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less specialised personnel to undertake the necessary photography. 
At the University of Cape Town a young post-graduate surveying student has 
received sponsorship to undertake underwater photogrammetric research. À 
condition of sponsorship was that he should successfully attend a scientific 
diver's course. The difficulties of underwater illumination are well known 
and for the purpose of this particular project photographic distances under- 
water have been confined to approximately 2 metres or less. 
ACCURACY TESTS 
The writer in a previous paper (Adams 1980) described the establishment of 
a calibration field and the use of projective transformations, homogenous 
co-ordinates and collinearity equations to test the accuracy of a pair of 
Mamiya C 330 twin-lens reflex cameras used in a stereophotogrammetric mode. 
Using the same calibration field and similar techniques the NIKONOS III, 
equipped with a W-Nikkor 35mm/f2.5 lens, was tested to establish potential 
in air accuracies. Measurement of X-Y co-ordinates of 80 Common targeted 
points were made on the original negative pairs of convergent photography 
in a STEKO 1818 stereocomparator (resolution 5 um) and on paper prints (8x 
enlargement) using a summagraphics ID-2.11/48 digitiser (resolution O. 1mm) 
attached to a Tektronix 4051 graphic system. A summary of the results are 
given in Table 1. The results of these tests show that the NIKONOS III used 
in an in air mode and with a W.Nikkor 35mm lens attached fulfills the 
specified requirements of precision photogrammetry, even when using paper 
print enlargements and digitised co-ordinates. 
In order to undertake underwater tests it was necessary to first construct 
and co-ordinate a portable free net control framework {Fig 3), ‚It Is 
normally tedious and difficult to co-ordinate targets in a small free net 
control framework using traditional survey methods and a method has there- 
fore been adopted of using a Zeiss Jena UMK 10/1318 metric camera to stereo- 
photograph the control framework placed within the permanent laboratory 
calibration field and then to co-ordinate the framework targeted points as 
an exercise in projective transformation. Tests have shown that the UMK 
camera is capable of achieving relative mean square errors of 1:10 000 of the 
distance from the camera. Using a framework of portable control points so 
co-ordinated, convergent underwater photography (Fig 3) was taken of the free 
net system at an overall ‘working distance of * 1 metre using the pair of 
cameras mounted on a bar and equipped with UW-Nikkor 28mm/f3.5 lenses. A 
typical set of results is listed in Table 1. 
Fryer and Elfick (1981) described an image splitter for simultaneous under- 
water stereophotography. A similar image splitter and including an attached 
control framework (Fig 4) was constructed and accuracy tests undertaken. A 
set of typical results is listed in Table II. Although the photographic 
coverage is reduced, the image splitter construction would be useful in the 
stereophotography and study of small marine life and so on, particularly 
where simultaneous photography was necessary. 
MEASUREMENT OF IMAGE PAIRS 
For the purpose of establishing the ultimate potential accuracy of the 
camera systems the original negatives of the image pairs were observed, as 
previously described, in a STEKO 1818 stereocomparator in mono-comparator 
mode and enlargement prints were observed on a Summagraphics digitiser 
tablet. The pointing mark on a normal digitiser cursor is coarse and 
consists of an etched Gross.” This type of measuring device is effective if 
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