System Calibration Procedure 
A selection was.made of 39 gridpoint inter- 
sections in the gridplate replica, which were 
as symmetrically placed as was allowed by the 
arrangements of gaugeblocks on that replica 
at that time. This arrangement is shown in 
Fig 6, being a contact-scale stereogram of 
the calibration body. Observations were recor- 
ded on each of the selected 39 gridpoints and 
on each of the visible surfaces of the gauge- 
blocks. 
The observations on the gaugeblocks were used 
simply to determine a relationship between the 
planimetric and the height scales of the af- 
fine model. The gridplate observations were 
"adjusted to control" taking the planimetric 
coordinates of the selected points to vary 
both in X and Y between 200 and 400 mm and 
attributing a Z value throughout of 200 mm. 
The observations were recorded automatically 
in the PDP 11/34 which is online to the WILD 
A.10 Autograph. These observations were fed 
into the Department's Cyber 172 computer, 
along with the control values, using a stan- 
dard photogrammetric adjustment programme to 
compute the standard deviations of the obser- 
vation series and to list the residuals. 
The results of this calibration study are 
tabulated in Table 1. It may be seen that the 
difference between the planimetric and the 
height scales is quite small, suggesting that 
the principal distance adopted for the resti- 
tution of the model was close to that of the 
image acquisition system, meaning that the 
affine deformation was almost negligible. 
The standard deviations in X and Y, respec- 
tively of 0.11 and 0.15 mm in the scale of 
the obejct photographed, seem quite appropri- 
ate. The standard deviation in Z, of 0.43 mm 
might suggest that the gridplate replica, which 
was produced on a dimensionally stable film 
but was not held down by such a device as a 
vacuum frame,may not have been very flat. 
However, The objective was to develop a method 
and procedure which may warrant refinement, 
not to come up with an ultimate answer at the 
first attempt. 
TABLE 1 
  
ORIENTATION ELEMENTS: 
INSTRUMENTAL SETTINGS ON WILD A.10 AUTOGRAPH, 
FOR OBSERVATION OF CALIBRATION BODY NEGATIVES 
2 & 3. 
PRINCIPAL DISTANCE: 160 mm. BASE: 30 mm 
MODEL SCALES: X,Yys 1:2.23. 2: 1:2.33. 
Z conversion factor: 0.958. 
Z conversion multiplier: 
0.43, to read mm. 
Kappa. Phi. Omega. 
L.H. 99.88 97.490 100.00 
R.H. 99.91 102.329 100.00 
p. = 30.00 b - 0.00 p - 190.09 
x y Z 
(The Z range for the observations was about 
400 mm.) 
  
DATA REGARDING CALIBRATION BODY AND NEGATIVES: 
Gridplate dimensions in replica: 200 x 200 mm 
Replica dimensions in negative: 36.65 x 36.70mm 
Approximate negative scale is thus: 1:5.45. 
  
(It is to be noted that the stereogram used 
for the observation of the calibration body 
comprised one "central" Photograph and one 
photograph tilted through about four degrees. 
The convergence measured by the difference 
between the phi settings of the left-hand and 
right-hand projectors of the A.10 is 4.839 
grades.) 
  
  
  
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