4.2 MPS20 INTERIOR 
having created a job file, the user initiates interior orientation to 
compute the parameters required to transform from photo co-ordinates to 
the system used by the stereoviewer stages. An affine transformation is 
used to allow for the condition where a photograph may have a different 
scale in the X and Y direction due to factors such as film shrinkage. 
Up to 10 fiducial marks may be used for each photograph. 
The program reads the position of camera fiducials from the job file and 
drives the left and right photo stages to the approximate location of 
each fiducial in turn. The operator points to the correct location by 
use of the hand controls, and when all observations have been completed 
the interior orientation transformation parameters are computed and the 
results displayed. 
Operation, calibration and repeatibility of the NPS in interior 
orientation mode is checked by replacing the camera plate or fiducials 
with precision calibratrion grid plates. 
4.3 MPS30 EXTERIOR 
Having completed the interior orientation, the operator can proceed with 
the exterior orientation which computes the orientation and absolute 
position of the camera(s) at each photo site. 
The Exterior Orientation process can use a combination of absolute 
control and "pass points". The absolute control can take the form of 
control points, lengths, bearings and differences in any one of the two 
co-ordinates of two points. Control point names and co-ordinates must 
previously have been recorded in the appropriate job file. 
Pass points, that is points of detail which can be identified in both 
photos but for which control data is not available, can be located and 
digitised in order to strengthen the relative orientation between the 
photographs. Pass points assist in reducing the residual Y parallax 
where absolute control is not available in suitable looations in the 
model. 
The software drives the stages to certain set positions and waits for 
the operator to remove parallax and digitize a suitable point in the 
vicinity. 
When all observations are complete, the operator can select those to be 
used in the calculation, and the software computes the orientation 
parameters by a least squares technique. The results are then displayed 
for the user to accept, or reject. If rejected, points can be 
reobserved or the calculation be carried out with different points to 
overcome any problems in control. 
if the results are accepted, they are stored on disk file and sent to 
tne stereoviewer which then operates in orientation mode. 
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