5; Calibration principal distance. 
6. Centre of symmetry. 
7. Reseau datum cross. 
The origin of measurements and the sign convention used should also 
be defined in this section. A suggested layout is given in Appendix |. 
The second section should give practical details and a standardised 
procedure for undertaking calibration. This should go into considerable 
detail to ensure that measurements made throughout the world are really 
comparable. Ideally only one method should be advocated but at present 
this would impose hardship on some manufacturers and in some countries 
where the necessary specialised equipment is not available. Accordingly, 
more than one method may be described, perhaps both a visual and a photo- 
graphic method, with a rider to the effect that one method is preferred 
to the other. Then any laboratory wishing to set up new equipment would 
be guided in its choice, while existing equipment would not need to be 
scrapped. |t is worthwhile even considering whether a time limit, perhaps 
of five years, might be agreed for the existence of the alternative methods 
in the standard. This would allow time for new equipment to be obtained 
before the single method is mandatory. This section should also contain 
instructions for the reduction of the measured values, the adjustment of 
the origin to the centre of symmetry and the calculation of the residual 
distortion values. This mathematical statement is essential if surveyors 
using calibration certificates are to check the data presented to them, 
or are to feel confident that both they and the compiler of the certifi- 
cate mean the same thing by the figures presented. 
The third section should list the information to be presented in the 
calibration certificate - and it might well include a preferred layout of 
calibration certificate. 
The information should include the following items: 
D. All serial numbers necessary to identify the camera and its 
components. 
2. The settings of any camera adjustments, e.g. lens aperture, 
filter orientation, etc. 
3. The method of calibration used, as given in the International 
Standard. 
4. The choice of. any variables permitted in the International 
Standard, e.g. the emulsion and the exposure and processing 
conditions. 
5. The origin of measurement and the sign convention used, pre- 
ferably illustrated by sketches. 
6. The adjustment of the fiducial centre, i.e. to centre of 
symmetry. 
7. The actual measured values of distance r, in the.focal plane 
and the corresponding angle © in the object space. 
B. The calibration principal distance chosen. 
  
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