Then bridging the flying height 
from the initial control area, the difference between the bridged flying height and the 
3 
flying height computed from ground control on the final control area was +75 feet. 
he (a) The final tilt 
solute tilt values obt 
  
  
(b) A value for the flying height of the middle control area was computed by bridging 
between the terminal controls and applying a linear adjustment to correct for the mis- 
closure between them, The difference between the bridged value and that computed from 
ground control on the middle control area was +Æ 3) feet, 
5. After the adjustment of the strips was carried out, ard prior to the block 
adjustment of the 4 runs previously referred to, a comparison was made between the strip 
tie poi: occurring midway between the three control areas of each strip where maximum 
residual errors would be expected to occur, 
The following results were obtained for 20 tie points.